Research design involves decisions about how to collect and analyze data to answer research questions or solve problems. There are two main types of research design: observational studies and experimental studies. Observational studies observe naturally occurring events without intervention, while experimental studies involve deliberate human intervention to change the course of events. Common research designs include descriptive studies, analytical studies, case-control studies, cohort studies, cross-sectional studies, and randomized controlled trials. Research design aims to ensure valid, unbiased conclusions through careful planning of study type, variables, data collection, and statistical analysis.

1. RAJESHWORINGAKHUSHI
RESEARC
H DESIGN

2. Research?
 Research is the systemic collection,
analysis and interpretation of data to
answer a certain question or solve a
problem.

3. Research design
Decisions regarding what, where, when,
how much, by what means concerning an
inquiry or a research study constitute a
research design
pattern, scheme, or plan to collect evidence
Depends on the objective of the proposed
study

4. Function – To permit valid conclusion which
should be justified and unbaised
Blue print of study

5. Defines
study type
sub-type
research question
 hypotheses
independent and dependent variables
experimental design
 data collection methods and a statistical
analysis plan

6. Research design have following
parts
Sampling design
Observational design
Statistical design
Operational design

7. Samplingdesigns
 Which deals with the methods of selecting items
to be observed for the study
Observational design
 Which relates to the condition under which the
observation are to be create

8. Statistical design
 Which concern the question of the of How
the information and data gathered are to be
analyzed ?
Operational design
 Which deals with techniques by which
the procedures satisfied in sampling .

10. Study design
Descriptive
Case study
Case Series
Surveys
Analytical
Prospective
Cross
sectional
Retrospectiv
e
Controlled
Randomized
Non
randomized
Non
controlled
Observational Experimental

11. Observational studies
Based on naturally occurring events
Observes and measures the
characteristics of interest to the study
Record based studies

12. Does not intervene or control the
factors related to exposure or outcome
Descriptive studies
Analytical studies

13. Descriptive study
 Study is designed primarily to describe
what is going on or what exists
 Involves describing the characteristics of a
particular situation, event and case in term
of time, place and person

14. Does not seek explanation or causes nor
tries to find which group is better relative to
other
Can also generate hypothesis regarding
aetiology of health condition
Can be designed to test a hypothesis

15. Helps to assess the type of diseases
prevalent in various groups and their load in
a community
Provide baseline data to launch a
programme and can measure achievements
made

16. Also good to study relationships ( systolic
and diastolic blood pressure)
Can be carried out on a large or small scale
Eg: Estimating prevalence of blindness in
cataract cases

17. Descriptivestudy
1
• Case study
2
• Case series
3
• Survey

18. Case study
 A case study is defined as the use of a single
person in a research study.
Generally describes features of a new
disease entity
In clinical medicine the characteristics of so
far unrecognized illness may be documented
as a case study

19. First step toward building up a clinical
picture of that illness
Can lead to a hypothesis

20. It allows to gain a lot of in-depth, detailed
information due to the close examination of
single case
Disadvantage - might not be true for other

21. Case series
Series of case study form case-series
Objective and brief report of a clinical
characteristics or outcome from a group of
clinical subjects
lead to the generation of hypotheses

22. Advantages:
1. Easy to write.
2. The observations can be extremely useful to
other investigators.

23. Disadvantages:
1. Susceptible to many biases.
2. They are not able for conclusive decisions
3. Unrepresentativeness of subjects
4. Lack of control group

24. Surveys
Community based investigation
Easy, simple and inexpensive
Large scale

25. Disadvantage:
1. It's difficult to truly test the impact of
certain variables when all people are doing
is filling out a survey
2. Some people might not be honest in their
survey responses.

