This was given as a part of the course of Research & Evidence-Based Medicine given to fourth-year medical students (2018)

1. Research Methodology and
Evidence Based Healthcare (EBHC481)
RESEARCH DESIGNS
DR. Samer Rastam MD, PhD
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Lecture 4
Level 8
Year 4

2. Research Methodology and
Evidence Based Healthcare (EBHC481)
Objectives
• Explain the deference between research design and research
methodology
• Define research design
• Discuss types of research design
• Explain question types are used in research design’s types
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3. Research Methodology and
Evidence Based Healthcare (EBHC481)
Research Design
• It is the framework or the plan for a study that is used as a
guide in collecting, analyzing and interpret the data.
• It is a blueprint that is followed in completing a study.
• It is the map that is usually developed to guide the
research.
• The single most important decision the investigator has to
make.
• In clinical research, there are two broad categories of study
designs, mainly observational and experimental
(interventional )
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4. Research Methodology and
Evidence Based Healthcare (EBHC481)
Role of study design in
clinical research
If we do not follow a specific study design we are creating a clinical anecdote

5. Research Methodology and
Evidence Based Healthcare (EBHC481)
1- Observational Design
Definition and Purpose
• Observational studies are studies where the investigator assesses
the association between an exposure and an outcome by just
observing what is happening among a group of subjects.
• The allocation of subjects is beyond the control of the investigator,
which represent a major possible cause of bias.
• There are two general types of observational designs: descriptive
studies, and analytical studies.
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6. Research Methodology and
Evidence Based Healthcare (EBHC481)
Observational vs. experimental studies
ExperimentalObservational
More costly
More difficult
Time-consuming
Less costly
Easier
Usually quick
Possible ethical problemsLess ethical problems
Minimal confounder effectsAffected by confounders
Result: causationResult: association

7. Research Methodology and
Evidence Based Healthcare (EBHC481)
2- Descriptive Design
Definition and Purpose
• A study that is not aimed specifically to test a hypothesis. The
primary concern is with description rather than with the testing of
hypotheses or proving causality.
• The wealth of material obtained in most descriptive studies allows
the generation of hypotheses, which can then be tested by
analytical or experimental designs.
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8. Research Methodology and
Evidence Based Healthcare (EBHC481)
Types of Descriptive studies
• Case report:
• A report that documents unusual medical occurrences that can
represent the first clue in the identification of new disease or
adverse effect of exposures
• Based on one patient).
• Includes a summary of the disease, such as the presentation
signs, symptoms, diagnostic studies, treatment course and
outcome.
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9. Research Methodology and
Evidence Based Healthcare (EBHC481)
• Example: A 17-Year-Old Boy With Right Face Palsy, Left Leg Weakness, and
Lytic Skull-Bone Lesions.
• We describe a pediatric patient with chronic HTLV-I infection who developed
complications associated with HTLV-I (i.e., adult T-cell leukemia/lymphoma and
HTLV-I-associated myelopathy/tropical spastic paraparesis).
• To our knowledge, this presentation in a child has never been described.
• The patient underwent a bone marrow transplant and, at the time of this
writing, was in remission.
• This case report highlights the fact that HTLV-related complications, previously
expected to occur after decades of infection, also can occur in pediatric
patients, particularly those who acquired HTLV-I perinatally.
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10. Research Methodology and
Evidence Based Healthcare (EBHC481)
• Case series:
• It is a collection of different case reports, thus based on more than
one patient.
Example
• Gottlieb et al (1981) described young men with a rare form of
pneumonia (Pneumocystis Carinii) AIDS
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11. Research Methodology and
Evidence Based Healthcare (EBHC481)
• Community diagnosis or needs assessment
• This kind of study entails collection of data on existing health
problems, programs, achievements, or groups at highest risk.
• Its purpose is to identify existing needs and to provide baseline
data for the design of further studies or action.
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12. Research Methodology and
Evidence Based Healthcare (EBHC481)
Analytical studies
• Used to investigate associations between disease and exposure.
• In other words, to explain disease occurrence, identifying causes of
disease or risk factors associated with increased risk of disease after
taking into account the effect of potential confounders.
• They allow testing hypothesis about exposure–disease relationships.
• The classification of studies into descriptive vs. analytic studies may
involve some ambiguity; for example, cross-sectional studies can be
both descriptive (e.g. prevalence surveys) and analytic (when used to
look at exposure–disease association). This distinction is not very
important. It is important, however, to understand key features,
theoretical and practical advantages and limitations of each type, to
consider all potential sources of bias and confounding.
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13. Research Methodology and
Evidence Based Healthcare (EBHC481)
Cross-sectional analytical studies (a snapshot in time)
• Data collection at one point of time (one-shot).
• Many cross-sectional studies do not aim at testing a hypothesis about an
association, and are thus descriptive.
• Many of them are aimed to provide a prevalence rate at a particular point in time
(point prevalence) or over a period of time (period prevalence).
• Included in this type of descriptive study are surveys in which the distribution of a
disease, disability, pathological condition, etc., is assessed.
• An important type is the KAP survey (survey of knowledge, attitudes and
practice).
• Among the more common types of research designs reported in medical
literature.
• Repeated cross-sectional surveys can be useful for studying trends.
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14. Research Methodology and
Evidence Based Healthcare (EBHC481)
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15. Research Methodology and
Evidence Based Healthcare (EBHC481)
Cross-sectional studies
Risk factor present
(Obesity, lack of PA..)
Risk factor present
Risk factor not present
Risk factor not present
Study
population
Free of disease
(DM)
Has disease
(DM)
Time
Study

