Question

When comparing a drug to placebo , should i use paired test or parallel test , he didn't mention number of groups or time interval

Answer 1

First of all, decide whether the same set of people or students are used for placebo and drugs or different sets are used.

For same set of people or students, paired t test is most suited because we have pair of observations of same set of people which will helps us in comparing the mean difference.

For different set of people or students, i.e. one set undergo placebo treatment and other set or group of people undergo the drug treatment, then parallel test is most suited because we have two parallel data set.

So, first check whether your data set is paired or unpaired, then select the paired t test for paired data and select parallel test for unpaired data.