What are the allocation methods used in independent samples experiments?

The allocation method simply refers to how the researchers decide who receives what treatment in an experiment. There are two ways to allocate participants:

a) Randomly

b) Selectively

Random allocation is when the researchers divide the participants and allocate them to certain groups using a random method. For instance, in an experiment to test the effects of a new drug on depression the researchers might use a random number generator to assign their 25 participants a number from 1 – 25. They could then put all the odds in one group and the evens in another.

When allocating participants selectively the researchers “select” who will go in each group based on a particular criteria. In the example above, for instance, there might be 8 females and 17 males so the researchers want to make sure that the number of female participants is equal in both groups so that gender is not a confounding variable. The would then make sure they chose four females to be in each group.