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Unit VII: Epidemiological Methods By: Ibne Amin Demonstrator (INS) Khyber Medical University
Objectives At the completion of this unit learners will be able to: • Define study design, • Discuss classification of study design. • Describe the Descriptive study designs. • Discuss the Analytical study designs
Study design A study design is a specific plan or protocol for conducting the study, which allows the investigator to translate the conceptual hypothesis (Abstract Level) into an operational one((Measurable & Testable Level). 3
4 Study design A set of defined steps required to carry out research on a problem under study. The design will define: • How study subject are selected?(target population ,sample method • Method of sample size estimation • Procedure of data collection (Primary surveys, interviews, clinical tests) or secondary (hospital records, national surveys). Tools used: Questionnaires, laboratory tests, anthropometric measurements.Data collection timeframe: Cross-sectional (one-time), longitudinal (over months/years). • Procedure of data analysis(Cleaning and organizing data in statistical software (SPSS, Stata, R) • Types of statistical test required(T-Test for two groups , ANOVA (for multiple groups). Chi-square test, Pearson correlation.
Cont…. • The proof for evidence-based medicine is all collected via research, which uses a variety of study designs. • Different study designs provide information of different quality. • Therefore, you need to understand the strengths and limitations of each type of study design, as applied to a particular research purpose.
6 Classification of Epidemiological Research/Study Designs Descriptive Research Analytical Research
7 Descriptive Research Population based Individual based Case reporting Case series Ecological / Correlational Cross-sectional surveys
8 Analytical Research Observational Experimental / Interventional Randomized Control Trials Cohort study Quassi Case–control study Cross-sectional study
9 Objectives at various levels DESCRIPTIVE STUDIES 1. Knowing the frequency of disease 2. Knowing the distribution 3. Developing the hypothesis OBSERV A TIONAL ANAL YTICAL 1. Testing the hypothesis 2. Establishing association EXPERIMENTAL OR INTERVENTIONAL STUDIES 1. Strength of association 2. Establishing the Study Types Objectives
Study Types STUDY TYPES Descriptive ( hypothesis formulation) Individual based Case studies Case series Population based Ecological Analytical/Experimental (hypothesis testing ) Observational Case- control cohort Cross- sectiona l Interventional RCT’s (III) Quasi- Experiment al The researcher studies, but does not alter, what occurs The researcher intervenes to change reality, then observe what happens
Descriptive Studies • A descriptive study design is used in epidemiology to describe the distribution of diseases, health conditions, or other variables without analyzing cause-and-effect relationships. These studies provide an overview of who, what, when, and where regarding a health- related event. Characteristics of Descriptive Studies: • Focus on describing health conditions or behaviors. • Do not test hypotheses but generate them. • Help in identifying patterns, trends, and risk factors. • Often the first step before analytical studies. 11
Descriptive Studies • Describe only; do NOT examine associations between Exposure (E) and health Outcome (O). • Generally the purpose is to describe the variability in a health outcome and/or formulate hypotheses. • A descriptive study involves describing the characteristics of a particular situation event or case. • Descriptive studies can be carried out on a small or larger scale. 11
Types of Descriptive Studies Individual Based Case Study A study of one diseased individual, providing a detailed description of an uncommon disease; provides timely or rare information. OR A single patient’s clinical history is described in detail, and then discussed in relation to the literature. Almost always a rare unusual, or atypical case.
Types of Descriptive Studies Individual based Case Series :A case series is a descriptive study design that presents multiple cases of patients with a similar disease, condition, or treatment outcome. Unlike case reports (which focus on a single patient), case series analyze a group of patients to identify patterns, risk factors, and treatment responses. This study design is observational and does not include a control group, making it useful for generating hypotheses for further research. A study of multiple occurrences of unusual cases that have similar characteristics. Investigators can calculate the frequency of symptoms or characteristics of people with the disease. Results may generate causal hypotheses. Neither a case study nor a case series includes a comparison group.
case series table.
Case Report Case Series One case of unusual finding Multiple cases of finding Descriptive Study Designs
Types of Descriptive Studies Individuals Based Cross sectional Surveys cross-sectional survey is a type of observational study where researchers collect data from a population at a single point in time. It helps to measure the prevalence of a disease, condition, or specific characteristic in a group of people. Unlike longitudinal studies, which follow participants over time, cross-sectional surveys provide a snapshot of the health status, behaviors, or risk factors in a population at a given moment. – Subjects or institutions are surveyed in order to describe the prevalence of health outcomes and /or characteristics of a population 15
Example:Cross-Sectional Surveys A public health researcher wants to understand the prevalence of obesity among university students. They conduct a cross- sectional survey by selecting a random sample of students, measuring their BMI (Body Mass Index), and collecting data on their eating habits and physical activity. The results help identify how common obesity is in that population at the time of the survey. Key Features of Cross-Sectional Surveys: • Data is collected at one point in time (not over months or years). • It measures prevalence (how common a condition is in a population). • It is useful for identifying risk factors and trends in public health. • It does not determine cause and effect, only associations.
