I am prof Md Anisur Rahman Anjum head of the department (Ophthalmology) Dhaka Medical College

1. Study Design
Prof Md Anisur Rahman (Anjum)
Prof & Head of the department
Ophthalmology. Dhaka Medical College.
Dhaka
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2. What is research design?
• “A research design is the arrangement of condition
for collection and analysis of data in a manner that
aims to combine relevance to the research purpose
with economy in procedure”.
 It is a conceptual structure
 Blueprint for the collection, measurement and analysis of
data.
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3. study design
 What is Clinical study design?
 Clinical study design is the formulation of trials and
experiments in medical and epidemiological research
 Types of study designs:
 There are no hard and fast classification of study design
In broad scene we classify study design into two groups
1) Observational study and 2) Experimental study.
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4. Purposes of study design
 The purposes we will consider include:
1) Describing the prevalence of health problems;
2) Identifying causes of health problems (etiological research),
and
3) Evaluating therapy, including treatment and prevention
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5. Two types Study Design
Study Design
Experimental (The researcher
intervenes to change reality, and
then observes what happens)
Observational (The researcher
studies, but not alters what
occurs)
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6. Observational study:
Observational study: 4 things to be discuss:
1) When do we do an observational study?
2) Some key points of observational study
3) Types of observational study
4) Goal of observational study
 Another name of observational study is Non interventional
study or descriptive study.
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7. When do we do an observational study?
a) When we merely want to collect descriptive information: "Is
the incidence of diabetes rising?“
b) When we want to report on the causes of a problem without
disturbing the natural setting (I want to find out why students
do not attend lectures)
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8. When do we do an observational study?
c) When we can't do an experiment: "How fast does the earth
move around the sun?“
d) When it's not acceptable to do an experiment: "How much
does not wearing a condom increase the likelihood of HIV
infection
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9. Some key points of observational study:
1) Simply describe the problem e.g.
 pattern of disease occurrence,
 distribution of disease,
 general view of disease.
2) Provide general information about the relations of occurrence and
distribution of disease in population with basic characteristics
e.g. age, gender, religion, occupation, education, areas, time,
marital status, habit, social class etc.
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10. Some key points of observational study:
3) No research question and no attempt for answering the research
question.
4) Usually no hypothesis and don’t seek explanation or cause.
5) It is based on observation of naturally occurring events created by natural
experiments.
6) A sample of population is observed for various characteristics by
interview, questionnaire, measurement, records etc.
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11. Some key points of observational study:
7) How exposure occurs in natural setting. Nature determines
who is exposed to the exposure and who not. Researcher does
not determine the assignment of exposure; only passively observe the
events that unfold.
8) Subjects are not randomized to the exposed or unexposed groups,
rather the subjects are observed in order to determine both
their exposure and their outcome status and the exposure
status is thus not determined by the researcher.
9) It is regarded as precursor of analytic study.
10) Not structured formally like analytical and experimental study.
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12. Types of observational study
Observational study are of four main types;
1) Case-series,
2) Case-control,
3) Cross-sectional (including surveys), and
4) Cohort studies.
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13. Case-series study
Defination: When certain characteristics of a group (or series) of
patients (or cases) are described in a published report, the
result is called a case-series study.
 It is the simplest design in which the author describes some
interesting or intriguing observations that occurred for a small
number of patients.
 Case-series studies frequently lead to the generation of
hypothesis.
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14.  Cohort studies are used to study incidence, causes, and
prognosis. Because they measure events in chronological
order they can be used to distinguish between cause and effect.
 Case controlled studies compare groups retrospectively. They
seek to identify possible predictors of outcome and are useful
for studying rare diseases or outcomes. They are often used to
generate hypotheses that can then be studied via prospective
cohort or other studies.
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15.  Cross sectional studies are used to determine prevalence.
They are relatively quick and easy but do not permit
distinction between cause and effect.
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16. Objective Common design
Prevalence Cross sectional
Incidence Cohort
Cause (in order of
reliability)
Cohort, case-control, cross
sectional
Prognosis Cohort
Treatment effect Controlled trial
16Sunday, February 09, 2014 anjumk38dmc@gmail.com

17. Case-control, cross-sectional & cohort study
 These three types of studies (case-control, cross-sectional &
cohort study) are defined by the period of time the study covers and by
the direction or focus of the research question.
• Cohort and case-control studies generally involve an extended
period of time and it needs to take data several times
• For this reason, both cohort and case-control studies are
sometimes also called longitudinal studies.
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18. Case-control, cross-sectional &cohort study
• The major difference between them is the direction of the inquiry or
the focus of the of the research question.
• Cohort studies are forward-looking, from a risk factor to an
outcome, whereas case-control studies are backward-looking; from an
outcome to risk factors.
• The cross sectional study analyzes data collected on a group of
subjects at one time.
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19. Goal of observational study:
1) Alert community about the disease
2) Provide clue to etiology & hypothesis
3) Helps in planning of health care facilities
4) Focus on who, what, when & how questions.
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Did investigator assign exposure?
NO
EXPERIMENTAL STUDY
YES
OBSERVATIONAL STUDY
Random Allocation? Comparison Group?
YES NO NOYES
Randomized Control
Trial NON Randomized Control
Trial
ANALYTIC STUDY DESCRIPTIVE STUDY
Exposure to Outcome
Cohortstudy
Outcome
Exposure
Case-controlstudy
Exposure and outcome at the same time
Cross-sectionalstudy
According to time direction
Study design tree

21. Difference between descriptive study and analytic
study
Descriptive study Analytic study
Generate hypotheses Test hypotheses
Answer what, who, where, and
when
Answer why and how
Diffuse & superficial with research
question & answering but provide
useful insight into the problem
Narrow down to a specific research
question & its answering by more
rigorous study design & data
analysis
No attempt to analyze the link betn
exposure & outcome
Analyze the link betn exposure &
outcome
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22. Difference between descriptive study and analytic
study (Contd……)
Descriptive study Analytic study
Alert community about the
disease
Prove etiology & determinants
of disease
No comparison group Needs comparison group
Less ethical constrains Thorny ethical issue
More chance of bias. Less chance of bias.
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