16. Research Methodology and
Evidence Based Healthcare (EBHC481)
• Advantages of cross-sectional studies:
• Start with a reference population, so it is allow to estimate
the prevalence rates.
• Short-term, easy, and economical.
• They are the starting point for other studies, especially for
chronic common diseases.
• Disadvantages of cross-sectional studies:
• Since exposure and disease are measured at the same point
in time, it is not possible to establish temporality.
• They are prone to bias from selective survival (fast healing
or death)

17. Research Methodology and
Evidence Based Healthcare (EBHC481)
Ecological studies
• The unit of observation is not individuals, but an aggregate, a
geographical administrative locality, a cluster of houses, a town, a
whole country, etc.
• The comparisons may be between populations in different places
at the same time, or in a time series, by comparing the same
population (in one place) at different times.
• Ecological studies may take any of the following forms:
Descriptive, Case-control, Cross-sectional, Cohort, or
Experimental.
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18. Research Methodology and
Evidence Based Healthcare (EBHC481)
• Advantages
• Easy, cheap, and quick to conduct
• Useful to explore relatively new hypothesis; useful when interested in the effect from ecological
variables; when adequate measurement of individual-level variables is not possible or individual-
level study is not possible; for example, to study the effect of geographical and temporal factors
on disease
incidence or the effect of a government policy change on health outcomes.
• Disadvantages
• Difficult to interpret associations in etiological terms;
• The inference is limited with respect to individuals, due to high probability of ecological fallacy
when characteristics of individuals are wrongly inferred from grouped data
• Potential for systematic differences between places in disease coding and classification and the
exposure measurement;
• Usually rely on data collected for other purposes, which means data on different exposures or
factors may not be available.
• Difficult to control for confounding
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19. Research Methodology and
Evidence Based Healthcare (EBHC481)
References
1. Health Research Methodology- A Guide for Training in Research
Methods, 2nd Ed WHO, 2001
2. Introduction to Clinical Research for Residents, Saudi
Commission for Health Specialties, 2014
3. Oxford Handbook of Clinical and Healthcare Research,
Sumantra Ray, Oxford, 2016
4. Principles and Practice of Clinical Research, John I. Gallin, 2002
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