REsearch design

1. Rerearch Design
Prof.Dr. Baydaa Hameed Abdullah

2. Definition
• A study design is a specific plan or protocol for
conducting the study which allows the
investigator to translate the conceptual
hypothesis into operational one.
• Study design is the plan for collection of data
to answer the research question.

3. What does research design do?
Helps take decisions about how to complete
the entire research:
• Validly
• Objectively
• Accurately
• Economically

4. Functions of Research Design
1. The identification and/ or development of procedures
and logistical arrangements required to undertake a study
2. Ensuring that the procedures are adequate in quality to obtain
valid, objective and accurate answers to the research
questions.

5. Classifications of Study Designs
Three types of classifications
on the basis of:
1. The number of contacts with the study population
2. The reference period of the study
3. The nature of the investigation

6. Classifications of Study Design

9. Advantages of descriptive studies
1. They use already available data.
2. They are less expensive and less time-
consuming.
3. They describe the pattern of disease
occurrence.
4. They formulate research hypothesis.

10. 1-Case reports
• Researcher(physician) who see unusual
presentation of a common disease and he
describes the findings of this case, case
description may take any relevant description
of the finding.
• An unusual case may add to our Knowledge
for example MI in very young person without
ECG findings is unusual presentation of MI.

11. 2-Case series(clinical series)
• When a group of cases of the disease are reported, but in this study
we can not:
*Study the aetiology of the disease
* Testing the hypothesis
* Have a control group
• But in the study it can help in generating hypothesis
• Example: vaginal cancer is very rare in young females if 10 cases
were reported and studied it may help us to generate a hypothesis
when we interrogated with stilbestrol taking during pregnancy
among their mothers(this canbe done by further studies)
• Discovery of AIDS was a case series
• Many clincal studies are case series

12. Advantages of case reports or case series
1. Use available clinical data
2. Detailed individual data.
3. Add to our knowledge.
4. Suggest need for investigation (hypothesis
generation).

13. Disadvantages of case report or case series
1.May reflect experience of one person or
one clinician.
2. No explicit(clear) comparison group.

14. 3-Ecological Studies:
based on studying of a group of people not
individual as in previous studies.
 Correlation data represent average exposure
level rather than individual level so we do not
have each person information
 Ecological studies can generate a hypothesis
and need further confirmation , it provides just
initial clues to causation
 Example : as meat consumption in different
countries increases prevalence of ca colon
increases , Cigarette smoking increases ca
lung prevalence increases as well

15. Advantages of Correlational
Study
1. They describe the disease in the entire
population in relation to the factor of
interest.
2. They use the correlation coefficient (r) to
measure the association between the two
variables of interest.
3. They are easy to do, inexpensive and can
be conducted quickly.
4. They represent the first step in searching
for exposure-disease relationship
(generate hypothesis)
5. They use available data (administrative or
other aggregate data).

16. Disadvantages of correlational study
1. Correlation data represent average exposure
level rather than actual individual values. Data on
exposure and data on outcome are collected
independently.
2. No assurance that persons with exposure (risk
factor) of interest are the same ones with
outcome (disease) of interest.
3. Inability to link exposure with the disease in
particular individual.
4. What is missing: relationship between exposure
and outcome at the individual level (incomplete
design)

17. 4-Cross-Sectional studies
(prevalence studies or surveys)
Cross-sectional: where only ONE set of
observations is collected at a certain point in
time, disregarding the length of time of the
study as a whole
• It is a study of a group of people at a point in
time for the prevalence of a disease or an
attribute in a well defined population but data
is collected at individual levels. In this study
the measurements of exposure and effect
are made at the same time . In cross-
sectional studies, we are looking for both
exposure and outcome

18. Study Design based on
no. of contact with the population
Cross Sectional Studies:
• One-shot or Status studies: One time contact
• Most commonly used design in social sciences
• Obtain overall picture
• Very simple design:
Decide what you want to find out about, identify the study
population, select a sample and contact your respondents to
find out the required information

19.  Advantages of cross sectional study
1. Provide generalization from the sample to
the population.
2. They are short term studies and not
expensive.
3. Provide good information for the health
problems and good for health planners to
assess health care needs.
4. Used for generating hypothesis to be test in
further studies.5. Adapted to chronic
diseases

20. Disadvantages
1.It is difficult to separate cause and effect
1- because measurement of exposure and
disease are made at one point of time and it is
impossible to determined which came first.
2- Cases detected are prevalent cases
(survivors) leading to survival bias cases cured
or died are not detected.

