Neither the test group nor the researchers know whether the test group is receiving a placebo or the actual treatment until all the data are collected.

The test group knows whether they are receiving a placebo or the actual treatment, and so do the researchers.

The test group knows whether they are receiving a placebo or the actual treatment, but the researchers do not know until all the data are collected.

The test group does not know whether they are receiving a placebo or the actual treatment, but the researchers do.