16 Descriptive Studies Population Based • Ecological An ecological study is a type of observational study that examines data at the population or group level rather than at the individual level. This means that instead of collecting data from individual participants, researchers analyze data from entire populations, such as cities, regions, or countries. Ecological studies are often used in public health research to identify associations between environmental factors, lifestyle patterns, and health outcomes. – An ecological study focuses on groups of people (rather than individuals) as the units of analysis. – The variables include measurements taken at the group level e.g. infant mortality rates of different countries.
Types of Observational Analytical Studies 17
Analytical (Non- Intervention) Studies Cross- sectional studies Case- control studies Cohort studies
Time is Key Present* Fxpos‹ire Diceace and Exposure Past:
Cross-sectional study A cross sectional study measures the prevalence of health outcomes or determinants of health, or both, in a population at a point in time or over a short period.
CROSS-SECTIONL STUDY Information is collected from each subject at one point of time Used to provide a snapshot of a population at a point in time The main out-come measure is prevalence Limited to the measurement of risk factor and out-comes at one simultaneous point in time Examples: screening surveys knowledge attitude and practice (K.A.P.) surveys
Target Population Sample Gather Data on Exposure and Disease Exposed; Do not have Disease Not Exposed; Have Disease Not Exposed; Do not have Disease Begin with: 4 groups are possible Exposed; Have Disease I Determine presence or absence of exposure & presence or absence of disease
a b c d No disease Disease Exposed Not Exposed a b c d a b c d No disease Disease Disease No disease Exposed Exposed Not Exposed Not Exposed II
a b c d a b c d No disease Disease Disease No disease Exposed Exposed Not Exposed Not Exposed a vs. Prevalence of disease compared in exposed and non exposed c a+b c+d Prevalence of exposure compared in diseased and non diseased vs. b+d a b a+c OR III
Advantages of cross-sectional •Outcomes and exposures measured at the same time • Uncovers associations for further study • Useful for hypothesis generation • Quick & cheap (no follow up) • Best way to determine prevalence • Questionnaire/interview based •Useful for assessing practice, attitudes, knowledge, beliefs , utilisation of services etc
Advantages of Cross-Sectional study • Can be conducted to assess the health care needs of the population • Helpful in measuring access and utilization of health services • Provides information between disease and various variables • Provides information regarding distribution of a disease • Determines burden of the diseases in a population. So helpful for planning purposes
Limitations of Cross-Sectional study • No temporal or time sequence so gives no information whether which comes first e.i. Cause or Disease • Gives no idea about natural history of the disease or etiology • Gives no measure of new cases occurrence • Not useful for rare exposures or rare outcomes
Begin with: Defined population Identify : Exposed N o n - r a n d o m i z e d Not exposed Develo p diseas e Do not develo p diseas Develo p diseas e Do not develo p diseas 8
Cohort Study Design • Cohort studies are also called “Follow-up or Incidence Studies”. • Because the data on exposure and disease refer to different points in time, cohort studies are also longitudinal. • Cohort studies have also been called “Prospective Studies”.
Cohort studies • The observation of a cohort over time to measure outcome(s) • Synonymous terms (Last’s) ◦Follow-up ◦Longitudinal ◦Prospective
Cohort studies Birth cohort: all individuals in a defined geographical area born in the same period (usually a year) Inception cohort: all individuals assembled at a given point based on some factor e.g. Workplace
Cohort Studies Exposure cohort: a group of individuals that potentially share a common exposure e.g. Radiation Disease cohort: a group of individuals with a specific disease.
Steps in Cohort Study • Cohort studies are conducted in three fundamental steps: 1. Identify cohorts of exposed and unexposed individuals who are free of the disease/outcome of interest at the beginning of the study. 2. Observe each cohort over time for the development of the outcome(s) of interest. 3. Compare the risks of outcomes between the cohorts.
