3.research design
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Research Design
D.A. Asir John Samuel, BSc (Psy), MPT (Neuro Paed), MAc, DYScEd,
C/BLS, FAGE
Meaning of research design
• The arrangement of conditions for collection and analysis of data in a manner that aims to combine relevance to the research purpose with economy in procedure
Dr. Asir John Samuel (PT), Lecturer, ACP 2
Need for research design
• Smooth sailing of various research operations
• Yielding maximal information
• Minimal expenditure of effort, time & money
• Plan for house
• Advance planning of methods to be adopted for collecting relevant data and techniques to be used in analysis
Dr. Asir John Samuel (PT), Lecturer, ACP 3
Need for research design
• Efficient and appropriate design must be prepared before starting research operation OR futile
• Organize ideas in a form
• Possible to look for flaws & inadequacies
• Need for providing comprehensive review
Dr. Asir John Samuel (PT), Lecturer, ACP 4
Features of good research design
• Flexible
• Appropriate
• Efficient
• Economical
• Minimises bias
• Maximises the reliability of collected data and analysed
Dr. Asir John Samuel (PT), Lecturer, ACP 5
Features of good research design
• A research design should consider,
- Means of obtaining information
- Objective of the problem to be studied
- Nature of the problem to be studied
- Availability of time and money
• Emphasis on discovery of ideas and insights
• Hypothesis if casual relationship b/w variables
Dr. Asir John Samuel (PT), Lecturer, ACP 6
Different research designs
Study designs
Observational
Descriptive
Case report Case series
Analytical
Cross-sectional
study
Case control study
Cohort
Experimental
RCT Non-RCT
Dr. Asir John Samuel (PT), Lecturer, ACP 7
Case report
• Studies describing the characteristics of a single patient
Dr. Asir John Samuel (PT), Lecturer, ACP 8
Case report-merits
• Record unusual medical occurrences and can give the first clues in identification of a new disease or adverse effects of an exposure
• Only means of surveillance for rare clinical events
• Serve to elucidate the mechanism of disease and treatment
Dr. Asir John Samuel (PT), Lecturer, ACP 9
Case report-Demerits
• Cannot be used to test for the presence of valid statistical association because it is based on the experience of one person
Dr. Asir John Samuel (PT), Lecturer, ACP 10
Case series
• Studies describing the characteristics of a group of patients with similar diagnosis
• Collection of 5 & more cases
Dr. Asir John Samuel (PT), Lecturer, ACP 11
Case series-merits
• Helps in formulating a useful hypothesis regarding risk factors of disease or identifying a new disease or outcome of new treatment
• Informative for very rare disease with few established risk factors
• May suggest the emergence of a new disease or epidemic
Dr. Asir John Samuel (PT), Lecturer, ACP 12
Case series-Demerits
Cannot be used to test for the presence of valid statistical association due to absence of a comparison group
Dr. Asir John Samuel (PT), Lecturer, ACP 13
Cross-sectional studies
• Single examination of a cross section of population at one point of time
• Helps to generate a hypothesis
• Used to investigate non fatal diseases
• Both exposure and outcome (disease) are determined simultaneously for each subject
• Provide information about the frequencey or characteristic of disease
Dr. Asir John Samuel (PT), Lecturer, ACP 14
Cross-sectional studies-Merits
• Provide information about the frequency of an attribute and potential risk factors
• Helps to generate a hypothesis
• Can give a good picture about the health care needs of the population at the point of time
• Can be used to investigate multiple exposure and multiple outcome
• Suitable for chronic cases
Dr. Asir John Samuel (PT), Lecturer, ACP 15
Cross-sectional studies-Demerits
• Difficult to establish the time of sequence of events
• They are not suitable to investigate rare diseases, rare exposure or disease of short duration
