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Lecture 2 - Study Designs.ppt Lecture 2 - Study Designs.ppt
- 1.
- 2. Types of primarystudies • Descriptive studies – describe occurrence of (health) events • Analytic studies – describe association association between exposure and outcome/event
- 3. Basic Question inAnalytic Epidemiology • Are exposure and disease linked? Exposure Disease?
- 4. Basic Questions inAnalytic Epidemiology • Look to link exposure and health event –What is the exposure? ANC attendance –Who are the exposed? Pregnant women –What are the potential health effects? Improved delivery outcome –What approach will you take to study the relationship between exposure and effect? Design a study
- 5. Basic Research Study Designsand their Application to Nursing Research
- 6. Big Picture • Toprevent and control disease; inform clinical care • In a coordinated plan, look to –identify hypotheses on what is related to health event and may be causing it –formally test these hypotheses • Study designs direct how the investigation is conducted
- 7. What designs existto identify and investigate factors in health?
- 8.
- 9. Description of studydesigns by timeframe 1. Prospective Study - looks forward, looks to the future, examines future events, follows a condition, concern or disease into the future time Study begins here
- 10. Description of studydesigns by timeframe 2. Retrospective Study - “to look back”, looks back in time to study events that have already occurred time Study begins here
- 11. Study Design Sequence Casereports Case series Descriptive epidemiology Analytic epidemiology Clinical trials Animal study Lab study Cohort Case- control Cross- sectional Hypothesis formation Hypothesis testing
- 12. Descriptive Studies Case-control Studies CohortStudies Develop hypothesis Investigate it’s relationship to outcomes Define it’s meaning with exposures Clinical trials Test link experimentally Increasing Knowledge of Disease/Exposure
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- 14. Case Reports • Detailedpresentation of a single case or handful of cases • Generally report a new or unique finding • e.g. previous undescribed disease • e.g. unexpected link between diseases • e.g. unexpected new therapeutic effect • e.g. adverse events • e.g. new method of clinical management
- 15. Case Series • Experienceof a group of patients with a similar diagnosis • Assesses prevalent event • Cases may be identified from a single or multiple sources • Generally report on new/unique condition/technique • May be only realistic design for rare disorders/decisions
- 16. Case Series • Advantages •Useful for hypothesis generation • Informative for very rare disease with few established risk factors • Characterizes averages for disorder • Disadvantages • Cannot study cause and effect relationships • Cannot assess disease frequency
- 17. Case Report Case Series Descriptive EpidemiologyStudy One case of unusual findings Multiple cases of findings Population-based cases with denominator
- 18.
- 19. Analytic Study Designs •Experimental Studies – Randomized controlled clinical trials – Community trials • Observational Studies – Group data • Ecologic – Individual data • Cross-sectional • Cohort • Case-control – Case-crossover – Nested case –control • Before-after
- 20. Experimental Studies • treatmentand exposures occur in a “controlled” environment • planned research designs • clinical trials are the most well known experimental design. Clinical trials use randomly assigned data. • Community trials use nonrandom data
- 21. Observational Studies • non-experimental •observational because there is no individual intervention • treatment and exposures occur in a “non- controlled” environment • individuals can be observed prospectively, retrospectively, or currently
- 22. Cross-sectional studies • An“observational” design that surveys exposures and disease status at a single point in time (a cross-section of the population) time Study only exists at this point in time
- 23. Cross-sectional Design time Study onlyexists at this point in time Study population No Disease Disease factor present factor absent factor present factor absent
- 24. Cross-sectional Studies • Oftenused to study conditions that are relatively frequent with long duration of expression (nonfatal, chronic conditions) • It measures prevalence, not incidence of disease • Example: community surveys • Not suitable for studying rare or highly fatal diseases or a disease with short duration of expression
- 25. Cross-sectional studies • Disadvantages •Weakest observational design, (it measures prevalence, not incidence of disease). Prevalent cases are survivors • The temporal sequence of exposure and effect may be difficult or impossible to determine • Usually don’t know when disease occurred • Rare events a problem. Quickly emerging diseases a problem
- 26. Case-Control Studies • an“observational” design comparing exposures in disease cases vs. healthy controls from same population • exposure data collected retrospectively • most feasible design where disease outcomes are rare
- 27.