COHORT STUDY DESIGN
■ Prospective cohort study — Concurrent cohort study or longitudinal study ■ Retrospective cohort study — Non-concurrent cohort or historical cohort study = Investigator 10
Prospective Retrospective Ambidirectional Recruitment Exposure Outcome Exposure Outcome Exposure Outcome Exposure Outcome Time Cohort studies
Motto t Staid/ COnäucted in 2000 200 0 Defined population N o n - r a n d o m i z e d Expose d Diseas e diseas e expose d Diseas e diseas e 1
Oiííe entiating between P 0 pe tive ond Ret 0 pe tive ■ Prospective cohort study — Investigator > Starts the study (from the beginning) with the identification of the population and the exposure status (exposed/not exposed groups) > Follows them (over time) for the development of disease > Takes a relatively long time to complete the study (as long as the length of the study) 1
CORducted in 2000 Disease Defined population N o n - r a n d o m i z e d Exposed No disease Not exposed Disease No disease 1980 2000 1
Oiííe entiating between P 0 pe tive ond Ret 0 pe tive ■ Retrospective cohort study — Investigator > Uses existing data collected in the past to identify the population and the exposure status (exposed/not exposed groups) > Determines at present the (development) status of disease — Investigator spends a relatively short time to: > Assemble study population (and the exposed/not exposed groups) from past data > Determine disease status at the present time (no future follow-up)
ÛO òined o tive a á Retto pe e Motto S my ■ Investigator uses existing data collected in the past to: — Identify the population and the exposure status (exposed/not exposed groups) — Follow them into the future for the development of the disease ■ Investigator — Spends a relatively short time to assemble study population (and the exposed/not exposed groups) from past data — Will spend additional time following them into the future for the development of disease
COHORT STUDY DESIGN • Cohort study measure: i. Incidence rate ii. Relative Risk iii. Attributable Risk
DESIGN OF A COHORT STUDY Disease Develop Disease Does not Develop Total Incidence Rate of Disease First Select Exposed Not Exposed a C b d a + b c + d a/a+ b c/c + d Then Follow to see whether
INCIDENCE RATE • Incidence in exposed group = a/ a + b • Incidence in unexposed group = c/ c + d • Incidence in total (exposed + unexposed) • = a + c a + b + c + d
RELATIVE RISK • Cohort study determine whether there is an association between exposure to a factor and development of a disease. • Relative Risk = Incidence in exposed Incidence in unexposed = a/ a + b c/ c + d
ATTRIBUTABLE RISK • This is determined by the “Attributable Risk”, which is defined as “the amount or proportion of diseases incidence (or disease risk) that can be attributed to a specific exposure”. • Attributable Risk is calculated as follow: • Risk Difference = (Incidence in exposed group ) – (Incidence in non-exposed group [Background risk]
Advantages of cohort studies • Useful for rare exposures • Useful for more than one outcome • Incidence of the outcome (and incidence rates) •Temporal relationship between exposure and outcome is clear as exposure status defined at start of study •If prospective, minimises bias in measurement of exposure • Sometimes the only ethical or legal way to do study • Stratification, nested case-controls, and multivariate analyses (adjustment) can be applied
Disadvantages of cohort studies • Not good for study of rare outcomes •If retrospective they rely on the adequacy of records •Exposed may be followed more closely than unexposed • If prospective they can be very expensive and slow •As they are follow up studies, the validity of results is highly sensitive to losses to follow up (migration, withdrawal, lack of participation, death)
CASE-CONTROL STUDY DESIGN
Case-control studies •An analytical epidemiologic study design in which individuals who have the disease under study, also called cases, are compared to individuals free of disease (controls) regarding past exposures. •Exposure differences between cases and controls are helpful to find potential risk or protective factors. The purpose is to determine if there are one or more factors associated with the disease under study.
CASE-CONTROL STUDY • Toexamine the possible relation of an exposure to a certain disease, we identify; 1. A group of individuals with the disease (called cases) and for purpose of comparison, 2. A group of people without the disease or outcome variable (called controls ). 3. Thestudy compares the occurrence of the possible cause in cases and in controls.
DESIGN OF A CASE-CONTROL STUDY
■ A case-control study is usually conducted before a cohort or an experimental study to identify the possible etiology of the disease —It costs relatively less and can be conducted in a shorter time ■ For a given disease, a case-control study can investigate multiple exposures (when the real exposure is not known) ■ A case-control study is preferred when the disease is rare because investigators can intentionally search for the cases — A cohort study of rare disease would need to start with alarge number of exposed people to get
Advantages of case-control Studies • Can be carried out quickly and quite cheaply • Useful for rare diseases and outcomes • Can study multiple exposures for a single outcome •Case control studies can be ideal for the study of rare diseases or those with a long latency •Compares odds of exposure between cases and controls
Disadvantages of case-control studies • Selection of control population, overmatching •Information bias as exposures – similar status determined after outcome has occurred e.g. Recall • Selection bias especially regarding controls •Cannot establish sequence of events (temporal relationship) • Not good for rare exposures •Cannot usually be used to estimate incidence rates, relative risks or attributable risks
EXPERIMENTAL STUDY DESIGN
Randomised controlled trial (RCT) ”An epidemiological experiment in which subjects in a population are randomly allocated into groups, usually called study and control groups to receive and not receive an experimental preventive or therapetuic procedure, maneuver, or interventition”
Randomized Control Trials (R.C.T) Randomized: Allocation of participants to various groups in random fashion Control: A control group is used to compare the effects of a particular treatment Trials: An experiment conduction. 60
Intervention group Control group Outcome measure Changed group during study Loss to follow up Loss to follow up Reference population Taraget population Sample Random Allocation RCT
RANDOMIZED CONTROLLED TRIAL • The true experimental study design (RCT) has three characteristics: 1. RANDOMIZATION - the researcher takes care to randomly assign subjects to the control and experimental groups. • (Each subject is given an equal chance of being assigned to either group.)
RANDOMIZED CONTROLLED TRIAL 2. CONTROL - the researcher introduces one or more control group(s) to compare with the experimental group. 3. MANIPULATION - the researcher does something to one group of subjects in the study. • Note: The strength of experimental studies is that by randomization of confounding variables.