• Being based on prevalent rather than incident cases
• Limited value to investigate etiological relationship
Dr. Asir John Samuel (PT), Lecturer, ACP 16
Case control study
• Type of analytical study
• By observation and analysis
• Retrospective evaluation to determine who
was exposed and who was not exposed –
retrospective study
Dr. Asir John Samuel (PT), Lecturer, ACP 17
Case control study
• To examine the possible relation of an
exposure to certain disease
- Identify the individual having the disease –
case
- Individual don’t have the disease –
comparison purpose
Dr. Asir John Samuel (PT), Lecturer, ACP 18
Case control study
Factor (s)
Present individuals with disease
TIME Direction of enquiry
Absent individuals w/o disease
Dr. Asir John Samuel (PT), Lecturer, ACP 19
Case control study
4 basic steps in conducting a case control study,
1. Selection of cases and controls
2. Matching
3. Measurement of exposure
4. Analysis and interpretation
Dr. Asir John Samuel (PT), Lecturer, ACP 20
Case control study – Merits
• Quick, less expensive
• Well suited for disease with long latent period
• Optimal for evaluation of rare diseases
• Can study etiological factors for a single disease
• Requires small sample than a cohort study
• No attrition (drop outs) problem
• Ethical problems are minimal, no risk to subjects
Dr. Asir John Samuel (PT), Lecturer, ACP 21
Case control study- Demerits
• More prone to bias
• Selection of appropriate control group may be
difficult
• Inefficient for evaluation of rare exposure
• Cannot directly measure incidence, can only
estimate relative risk
Dr. Asir John Samuel (PT), Lecturer, ACP 22
Cohort study
• Forward looking study
• Prospective study
• Incidence study
• Longitudinal study
• There is regular follow up over a period of
time Dr. Asir John Samuel (PT), Lecturer, ACP 23
Cohort study
Factor (s)
Individuals exposed Present
TIME Direction of enquiry
individuals unexposed Absent
Dr. Asir John Samuel (PT), Lecturer, ACP 24
Cohort study
• Proceeds from cause to effect
• Exposure has occurred when the study is
initiated, but the disease has not occurred
Dr. Asir John Samuel (PT), Lecturer, ACP 25
Cohort
• A group of people who share a common
characteristic or experience within a defined
time period
• Cohort must be free from disease under study
• Both groups (study cohort & control cohort)
should be equally susceptible for the disease
under study
• Should be comparable in all possible variables Dr. Asir John Samuel (PT), Lecturer, ACP 26
Cohort study
• Elements of a cohort study,
1. Selection of study subjects
2. Obtaining data on exposure
3. Selection of comparison group
4. Follow-up
5. Analysis
Dr. Asir John Samuel (PT), Lecturer, ACP 27
Cohort study - Merits
• Incidence can be calculated
• Examines multiple effects of a single exposure
• Provides direct estimate of relative risk
• Minimizes bias
• Dose-response ratios can be calculated
• Elucidates temporal relationship b/w exposure
& disease Dr. Asir John Samuel (PT), Lecturer, ACP 28
Cohort study - Demerits
• Inefficient for rare diseases
• Expensive and time consuming
• Involves large sample size
• Alters people behaviour
• Changes in standard methods or diagnostic
criteria of disease over prolonged follow-up Dr. Asir John Samuel (PT), Lecturer, ACP 29
RCT
• Basic steps in conducting a RCT,
1. Drawing up a protocol
2. Selecting reference & exp. Group
3. Randomization
4. Manipulation or intervention
5. Follow-up
6. Assessment of outcome Dr. Asir John Samuel (PT), Lecturer, ACP 30
Select suitable
population
Select suitable sample
Exclusions
Randomize
Experimental group
Control group
Intervention & follow-up Dr. Asir John Samuel (PT), Lecturer, ACP 31
SACKETT LEVEL OF EVIDENCE
Dr. Asir John Samuel (PT), Lecturer, ACP 32
Randomization
• Simple randomization
• Block randomization
• Stratified randomization
• Unequal randomization
Dr. Asir John Samuel (PT), Lecturer, ACP 33