26. Analytical study
Study designed to look at the relationships
or associations between two or more
variables
EXPLANATORY STUDY
To test hypothesis

27. Antecedent
An antecedent is a precursor such as an
exposure or a risk factor suspected to affect
the disease
Other terms - Cause , predisposing factor
and determinant

28. Outcome
Outcome could be a health state, recovery,
side effect, death or any other event of
interest
This is a consequence and must necessarily
occur after the antecedent
Other terms - Effect and result

29. Prospective study
Antecedents are assessed prior to the
outcome
Since outcome occurs after the antecedent,
follow up is essential
Umbrella term includes cohort, longitudinal
and follow up study

30. PROSPECTIVE STUDY
PRESENT
Diabetes
Mellitus
Time
Future Risk factors???
Retinopathy-
Retinopathy+

31. Prospective study
1
• Cohort
study
2
• Longitudinal
study

32. Cohort study
Word cohort has its origin in the Latin
cohors
Refers to a group of warriors and gives
notion of a group of persons proceeding
together in time( same statistical
characteristic )

33. A cohort is a group of people who have
something in common and who remain
part of a group over an extended time
Incidence study
“ What will happen?”.

34. Cohort study (Follow-up Studies)
Groups of people having similar attribute (cohort)
with & without a particular exposure, or an entire
community, or a random sample of a community
are selected for the study, enrolled & followed up
over time to determine their disease rates
Disease rates of exposed subjects are compared
with rates of an unexposed group or a group with
low exposure or with registry rates

35. Advantages:
1. Opportunity to measure risk factors before
disease occurs: evidence of causality
2. Can study multiple diseases outcomes
3. Can yield incidence rate as well as relative
risk estimates.
4. Good when exposure is rare
5. Minimizes selection and information bias

36. Disadvantages:
1. Expensive and inefficient for studying rare
outcomes
2. Often need long follow-up period and/or a
very large population
3. Losses to follow-up can affect validity of
findings
4. Ineffective for rare diseases
5. Expensive
6. Ethical issues

37. Longitudinal study
Another version of prospective study
When observation or measurements are
repeatedly made at several points of time
Repeated measures study

38. Longitudinal Study
Multiple points of data collection from the same
population
Initial point of
Data collection
(Present) Follow ups (Future)

39. Cross sectional
May be descriptive or analytic
Prevalence study/ Instantaneous study/
Simultaneous study
Examine the relationship between a disease and
an exposure among individuals in a defined
population at a point in time.
“What is happening?”

40. Antecedent and outcome are observed at the
same time
Also appropiate to generate hypothesis
regarding aetiology
Subsequently tested by a case control or a
prospective study

41. Cross sectional
One time data collection
Data collection
time

42. Advantages:
1. Useful to know the burden of a disease in a
group – prevalence rate can be obtained
2. Cheap and fast
3. Useful to evaluate diagnostic procedure
4. To study common risk factors and
outcomes

43. Disadvantages:
1. Population little willing to collaborate
2. Doesn’t tell the flow of events
3. Only shows association between factor and
disease studied
4. It is not useful to search causes of the
outcome

44. 5. It measure at a point of time therefore
mostly it is useful to study chronic diseases
6. Confounders may be unequally distributed
7. Group sizes may be unequal
8. Recall bias

45. Retrospective study
First assessed outcome and antecedents are
subsequently assessed
Outcome is already known and antecedent is
obtained either from records or enquiry

46. Cases and control are assembled
Information about their past exposure or risk
factors is collected

47. RETROSPECTIVE STUDY
Time
PAST
 Life style
 Diet
 Medication
 Family History
 Genetics
PRESENT
Disease
Determining differences in:

48. Case control design
Dominant format of retrospective study
Subjects with or without disease are
investigated for past exposure

49. Case- suffering from disease or have
interested health condition
Control – without particular health condition
“ What happened?”

50. Advantages:
1. Allows examination of several risk factors
2. Can study long-term effects of an exposure
in short period of time
3. Use fewer subjects,
4. Relatively quick and relatively less
expensive
5. Suitable for rare diseases

51. Disadvantages:
1. Selection of an appropriate control group
can be difficult
2. Recall bias: retrospective nature
3. Cannot tell about incidence or prevalence
4. Difficult to establish time relationship
between exposure and outcome

52. Choice of the wrong control group ~ selection
bias
Cases may over-report past exposures ~
information bias

53. Case control study
53
Comparative study done by involving two
population, i.e., case and control
This permits estimation of odds ratios (but
not of attributable risks)
Allowance is made for potential
confounding factors by measuring them and
making appropriate adjustments in the
analysis.