RANDOMIZED CONTROLLED TRIAL • In Randomized Controlled Trial (RCT), we begin with a defined population. • Subjects in the study population are randomly allocated to intervention and control groups, and the results are assessed by comparing outcomes. • The basic design of RCT is given below;
Allocation of study subjects - randomization •Random = governed by chance •Randomization = allocation of individuals to groups by chance •Each sampling unit has the same chance of selection
Ranåomizaíion ■ Randomization is the process by which allocation of subjects to treatment groups is done by chance, without the ability to predict who is in what group 1
Pulpo e Ranåom zation ■ Primary purpose — Prevent bias in allocating subjects to treatment groups (avoid predictability) ■ Secondary purpose — Achieve comparability between the groups (there is no guarantee)
Strut feå Ranåom za /on ■ Stratified randomization is random assignment within groups defined by participant characteristics, such as age or disease severity, intended to ensure good balance of these factors across intervention groups 2
O ag of st at eå Ranåomizaíion Stratify by gender Stratify by age 360 U Randomize ’” FI’ each sub— group 600 male s 1,000 patients 240 ol d 180+ 120+ 150+ 50 = 500 400 female s 300 youn g 100 ol d 180+ 120+ 150+ 50 = 500
6olå Standa å oí S udy be ąn ■ Randomized trials are gold standard of study designs because the potential for bias {selection into treatment groups) is avoided 2
BLINDING IN RCT • Blinding represents an important, distinct aspect of randomized controlled trials. • The term blinding (masking) refers to keeping trial participants, investigators (usually healthcare providers), or assessors (those collecting outcome data) unaware of an assigned intervention, so that they are not influenced by that knowledge. • Blinding prevents bias at several stages of a trial.
task 81 nå ną ■ Masking or blinding is used to increase the objectivity of the persons dealing with the randomized study (to prevent prejudice) ■ Subjects who can be masked/blinded — Study participants — Caregivers/treaters — Data collectors/assessors of outcome — Data analysts — Investigators ■ Level of masking/blinding — Non-blinded (open) — Single — Double — Triple 32
Placebo ■ A placebo (from the Latin for °I will please”) is a medical treatment (operation, therapy, chemical solution, pill, etc.), which is administered as if it were a therapy, but which has no therapeutic value other than the placebo effect ■ A nocebo (from the Latin for “I will harm”) is treatment like aplacebo but which has a harmful result
77 TYPES OF BLINDING • Single Blind – The subjects are not knowing the group to which they are belonging . • Double blind trials – Neither the subject nor care giver is aware about the groups • Triple blind trials – The subject, the care giver (nurse or doctor) and the person doing the analysis are not aware about the groups in.
Advantages of RCT • Exposure in under control. • Due to randomization both intervention and control groups have similar characteristics. • By blinding the study, the observer and selection bias can be eliminated. • If properly designed & conducted, it can reduce the confounding. • Can confirm or refute etiological hypothesis. • Can evaluate the efficacy / effectiveness / efficiency of health services. • Best method for studying causal relationship. 76
Disadvantages of RCT • Ethical problems Due to adverse effects Due to benefits of intervention in the treated group Provision of Placebo • Relatively expensive 77
QUASI EXPERIMENTAL STUDY • In a Quasi Experimental Study, at least one characteristic of a true experiment is missing, either randomization or the use of a separate control group. • A quasi experimental study, however, always includes manipulation of an independent variable that serves as the intervention.
QUASI EXPERIMENTAL STUDY • One of the most common quasi experimental designs uses two (or more) groups, one of which serves as a control group in which no intervention takes place. • Both groups are observed before as well as intervention, to testif the intervention has difference. after the made any • The subjects in the two groups (study and control groups) have not been randomly assigned.
QUASI EXPERIMENTAL STUDY • Another type of design that is often chosen because it is quite easy to set up uses only one group in which an intervention is carried out. • The situation is analyzed before and after the intervention to test if there is any difference in the observed problem. This is called a "Before- After" study .
STUDY TYPES & STRENGTH OF EVIDENCE • Analytic Study involves the systematic evaluation of suspected relationships, for example, between an exposure and a health outcome. • Analytic studies typically provide stronger evidence concerning particular relationships. • An experimental design is the only type of study design that can actually prove causation.
Stronger methodology Less Bias Controls for comparison Fewer studies
References • Principles of Epidemiology in Public Health Practice, Third Edition An Introduction to Applied Epidemiology and Biostatistics • http://www.cdc.gov/ • Jhonhopkin university epidemiology lectures
THANK YOU

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Lecturebbbbbbbbbbbbbb 7 Study Designs.pptx

  • 1.
    Unit VII: EpidemiologicalMethods By: Ibne Amin Demonstrator (INS) Khyber Medical University
  • 2.
    Objectives At the completionof this unit learners will be able to: • Define study design, • Discuss classification of study design. • Describe the Descriptive study designs. • Discuss the Analytical study designs
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    Study design A studydesign is a specific plan or protocol for conducting the study, which allows the investigator to translate the conceptual hypothesis (Abstract Level) into an operational one((Measurable & Testable Level). 3
  • 4.
