3.research design
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Research Design
D.A. Asir John Samuel, BSc (Psy), MPT (Neuro Paed), MAc, DYScEd,
C/BLS, FAGE
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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
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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
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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
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Features of good research design
• Flexible
• Appropriate
• Efficient
• Economical
• Minimises bias
• Maximises the reliability of collected data and analysed
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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
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Different research designs
Study designs
Observational
Descriptive
Case report Case series
Analytical
Cross-sectional
study
Case control study
Cohort
Experimental
RCT Non-RCT
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Case report
• Studies describing the characteristics of a single patient
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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
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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
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Case series
• Studies describing the characteristics of a group of patients with similar diagnosis
• Collection of 5 & more cases
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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
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Case series-Demerits
Cannot be used to test for the presence of valid statistical association due to absence of a comparison group
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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
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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
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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
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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
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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
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Case control study
Factor (s)
Present individuals with disease
TIME Direction of enquiry
Absent individuals w/o disease
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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
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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
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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
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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
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Cohort study
Factor (s)
Individuals exposed Present
TIME Direction of enquiry
individuals unexposed Absent
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Cohort study
• Proceeds from cause to effect
• Exposure has occurred when the study is
initiated, but the disease has not occurred
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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
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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
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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
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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
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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
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Select suitable
population
Select suitable sample
Exclusions
Randomize
Experimental group
Control group
Intervention & follow-up Dr. Asir John Samuel (PT), Lecturer, ACP 31
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SACKETT LEVEL OF EVIDENCE
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Randomization
• Simple randomization
• Block randomization
• Stratified randomization
• Unequal randomization
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