54. Basic steps
54
Selection of cases and controls
Matching
Measurement of exposure
Analysis and Interpretation

55. Case selection
Clinic/hospital records or staff
Death records
Special clinical exams or symptom/disease
questionnaire surveys
Special disease registries

56. Control selection
Other hospital/clinic patients (well or will)
General population registers (lists of
residents in a region)
People living in the same neighborhood as
cases
People with “other diseases” in disease
registries

57. Matching
57
Defined as the process by which we select
controls in such a way that they are similar
to cases with regards to certain pertinent
selected variables which are known to
influence the outcome of disease and
which, if not adequately matched for
comparability, could confound the results.

58. 58
A confounding factor is one which is
associated with exposure and disease, and
is distributed unequally in study and control
groups
It also independent risk factor to produce
the disease. e.g smoking works as
confounding in study of the role of alcohol
in duodenal cancer.

59. Measurement of exposure
59
Obtain data related to the exposure with risk
factors of the disease under study. The data
can be obtaining by:
 Interviews
 Using questionnaire
 Studying past records of cases form
hospital, other health institutions and
employment records.

60. Analysis
60
Odds Ratio: The ratio of probability of
getting disease with that of not getting
disease is Odds ratio.
Ratio of the odds of developing disease in
the exposed and the unexposed = a/b  c/d
= ad/bc
Odds ratio is an approximation of Risk
Ratio in rare diseases.

61. Nested case control design
Combine cohort and case control features
Since case control setup is nested within a
cohort
Eg: cohort of persons of age 40-44 years
who are followed up for 15 years for
development of cataract
Case- develop cataract
Matched control – did not develop cataract

62. • Relatively
inexpensive
• Much more
efficient
Advantages
• Suitable cohort
and specimen
may not be
available
Disadvantages

63. prospective
outcome
retrospective
antecedent Cross
sectional

64. Basis Cohort Cross
sectional
Case
control
Main
antecedent
Outcome
Recruitment
of subject
Definition of
case
Known
Elicited
Basis of
antecedent
Subject with
specified
antecedent
Elicited
Elicited
Neither
outcome nor
antecedent
Any subject
in defined
population
Elicited
Known
Basis of
outcome
Subject with
specified
outcome

65. Basis Cohort Cross
sectional
Case
control
Evaluation
and control
of
confounders
No of
subjects
Measure of
disease
frequency
Poor
large
Incidence
Fair
Large
Prevalence
Good
Small
Odds
obtained for
antecedent

66. Basis Cohort Cross
sectional
Case
control
To determine
whether
exposure
preceded
disease
If all factors are
not known
Time and money
Best
Best
Most
expensiv
e
Not
appropiate
Less
appropiate
In between
Not
appropiate
Not
Appropiate
Least
expensive

67. Experimental study
Require deliberate human intervention to
change the course of events
Often infeasible because of difficulties
enrolling participants, high costs, and big
ethical issues,
To prove hypothesis

68. Objectives
To provide scientific proof of etiological
factors which may permit the modification
or control of those disease
To provide a method of measuring the
effectiveness and efficiency of health
services for the prevention, control and
treatment of disease and improve the health
of the community

69. Usually compared two groups
One group in which intervention takes place
Another group that remained untouched

70. Clinical Trials Studies (experimental
studies)
 Involve humans are called clinical trials
studies because their purpose is to draw
conclusions about a particular procedure or
treatment
 used for evaluating the effectiveness of an
intervention (therapy research questions).

71. Animal studies
Laboratory studies

72. Advantages:
1. Give a strong causality evidence
2. Less bias
3. Historic controls can be used in preliminary
study

73. Disadvantages:
1.Expensive
2. Ethical issues
3. They need time
4.Participant compliance

75. Controlled trials are studies in which the
experimental drug or procedure is compared
with another drug or procedure as usually
previously accepted or placebo treatment.
Uncontrolled trials are studies in which the
experimental drug or procedure is described
being not compared with another treatment.

76. a) Randomized Controlled
Trials
Provides the strongest evidence for
concluding causation
It provides the best insurance that the result
was due to the intervention only

77. Provide that each individual has the same
chance of receiving each of the possible
interventions, so allocation of subjects in
experimental or control group is given by
chance.
Ensures that known and unknown
confounding factors are equal in both group,
(reduce bias)

78. b) Nonrandomized Controlled
Trials
Clinical trial or comparative studies with no
mention of randomization as well
Considered much weaker because they do
nothing to prevent bias in patient
assignment.