    4 Study design A setof defined steps required to carry out research on a problem under study. The design will define: • How study subject are selected?(target population ,sample method • Method of sample size estimation • Procedure of data collection (Primary surveys, interviews, clinical tests) or secondary (hospital records, national surveys). Tools used: Questionnaires, laboratory tests, anthropometric measurements.Data collection timeframe: Cross-sectional (one-time), longitudinal (over months/years). • Procedure of data analysis(Cleaning and organizing data in statistical software (SPSS, Stata, R) • Types of statistical test required(T-Test for two groups , ANOVA (for multiple groups). Chi-square test, Pearson correlation.
  • 5.
    Cont…. • The prooffor evidence-based medicine is all collected via research, which uses a variety of study designs. • Different study designs provide information of different quality. • Therefore, you need to understand the strengths and limitations of each type of study design, as applied to a particular research purpose.
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    6 Classification of Epidemiological Research/StudyDesigns Descriptive Research Analytical Research
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    7 Descriptive Research Population based Individualbased Case reporting Case series Ecological / Correlational Cross-sectional surveys
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    8 Analytical Research Observational Experimental/ Interventional Randomized Control Trials Cohort study Quassi Case–control study Cross-sectional study
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    9 Objectives at variouslevels DESCRIPTIVE STUDIES 1. Knowing the frequency of disease 2. Knowing the distribution 3. Developing the hypothesis OBSERV A TIONAL ANAL YTICAL 1. Testing the hypothesis 2. Establishing association EXPERIMENTAL OR INTERVENTIONAL STUDIES 1. Strength of association 2. Establishing the Study Types Objectives
  • 10.
    Study Types STUDY TYPES Descriptive (hypothesis formulation) Individual based Case studies Case series Population based Ecological Analytical/Experimental (hypothesis testing ) Observational Case- control cohort Cross- sectiona l Interventional RCT’s (III) Quasi- Experiment al The researcher studies, but does not alter, what occurs The researcher intervenes to change reality, then observe what happens
  • 11.
    Descriptive Studies • Adescriptive study design is used in epidemiology to describe the distribution of diseases, health conditions, or other variables without analyzing cause-and-effect relationships. These studies provide an overview of who, what, when, and where regarding a health- related event. Characteristics of Descriptive Studies: • Focus on describing health conditions or behaviors. • Do not test hypotheses but generate them. • Help in identifying patterns, trends, and risk factors. • Often the first step before analytical studies. 11
  • 12.
    Descriptive Studies • Describeonly; do NOT examine associations between Exposure (E) and health Outcome (O). • Generally the purpose is to describe the variability in a health outcome and/or formulate hypotheses. • A descriptive study involves describing the characteristics of a particular situation event or case. • Descriptive studies can be carried out on a small or larger scale. 11
  • 13.
    Types of DescriptiveStudies Individual Based Case Study A study of one diseased individual, providing a detailed description of an uncommon disease; provides timely or rare information. OR A single patient’s clinical history is described in detail, and then discussed in relation to the literature. Almost always a rare unusual, or atypical case.
  • 14.
    Types of DescriptiveStudies Individual based Case Series :A case series is a descriptive study design that presents multiple cases of patients with a similar disease, condition, or treatment outcome. Unlike case reports (which focus on a single patient), case series analyze a group of patients to identify patterns, risk factors, and treatment responses. This study design is observational and does not include a control group, making it useful for generating hypotheses for further research. A study of multiple occurrences of unusual cases that have similar characteristics. Investigators can calculate the frequency of symptoms or characteristics of people with the disease. Results may generate causal hypotheses. Neither a case study nor a case series includes a comparison group.
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  • 16.
    Case Report Case Series Onecase of unusual finding Multiple cases of finding Descriptive Study Designs
  • 17.
    Types of DescriptiveStudies Individuals Based Cross sectional Surveys cross-sectional survey is a type of observational study where researchers collect data from a population at a single point in time. It helps to measure the prevalence of a disease, condition, or specific characteristic in a group of people. Unlike longitudinal studies, which follow participants over time, cross-sectional surveys provide a snapshot of the health status, behaviors, or risk factors in a population at a given moment. – Subjects or institutions are surveyed in order to describe the prevalence of health outcomes and /or characteristics of a population 15
  • 18.
    Example:Cross-Sectional Surveys A publichealth researcher wants to understand the prevalence of obesity among university students. They conduct a cross- sectional survey by selecting a random sample of students, measuring their BMI (Body Mass Index), and collecting data on their eating habits and physical activity. The results help identify how common obesity is in that population at the time of the survey. Key Features of Cross-Sectional Surveys: • Data is collected at one point in time (not over months or years). • It measures prevalence (how common a condition is in a population). • It is useful for identifying risk factors and trends in public health. • It does not determine cause and effect, only associations.
  • 19.