- 28. C as e- C on tr ol D es ig n Study population Cases (disease) Controls (no disease) factor present factorabsent factor present factor absent present past time Study begins here
- 29. Case-Control Study • Strengths –Less expensive and time consuming – Efficient for studying rare diseases • Limitations – Inappropriate when disease outcome for a specific exposure is not kn at start of study – Exposure measurements taken after disease occurrence – Disease status can influence selection of subjects
- 30. Hypothesis Testing: Case-CrossoverStudies • Study of “triggers” within an individual • ”Case" and "control" component, but information of both components will come from the same individual • ”Case component" = hazard period which is the time period right before the disease or event onset • ”Control component" = control period which is a specified time interval other than the hazard period
- 31. Cohort Studies • an“observational” design comparing individuals with a known risk factor or exposure with others without the risk factor or exposure • looking for a difference in the risk (incidence) of a disease over time • best observational design • data usually collected prospectively (some retrospective)
- 32. C o ho rt D es ig n time Study begins here Study population freeof disease Factor present Factor absent disease no disease disease no disease present future
- 33. Cohort Design: Timeframeof Studies • Prospective Study - looks forward, looks to the future, examines future events, follows a condition, concern or disease into the future time Study begins here
- 34. Prospective Cohort study Measureexposure and confounder variables Exposed Non-exposed Outcome Outcome Baseline time Study begins here
- 35. Cohort Design: Timeframeof Studies • Retrospective Study - “to look back”, looks back in time to study events that have already occurred time Study begins here
- 36. Retrospective Cohort study Measureexposure and confounder variables Exposed Non-exposed Outcome Outcome Baseline time Study begins here
- 37. Cohort Study • Strengths –Exposure status determined before disease detection – Subjects selected before disease detection – Can study several outcomes for each exposure • Limitations – Expensive and time-consuming – Inefficient for rare diseases or diseases with long latency – Loss to follow-up
- 38. Experimental Studies • investigatorcan “control” the exposure • akin to laboratory experiments except living populations are the subjects • generally involves random assignment to groups • clinical trials are the most well known experimental design • the ultimate step in testing causal hypotheses
- 39. Experimental Studies • Inan experiment, we are interested in the consequences of some treatment on some outcome. • The subjects in the study who actually receive the treatment of interest are called the treatment group. • The subjects in the study who receive no treatment or a different treatment are called the comparison group.
- 40. Experimental Study Designs •Randomized Controlled Trials (RCTs) – a design with subjects randomly assigned to “treatment” and “comparison” groups – provides most convincing evidence of relationship between exposure and effect – not possible to use RCTs to test effects of exposures that are expected to be harmful, for ethical reasons
- 41. E xp er im en ta l D es ig n time Study begins here(baseline point) Study population Intervention Control outcome no outcome outcome no outcome baseline future RANDOMIZATION
- 42. Experimental Study Designs •Randomized Controlled Trials (RCTs) – the “gold standard” of research designs – provides most convincing evidence of relationship between exposure and effect • trials of hormone replacement therapy in menopausal women found no protection for heart disease, contradicting findings of prior observational studies
- 43. Randomized Controlled Trials •Disadvantages –Very expensive –Not appropriate to answer certain types of questions • it may be unethical, for example, to assign persons to certain treatment or comparison groups
- 44. Review Questions (Developedby the Supercourse team) • Describe the link between exposure and disease • Describe study design sequence • Describe strengths and weaknesses of each design
Editor's Notes
- #1 Original Power Point file of this lecture
- #2 Descriptive studies may examine the frequency to which diseases occur. Analytic studies evaluates the relationship of disease/event to different exposures
- #3 Basic designs in epidemiology examine if exposures are associated with disease/health event. Does ANC attendance lead to delivery in a health facility?
