What is the difference between a stratified random sample and a blocking sample.

Question

I don't see the difference between having a sample be "stratified" and blocking it?

Answer 1

A sample is stratified according to characteristics of the population...i.e. you can create sub-groups in a sample by age, and look at the data for different age groups. The experimenter doesn't control the characteristics that are stratified. A sample is blocked according to what will happen to them in the experiment. Some may get a placebo, or different dosages of a drug. The experimenter controls the characteristics that are blocked.