    16 Descriptive Studies Population Based •Ecological An ecological study is a type of observational study that examines data at the population or group level rather than at the individual level. This means that instead of collecting data from individual participants, researchers analyze data from entire populations, such as cities, regions, or countries. Ecological studies are often used in public health research to identify associations between environmental factors, lifestyle patterns, and health outcomes. – An ecological study focuses on groups of people (rather than individuals) as the units of analysis. – The variables include measurements taken at the group level e.g. infant mortality rates of different countries.
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    Types of ObservationalAnalytical Studies 17
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  • 24.
    Cross-sectional study A crosssectional study measures the prevalence of health outcomes or determinants of health, or both, in a population at a point in time or over a short period.
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    CROSS-SECTIONL STUDY Information iscollected from each subject at one point of time Used to provide a snapshot of a population at a point in time The main out-come measure is prevalence Limited to the measurement of risk factor and out-comes at one simultaneous point in time Examples: screening surveys knowledge attitude and practice (K.A.P.) surveys
  • 26.
    Target Population Sample Gather Dataon Exposure and Disease Exposed; Do not have Disease Not Exposed; Have Disease Not Exposed; Do not have Disease Begin with: 4 groups are possible Exposed; Have Disease I Determine presence or absence of exposure & presence or absence of disease
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    a b c d Nodisease Disease Exposed Not Exposed a b c d a b c d No disease Disease Disease No disease Exposed Exposed Not Exposed Not Exposed II
  • 28.
    a b c d ab c d No disease Disease Disease No disease Exposed Exposed Not Exposed Not Exposed a vs. Prevalence of disease compared in exposed and non exposed c a+b c+d Prevalence of exposure compared in diseased and non diseased vs. b+d a b a+c OR III
  • 30.
    Advantages of cross-sectional •Outcomesand exposures measured at the same time • Uncovers associations for further study • Useful for hypothesis generation • Quick & cheap (no follow up) • Best way to determine prevalence • Questionnaire/interview based •Useful for assessing practice, attitudes, knowledge, beliefs , utilisation of services etc
  • 31.
    Advantages of Cross-Sectionalstudy • Can be conducted to assess the health care needs of the population • Helpful in measuring access and utilization of health services • Provides information between disease and various variables • Provides information regarding distribution of a disease • Determines burden of the diseases in a population. So helpful for planning purposes
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    Limitations of Cross-Sectionalstudy • No temporal or time sequence so gives no information whether which comes first e.i. Cause or Disease • Gives no idea about natural history of the disease or etiology • Gives no measure of new cases occurrence • Not useful for rare exposures or rare outcomes
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    Begin with: Defined population Identify : Exposed N on - r a n d o m i z e d Not exposed Develo p diseas e Do not develo p diseas Develo p diseas e Do not develo p diseas 8
  • 34.
    Cohort Study Design •Cohort studies are also called “Follow-up or Incidence Studies”. • Because the data on exposure and disease refer to different points in time, cohort studies are also longitudinal. • Cohort studies have also been called “Prospective Studies”.
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    Cohort studies • Theobservation of a cohort over time to measure outcome(s) • Synonymous terms (Last’s) ◦Follow-up ◦Longitudinal ◦Prospective
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    Cohort studies Birth cohort:all individuals in a defined geographical area born in the same period (usually a year) Inception cohort: all individuals assembled at a given point based on some factor e.g. Workplace
  • 37.
    Cohort Studies Exposure cohort:a group of individuals that potentially share a common exposure e.g. Radiation Disease cohort: a group of individuals with a specific disease.
  • 38.
    Steps in CohortStudy • Cohort studies are conducted in three fundamental steps: 1. Identify cohorts of exposed and unexposed individuals who are free of the disease/outcome of interest at the beginning of the study. 2. Observe each cohort over time for the development of the outcome(s) of interest. 3. Compare the risks of outcomes between the cohorts.
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    ■ Prospective cohortstudy — Concurrent cohort study or longitudinal study ■ Retrospective cohort study — Non-concurrent cohort or historical cohort study = Investigator 10
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    Motto t Staid/COnäucted in 2000 200 0 Defined population N o n - r a n d o m i z e d Expose d Diseas e diseas e expose d Diseas e diseas e 1
  • 43.
    Oiííe entiating betweenP 0 pe tive ond Ret 0 pe tive ■ Prospective cohort study — Investigator > Starts the study (from the beginning) with the identification of the population and the exposure status (exposed/not exposed groups) > Follows them (over time) for the development of disease > Takes a relatively long time to complete the study (as long as the length of the study) 1
  • 44.
    CORducted in 2000 Disease Definedpopulation N o n - r a n d o m i z e d Exposed No disease Not exposed Disease No disease 1980 2000 1
  • 45.
    Oiííe entiating betweenP 0 pe tive ond Ret 0 pe tive ■ Retrospective cohort study — Investigator > Uses existing data collected in the past to identify the population and the exposure status (exposed/not exposed groups) > Determines at present the (development) status of disease — Investigator spends a relatively short time to: > Assemble study population (and the exposed/not exposed groups) from past data > Determine disease status at the present time (no future follow-up)
  • 46.