- #4 In order to examine the link of exposure to health event, there needs to be standardized evaluation of exposure, as well as the event
- #5 • Society will be healthier • Society can save money on health care budgets • It will improve life expectancy • It will improve the economy Responses to this question vary. As outlined below, some believe that altruistically, society should pursue disease prevention to improve health and save money. These are noble goals, but I will demonstrate later that prevention does not always save money. The desire to prevent NCDs probably is a repercussion of our efforts to prevent infectious diseases. We have had great success in preventing communicable diseases. This has led to an initiative to prevent NCDs.
- #6 Prevention and control, can be defined as the reduction of the incidence of disease . May also imply improving convalescence or minimizing disability from disease
- #8 Health research studies may be descriptive in nature (describing the frequency or characteristics of events) or analytic (testing relationships between common traits and outcomes). Differing forms of descriptive studies exist. These designs are outlined in the next slide. Analytic studies include experimental designs (the randomized controlled trial) and observational designs (case-control studies, cohort studies, etc.). The case-crossover study design has received a lot of attention in the past few years.
- #9 With a prospective study one starts with cohorts of well individuals, and we wait until events occurs.
- #10 Looking backward is often difficult because of recall bias,, however, the case control studies are very inexpensive in comparison with prospective studies.
- #11 There are many different types of designs that are in the arsenal of the epidemiologists to investigate disease
- #12 To further illustrate, if one seeks to identify the etiologic factors (e.g. causal factors) behind an outcome (e.g. an MI), then each step in the epidemiologic framework provides new and important information. Descriptive studies are useful for identifying hypotheses to test in analytic studies. Case-control studies are then usually applied to evaluate if the hypothesized factor is related to the outcome of interest. Subsequently, cohort or longitudinal studies are applied to further define the importance of exposure to the causal agent for the development of the outcome.
- #13 • Society will be healthier • Society can save money on health care budgets • It will improve life expectancy • It will improve the economy Responses to this question vary. As outlined below, some believe that altruistically, society should pursue disease prevention to improve health and save money. These are noble goals, but I will demonstrate later that prevention does not always save money. The desire to prevent NCDs probably is a repercussion of our efforts to prevent infectious diseases. We have had great success in preventing communicable diseases. This has led to an initiative to prevent NCDs.
- #14 Case reports are in many ways “sentinel events” which can lead to testable hypotheses
- #15 Case series also provide suggestive evidence many times leading to more extensive testing.
- #16 Case series From Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Case_series
- #17 Descriptive study designs include case reports, case series, incidence studies, and ecologic studies. The case report is the most elementary study design in the literature. It generally describes an injury or injuries to one or two individuals that have been identified in a medical setting. There is also usually a unique feature to the noted chronic disease . The case series design is an extension of the case report. In a case series, a number of events are described. These events usually have been observed over a set period of time (such as one year) and are identified from one reporting source (e.g. a hospital). The descriptive epidemiology study is noted by the collection of events over a defined population base and by the use of denominator data to determine rates. The most frequent information generated from these designs are incidence rates for injuries. The ecologic study is a hypothesis generating study. Usually using group-level data, it examines if two factors are correlated with each other.
- #18 Responses to this question vary. As outlined below, some believe that altruistically, society should pursue disease prevention to improve health and save money. These are noble goals, but I will demonstrate later that prevention does not always save money. The desire to prevent NCDs probably is a repercussion of our efforts to prevent infectious diseases. We have had great success in preventing communicable diseases. This has led to an initiative to prevent NCDs.
