This will be very brief.

The answer to the question,  “What test do I use?”  is, “It all depends.”

If you have one group you can do the following:

• check the reliability.
• check the validity.
• look at relationships between variables.
• predict something from other variables.
• look at change across time.
• look at scores on one variable measured under different conditions (within group difference)

If you have two groups you can do the following:

• compare the two groups on one variable (between group difference).
• look at change across time between the two groups
• compare two groups on one variable under different conditions (within group difference).

If you have more than two groups, it gets more complicated and I’ll talk about that another day.  Most Extension work doesn’t have more than two groups.

So you can see, it all depends.  More later.