    ÛO òined otive a á Retto pe e Motto S my ■ Investigator uses existing data collected in the past to: — Identify the population and the exposure status (exposed/not exposed groups) — Follow them into the future for the development of the disease ■ Investigator — Spends a relatively short time to assemble study population (and the exposed/not exposed groups) from past data — Will spend additional time following them into the future for the development of disease
  • 47.
    COHORT STUDY DESIGN •Cohort study measure: i. Incidence rate ii. Relative Risk iii. Attributable Risk
  • 48.
    DESIGN OF ACOHORT STUDY Disease Develop Disease Does not Develop Total Incidence Rate of Disease First Select Exposed Not Exposed a C b d a + b c + d a/a+ b c/c + d Then Follow to see whether
  • 49.
    INCIDENCE RATE • Incidencein exposed group = a/ a + b • Incidence in unexposed group = c/ c + d • Incidence in total (exposed + unexposed) • = a + c a + b + c + d
  • 50.
    RELATIVE RISK • Cohortstudy determine whether there is an association between exposure to a factor and development of a disease. • Relative Risk = Incidence in exposed Incidence in unexposed = a/ a + b c/ c + d
  • 51.
    ATTRIBUTABLE RISK • Thisis determined by the “Attributable Risk”, which is defined as “the amount or proportion of diseases incidence (or disease risk) that can be attributed to a specific exposure”. • Attributable Risk is calculated as follow: • Risk Difference = (Incidence in exposed group ) – (Incidence in non-exposed group [Background risk]
  • 52.
    Advantages of cohortstudies • Useful for rare exposures • Useful for more than one outcome • Incidence of the outcome (and incidence rates) •Temporal relationship between exposure and outcome is clear as exposure status defined at start of study •If prospective, minimises bias in measurement of exposure • Sometimes the only ethical or legal way to do study • Stratification, nested case-controls, and multivariate analyses (adjustment) can be applied
  • 53.
    Disadvantages of cohortstudies • Not good for study of rare outcomes •If retrospective they rely on the adequacy of records •Exposed may be followed more closely than unexposed • If prospective they can be very expensive and slow •As they are follow up studies, the validity of results is highly sensitive to losses to follow up (migration, withdrawal, lack of participation, death)
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  • 55.
    Case-control studies •An analyticalepidemiologic study design in which individuals who have the disease under study, also called cases, are compared to individuals free of disease (controls) regarding past exposures. •Exposure differences between cases and controls are helpful to find potential risk or protective factors. The purpose is to determine if there are one or more factors associated with the disease under study.
  • 56.
    CASE-CONTROL STUDY • Toexaminethe possible relation of an exposure to a certain disease, we identify; 1. A group of individuals with the disease (called cases) and for purpose of comparison, 2. A group of people without the disease or outcome variable (called controls ). 3. Thestudy compares the occurrence of the possible cause in cases and in controls.
  • 57.
    DESIGN OF ACASE-CONTROL STUDY
  • 58.
    ■ A case-controlstudy is usually conducted before a cohort or an experimental study to identify the possible etiology of the disease —It costs relatively less and can be conducted in a shorter time ■ For a given disease, a case-control study can investigate multiple exposures (when the real exposure is not known) ■ A case-control study is preferred when the disease is rare because investigators can intentionally search for the cases — A cohort study of rare disease would need to start with alarge number of exposed people to get
  • 59.
    Advantages of case-controlStudies • Can be carried out quickly and quite cheaply • Useful for rare diseases and outcomes • Can study multiple exposures for a single outcome •Case control studies can be ideal for the study of rare diseases or those with a long latency •Compares odds of exposure between cases and controls
  • 60.
    Disadvantages of case-controlstudies • Selection of control population, overmatching •Information bias as exposures – similar status determined after outcome has occurred e.g. Recall • Selection bias especially regarding controls •Cannot establish sequence of events (temporal relationship) • Not good for rare exposures •Cannot usually be used to estimate incidence rates, relative risks or attributable risks
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  • 62.
    Randomised controlled trial(RCT) ”An epidemiological experiment in which subjects in a population are randomly allocated into groups, usually called study and control groups to receive and not receive an experimental preventive or therapetuic procedure, maneuver, or interventition”
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    Randomized Control Trials(R.C.T) Randomized: Allocation of participants to various groups in random fashion Control: A control group is used to compare the effects of a particular treatment Trials: An experiment conduction. 60
  • 64.
    Intervention group Controlgroup Outcome measure Changed group during study Loss to follow up Loss to follow up Reference population Taraget population Sample Random Allocation RCT
  • 65.
    RANDOMIZED CONTROLLED TRIAL •The true experimental study design (RCT) has three characteristics: 1. RANDOMIZATION - the researcher takes care to randomly assign subjects to the control and experimental groups. • (Each subject is given an equal chance of being assigned to either group.)
  • 66.
