Randomised Controlled Trial
The gold standard is the double blind randomised controlled trial. It has two arms: a study group and a control group. As discussed, blinding is designed to reduce observational bias and randomisation to reduce selection bias.
The advantages of a randomised controlled trial are:
- Evaluation of single variable
- Prospective study
- Reduces bias
- Allows for meta-analysis by combining several randomised controlled trials
Steps in setting up Randomised Controlled Trial
The following steps are required in setting up a randomised controlled trial:
Null hypothesis: there is no difference as opposed to the alternate hypothesis (there is a difference)
- Inclusion / Exclusion Criteria
Describe the criteria for exclusion and inclusion in the study
- Outcome Measure
Select outcome measure and the type of data. Data could be nominal, ordinal or continuous. Depending or the type of data, a test statistic is selected. If continuous data are normally distributed, parametric statistics (t-test) can be used. Alternatively, we can use a non parametric statistical test.
Assessment of bias; there could be selection bias, confounding bias or observational bias. Selection bias is reduced by randomisation. If there is a known confounding factor, stratification can be used to reduce confounding bias. Observational bias is reduced by blinding.
Power analysis is performed to estimate the number of patients required in the study. It is necessary to have an estimate of:
- Difference desired to detect
- Spread of data
- Significance level (α)
- Test statistic (power)
A pilot study might be required to estimate these parameters.
- Ethical Approval
- Informed Consent
- Collection of Data & Results
Use parametric or non parametric tests as appropriate. Usually computers are used in the analysis.
- Publication and Presentation of Data