Purpose of double blinding in clinical trials

051. The purpose of double blinding in clinical trials is to:

1. Achieve comparability between study and control groups

2. Avoid observer bias

3. Avoid subject bias

4. Avoid observer and subject bias

Answer

4. Avoid observer and subject bias

Reference

Park 18^th Edition Page 77

Quality

Reader

Status

Repeat

QTDF

Park

Discussion

Bias may arise from errors of assessment of the outcome due to human element. These may be from three soruces – the participant, the observer and the interpretor. Randomisation cannot guard against these sorts of bias, nor the size of the sample. In order to reduce these problems, a technique known as “blinding” is adopted, which will ensure that the outcome is assessed objectively

Explanation

Blinding can be done is three ways

1. Single Blinding -
2. Double Blinding
3. Triple Blinding

Comments

Trials can be Open trial or Blind Trial

Open trial: In an open trial, the researcher knows the full details of the treatment and so does the patient. These trials are open to challenge for bias, and they do nothing to reduce the placebo effect. However, sometimes they are unavoidable, particularly in relation to surgical techniques, where it may not be possible or ethical to hide from the patient which treatment he or she received.

Open Trial	Participant aware	Possibility of Subject Bias
Single Blind Trial	Participant not aware whether he belongs to the study group or control group	Eliminates Subject Bias, but possibility of Observer Bias and Evaluation Bias
Double Blind Trial	Participant (patient) is not aware whether he belongs to the study group or control group And Observer (doctor) also is not aware whether he belongs to the study group or control group And	Eliminates Subject Bias and also observer Bias, but possibility of Evaluation Bias
Triple Blind Trial	Participant (patient) is not aware whether he belongs to the study group or control group And Observer (doctor) also is not aware whether he belongs to the study group or control group And Interpretor (epidemiologist) too is not aware whether he belongs to the study group or control group	Eliminates Subject Bias, observer Bias and also Evaluation Bias

Tips

Other types of Bias include

1. Recall Bias
2. Sampling Bias
3. Selection Bias