    RANDOMIZED CONTROLLED TRIAL 2.CONTROL - the researcher introduces one or more control group(s) to compare with the experimental group. 3. MANIPULATION - the researcher does something to one group of subjects in the study. • Note: The strength of experimental studies is that by randomization of confounding variables.
  • 67.
    RANDOMIZED CONTROLLED TRIAL • InRandomized Controlled Trial (RCT), we begin with a defined population. • Subjects in the study population are randomly allocated to intervention and control groups, and the results are assessed by comparing outcomes. • The basic design of RCT is given below;
  • 69.
    Allocation of studysubjects - randomization •Random = governed by chance •Randomization = allocation of individuals to groups by chance •Each sampling unit has the same chance of selection
  • 70.
    Ranåomizaíion ■ Randomization isthe process by which allocation of subjects to treatment groups is done by chance, without the ability to predict who is in what group 1
  • 71.
    Pulpo e Ranåomzation ■ Primary purpose — Prevent bias in allocating subjects to treatment groups (avoid predictability) ■ Secondary purpose — Achieve comparability between the groups (there is no guarantee)
  • 72.
    Strut feå Ranåomza /on ■ Stratified randomization is random assignment within groups defined by participant characteristics, such as age or disease severity, intended to ensure good balance of these factors across intervention groups 2
  • 73.
    O ag ofst at eå Ranåomizaíion Stratify by gender Stratify by age 360 U Randomize ’” FI’ each sub— group 600 male s 1,000 patients 240 ol d 180+ 120+ 150+ 50 = 500 400 female s 300 youn g 100 ol d 180+ 120+ 150+ 50 = 500
  • 74.
    6olå Standa åoí S udy be ąn ■ Randomized trials are gold standard of study designs because the potential for bias {selection into treatment groups) is avoided 2
  • 75.
    BLINDING IN RCT •Blinding represents an important, distinct aspect of randomized controlled trials. • The term blinding (masking) refers to keeping trial participants, investigators (usually healthcare providers), or assessors (those collecting outcome data) unaware of an assigned intervention, so that they are not influenced by that knowledge. • Blinding prevents bias at several stages of a trial.
  • 76.
    task 81 nå ną ■Masking or blinding is used to increase the objectivity of the persons dealing with the randomized study (to prevent prejudice) ■ Subjects who can be masked/blinded — Study participants — Caregivers/treaters — Data collectors/assessors of outcome — Data analysts — Investigators ■ Level of masking/blinding — Non-blinded (open) — Single — Double — Triple 32
  • 77.
    Placebo ■ A placebo(from the Latin for °I will please”) is a medical treatment (operation, therapy, chemical solution, pill, etc.), which is administered as if it were a therapy, but which has no therapeutic value other than the placebo effect ■ A nocebo (from the Latin for “I will harm”) is treatment like aplacebo but which has a harmful result
  • 78.
    77 TYPES OF BLINDING •Single Blind – The subjects are not knowing the group to which they are belonging . • Double blind trials – Neither the subject nor care giver is aware about the groups • Triple blind trials – The subject, the care giver (nurse or doctor) and the person doing the analysis are not aware about the groups in.
  • 79.
    Advantages of RCT •Exposure in under control. • Due to randomization both intervention and control groups have similar characteristics. • By blinding the study, the observer and selection bias can be eliminated. • If properly designed & conducted, it can reduce the confounding. • Can confirm or refute etiological hypothesis. • Can evaluate the efficacy / effectiveness / efficiency of health services. • Best method for studying causal relationship. 76
  • 80.
    Disadvantages of RCT •Ethical problems Due to adverse effects Due to benefits of intervention in the treated group Provision of Placebo • Relatively expensive 77
  • 81.
    QUASI EXPERIMENTAL STUDY •In a Quasi Experimental Study, at least one characteristic of a true experiment is missing, either randomization or the use of a separate control group. • A quasi experimental study, however, always includes manipulation of an independent variable that serves as the intervention.
  • 82.
    QUASI EXPERIMENTAL STUDY •One of the most common quasi experimental designs uses two (or more) groups, one of which serves as a control group in which no intervention takes place. • Both groups are observed before as well as intervention, to testif the intervention has difference. after the made any • The subjects in the two groups (study and control groups) have not been randomly assigned.
  • 84.
    QUASI EXPERIMENTAL STUDY •Another type of design that is often chosen because it is quite easy to set up uses only one group in which an intervention is carried out. • The situation is analyzed before and after the intervention to test if there is any difference in the observed problem. This is called a "Before- After" study .
  • 86.
    STUDY TYPES &STRENGTH OF EVIDENCE • Analytic Study involves the systematic evaluation of suspected relationships, for example, between an exposure and a health outcome. • Analytic studies typically provide stronger evidence concerning particular relationships. • An experimental design is the only type of study design that can actually prove causation.
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  • 88.
    References • Principles ofEpidemiology in Public Health Practice, Third Edition An Introduction to Applied Epidemiology and Biostatistics • http://www.cdc.gov/ • Jhonhopkin university epidemiology lectures
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Editor's Notes

  • #4  sample size estimation n=Z2×P×(1−P)​/d2