79. Field trials
 In contrast to clinical trials, involve people who are
disease free but presumed to be at risk; data
collection take place ‘in the field’, usually among
non-institutionalized people in the general
population
 Purpose is to prevent the occurrence of the
diseases that may occur with relatively low
frequency, field trials are often huge undertakings
involving major logistic and financial
considerations

80. Contd…
 Field trial method can be used to
evaluate interventions aimed at
reducing exposure without
necessarily measuring the
occurrence of the health effects
 E.g Blood lead levels in children
has shown the protection provided
by elimination of lead paint in home

81. Community trials
 In this form of experiment the
treatment groups are communities
rather than individuals
 Appropriate for diseases that have
their origins in social conditions,
which in turn can most easily be
influenced by intervention directed
at group behavior as well as at

82. True experimental research designs
 where researchers have complete control over the
extraneous variables & can predict confidently that
the observed effect on the dependable variable is
only due to the manipulation of the independent
variable
 Essentially consist of the following three
characteristics:
Manipulation
Control
Randomization

83. Quasi-experimental research design
 involves the manipulation of independent variable
to observe to effect on dependant variable, but it
lacks at least one of the two characteristics of the
true experimental design;randomization or a
control group

84. PRE –EXPERIMENTAL RESEARCH
DESIGN
 This research design is considered very
weak, because the researcher has very
little control over the experiment
 Most suitable design for the beginners in
the field of experimental research

85. Type of study Ability to prove
causation
Randomised controlled
trials
Cohort studies
Case control studies
Cross sectional
studies
Strong
Moderate
Moderate
weak

86. Quantitative vs. Qualitative
 Quantitative Research
is based on the
measurement of
quantity or amount.
 It is applicable to
phenomenon that can
be expressed in terms
of Quantity.
• Qualitative Research
is concerned with
Qualitative
phenomena related to
quality of kind,
human behaviour,
attitudes, motives,
etc.

87.  Measurement in various study designs
Prevalence
Incidence
Odds ratio
Relative risk
Attributable risk

88. Standard 2X2 contingency table
disease
Yes No
exposure
Yes a b
No c d
Total (a + c) (b + d)
88

89. Prevalence rate
Measured by cross sectional study
Prevalence rate = No of all cases under
study at a specified time in specified
population/ No of persons in the
population at risk at a specified time X
1000

90. Incidence rate
No of new cases of a disease under study
during a specified period of time/ total
susceptible population or population at risk
of developing the disease under study during
a specified period of time X 1000
Cohort study

91. Odds ratio
A measure of effect size
Measured in case control studies
Ratio of the odds among exposed to the
odds among unexposed
OR of 1indicates that the condition or event
under study is equally likely in both groups

92.  According to standard 2X2 contingency
table
 Odd of disease among exposed = a/b
 Odd of disease among unexposed = c/d
 OR = (a/b) / (c/d) = ad/ bc

93. Geater than 1 indicates that the condition or
events is more likely in the first group
Less than 1 indicates that the condition or
event is less likely in the first group
OR increases strength of association also
increases

94. Relativerisk / Riskratio
Risk of an event ( developing disease ) relative to
exposure
A ratio of the probability of the event occuring in the
exposed group versus a non exposed group
According to standard 2X2 contingency table
Risk of disease among exposed = a/a+b

95. Risk of disease among unexposed = c/c+d
RR = risk among exposed / risk among
unexposed
For null hypothesis, risk ration will be equal
to 1

96. RR more than one shows an association
Weak association RR >1 and < 2
Moderate to strong RR = 2 – 4
Very strong RR > 4

97. Attribute risk / risk difference
Simply a rate of disease in the exposed
people minus the rate in the unexposed
people
According to standard 2X2 contingency
table
Risk among exposed – risk among non
exposed

98. Risk of disease among exposed = a/ a+b
Risk of disease among unexposed = c/c+d
AR = risk among exposed - risk among
unexposed
For null hypothesis, AR = 0

99. References
 Basis methods of medical research
A. Indranarayan, 3rd edition
 Previous presentation
 Internet
 Research methodology for
health professionals
RC Goyal
 Park’s textbook of Preventive and social
medicine, 22nd edition

100. THANK
YOU
!!!