3.research design

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


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


Features of good research design

• Flexible

• Appropriate

• Efficient

• Economical

• Minimises bias

• Maximises the reliability of collected data and analysed


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


Different research designs

Study designs

Observational

Descriptive

Case report Case series

Analytical

Cross-sectional

study

Case control study

Cohort

Experimental

RCT Non-RCT


Case report

• Studies describing the characteristics of a single patient


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


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


Case series

• Studies describing the characteristics of a group of patients with similar diagnosis

• Collection of 5 & more cases


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


Case series-Demerits

Cannot be used to test for the presence of valid statistical association due to absence of a comparison group


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


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


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


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


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


Case control study

Factor (s)

Present individuals with disease

TIME Direction of enquiry

Absent individuals w/o disease


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


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


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


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


Cohort study

• Proceeds from cause to effect

• Exposure has occurred when the study is

initiated, but the disease has not occurred


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


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


Randomization

• Simple randomization

• Block randomization

• Stratified randomization

• Unequal randomization


3.research design

Education