This document discusses research methodology and critical appraisal of studies. It describes different types of study designs including observational studies like cohort and case-control studies, as well as interventional studies like randomized controlled trials. A hierarchy of evidence is presented with systematic reviews and meta-analyses considered the strongest type of evidence. Critical Appraisal Skills Programme checklists are referenced to help appraise different study designs. Key aspects of cohort and case-control studies are defined.

1. Assistant professor Rahem Mahdy Rahem
Hematopathologist / Department of Pathology
College of Medicine / University of Kufa
Research methodology

2. Critical appraisal
(Methodological quality)
Is the process of carefully and systematically examining of the
research to judge its contents.
It represent essential skill for evidence base medicine.
So when you can appraise the research in scientific way, you can
do and write proper and scientific research

3. Types of study designs
Observational studies (studied but not alter the relationship
between exposure and outcome)
Descriptive:
o Cross sectional study
o Case series
o Case report
Analytic:
o Cohort study
o Case control study
o Cross sectional study
Interventional studies:
o Random control trails and community trials.
Meta-analysis and systemic review
Clinical predictive role
Diagnostic study

4. The hierarchy of evidences
o Systemic review and meta-analysis
o Random control trails.
o Prospective Cohort study
o Retrospective Cohort study
o Nested Case control study
o Case control study
o Cross sectional study
o Case series and case report.
More validity
More establish causality
More strong evidences

5. CASP (critical appraisal skills program) aims to help people
develop the necessary skills to make sense of scientific
evidence, with checklists covering most designs of studies.
Critical Appraisal Skills Programme

6. Questions to help you make sense of case control study
Questions to help you make sense of cohort study
Questions to help you make sense of a trial
Questions to help you make sense of a diagnostic test .
Questions to help you make sense of a review
Questions to help you evaluate a clinical prediction rule.
Others.

7. • Observational, analytic, epidemiological, study that the
investigators just observe but not assign the association
between the outcome and exposure.
• Most frequently used study design.
• Principle: Identify group of patients have OUTCOME and
backward-looking for the EXPOSURE, or risk factors in
comparing with the control group.
• Cases and controls which are as similar as possible in all
respects except for the presence or absence of disease.
D E

8. • Cohort mean group of peoples derived from the study
population share a common features and free from disease.
• Observational, analytic, epidemiological, longitudinal study
that the investigators just observe but not assign the exposure
which occur naturally.
• Use to evaluate risk and benefits of medications.
• Principle: Identify group of peoples share common feature
(EXPOSURE) and free from disease, follow them over time and
observe the occurrence of OUTCOME that may include disease,
condition, event, death, change in behaviour.
E D

9. Analytic study use to assess a new diagnostic test or procedure
in compare with gold standard one.
Mainly assess the sensitivity, specificity, positive and negative
predictive value of new test or procedure.

10. • Interventional, experimental, prospective study in human.
• The investigators not just observe but assign the association
between the outcome and exposure.
• Studied 2 groups randomly allocated to receive or not the
experimental intervention.
• Intervention can be drugs, prophylaxis, diagnostic,
therapeutic, agents, regimens, procedures.

11. • It observational, descriptive or analytic study that the
investigators observe the population of interest, exposure and
all variables at same time (Snapshot).
• Information cannot determine any relationship that may exist,
but use to develop other methods to investigate such relation
between exposure and outcome.
• Assess is there relationship between 2 diseases or relationship
between E and D at specific time but give no clue to time
relation.
D E
Same time

12. Good Luck