21. 3.Possible measurement error; not suitable
for rare conditions;
4.Non response and this will affect the
representation of the sample.
5.Not adapted to incidence measurement
6.Not adapted to severe / acute diseases

22. Analytical studies
A case control study
• Begins with the selection of
cases(diseases) which should represent all
cases from a specified population.
• The most difficult task is to select
controls (people with no disease) the
controls should
• represent people who would have been
designated study cases if they had
developed the diseases.

23. Case control study
An important aspect of this study is the
determination of the start and duration of
exposure, the exposure status is usually
determined after the development of the
disease (retrospective) and usually by
direct questioning of the affected person.
Exposure may be determined by
biochemical measurement, established
recording system.

24. Case control
study
Disease
Controls
Exposure
?
?
Retrospective nature

25. Sources of selection of cases in case control
study
 Hospital-based case control study:
the cases will be identified from the
hospital or other health care facilities.
These are common, relatively easy and
inexpensive.
 Population-based case control study:
It involves locating and obtaining data
from all affected individuals or a random
sample from population.

26. Selection of controls in case control
study
 It is the most difficult aspect of Case
Control Study (CCS), it depends on:
1. Characteristics and sources of cases.
2. Need to obtain comparable and reliable
information from cases and controls.
3. Practical and economic considerations.

27.  The control should be comparable to the
source of the population of cases.
 Any exclusion or restrictions made in the
selection of cases should be applied equally
to the controls and vice versa.

28.  Advantages:
1. Suitable for rare diseases .
2. Results can obtained quickly.
3. Relatively inexpensive and short term study
4. Small sample size
5. Available data
6. No ethical problem

29.  Disadvantages of case control studies
1. Incidence or absolute risk cannot be determined
directly from a case control study. Temporal
relationship exposure-disease difficult to establish
2. Difficulty in selection the control.
3. Case- control study rely upon retrospective data
which lead to recall bias.
4. Because the data are collected after
5. Can not use to establish prevalence be whether
(retrospectively) it is
difficultto
correlation is causal or not.

30. 2-Cohort Study:
(follow up study, prospective , panel study, longitudinal,
incidence)
Follow up study or incidence study Begin with a
group of people (a cohort) free of disease, who
are classified into subgroups according to
exposure to potential cause of disease, and the
whole cohort is followed up to see how the
subsequent development of new cases of the
disease differ between the groups with and
without exposure, cohort study is a longitudinal
study cohort study provides the best information
about the causation of disease and the direct

31. Cohort study
 Identify group of
 Exposed subjects
 Un exposed subjects
 Measure incidence of disease
 Compare incidence between exposed and
unexposed group

32. Population
Diseased
Exposed
Non-diseased
Diseased
Not exposed
Non-diseased
Time
Direction of inquiry
Figure shows cohort study design
Cohort

33. Experimental Design
• The researcher introduces the intervention
that is assumed to be cause of change
and waits until it has produced or has been given
sufficient time to produce the change.
• The independent variable can be
observed , introduced, controlled or manipulated
by the researcher.

34. • An experimental study can be carried out in either a
‘controlled’ or a ‘natural’ environment.
• Study population in a ‘controlled’ situation:
such as a room.
Study Population in a ‘natural’ situation,
population is in its natural environment

35. Blind Studies
• In a blind study, the study population does not know whether it
is getting real or fake treatment or which treatment modality.
• The main objective of blind study is to
isolate the placebo effect: the psychological effect
• Usually applied to studies measuring the effectiveness of a drug
or treatment.

36. Double- Blind Studies
• Concept similar to that of a blind study
except that it also tries to
eliminate researcher bias
by concealing the identity of the experimental and placebo groups
from the researcher.
Neither the researcher nor the study participants know who is
receiving real and who is receiving fake treatment or which
treatment model they are receiving.

37. THANK YOU