- #19 An Introduction to Epidemiology (CDC) http://www.cdc.gov/excite/classroom/intro_epi.htm
- #20 Experimental studies are stronger in determining the etiology of disease than descriptive studies
- #22 Cross section al studies are some of the first studies completed because of ease and low cost
- #23 Cross-sectional studies examine a point in time
- #24 Cross-sectional studies involve point prevalence, not incidence. For very infrequent diseases they are of limited utility
- #25 Cross-sectional study From Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cross-sectional_study
- #26 Case-control studies in epidemiology are the most used type of study design
- #27 Case-Control studies represent one form of analytic study that provides information on the relationship between causal factors and injuries. In a case-control study, subjects who have been injured are identified and their past exposure to suspected causal factors is compared with that of controls (persons who have not been injured). Many case-control studies ascertain exposure from personal recall, using either a self administered questionnaire or an interview. The validity of such information will depend in part on the subject matter. People may be able to remember recent events quite well. On the other hand, long term recall is generally less reliable. Source: Chapter 8: Case-control and cross-sectional studies, Epidemiology for the Uninitiated
- #29 Case control studies provide low cost answers to health questions.
- #30 Case cross over studies are the newest form of epidemiologic design.
- #31 The cohort studies is the best for observational studies as the environmental event can be assessed before any disease outcome
- #32 A cohort studies follows a cohort of individuals who do not have disease, and then identified over time those individuals who have an outcome
- #33 Prospective cohort study From Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Prospective_cohort_study
- #34 Case-control studies are perhaps the most frequent form of analytic study design. These designs are very good for events that are rare in occurrence.. Still, there are some situations where cohort study designs would be appropriate in the field. The classic design in a cohort study is shown here. The study begins by assessing baseline levels of the exposure and other variables. Study subjects are then followed on a regular basis to identify the outcome. The frequency of outcomes are tested between persons who had exposure to the possible risk factor at baseline and persons with no exposure.
- #35 Prospective vs. retrospective studies http://www.statsdirect.com/help/basics/prospective.htm
- #36 An alternative form of the cohort study is something termed the retrospective cohort study. Other researchers may also call this a historical prospective study. This design is nearly identical to the prospective cohort study. The sequence of baseline exposure determination and longitudinal follow-up for outcomes is similar. The difference lies in the time in which the study begins. In this retrospective design, the researcher constructs the cohort study by looking back in time and placing data in the appropriate order and sequence. These studies are possible to do with large medical databases, such as the membership files of the Health Maintenance Organizations, or the medical files in the Scandinavian countries.
- #37 -- Exp. Measured before disease - so no temporal ambiguity -- Exposure measured before disease - so disease cannot influence the amount of error with which exposure status is measured -- Subject selection before disease, disease status does not influence of subjects
- #38 Experimental studies are the ultimate form of design in assessing causality as there is random assignment to groups.
- #39 Experimental Studies http://www.mcs.anl.gov/~itf/dbpp/text/node31.html
- #40 RCT should be conducted for hypotheses that have not been tested. Great care must be taken to evaluate possible negative outcomes as well as positive outcomes
- #41 Experimental and observational studies A common goal for a statistical research project is to investigate causality, and in particular to draw a conclusion on the effect of changes in the values of predictors or independent variables on dependent variables or response. There are two major types of causal statistical studies: experimental studies and observational studies. In both types of studies, the effect of differences of an independent variable (or variables) on the behavior of the dependent variable are observed. The difference between the two types lies in how the study is actually conducted. Each can be very effective. An experimental study involves taking measurements of the system under study, manipulating the system, and then taking additional measurements using the same procedure to determine if the manipulation has modified the values of the measurements. In contrast, an observational study does not involve experimental manipulation. Instead, data are gathered and correlations between predictors and response are investigated. From Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Statistics
- #42 It is not unexpected to find that observational studies find different results than for clinical trials. For example there have been 100s of observational studies demonstrating that hormone replacement was protective for women. However, when this was put to a clinical trail, the surprising result was that hormone replacement was not protective
- #43 Understanding controlled trials: Why are randomised controlled trials important? By Bonnie Sibbald and Martin Roland http://www.bmj.com/content/316/7126/201.full
- #44 We would appreciate your help with evaluating the content of this course. Please send completed Evaluation Form to super1@pitt.edu with the subject "chronic disease supercourse evaluation" If you have any comments or questions, please send a message to super1@pitt.edu