On-line statistics

Key for the selection of a test for comparisons

Are your data to be selected at random from the population you are studying?

Has every data point available got the same chance of being selected and are they independent from each other (ie not leaves from the same plant if you are comparing leaves between plants)?

These two points should be set in stone! If not the test results will be biased in one form or another and the conclusions that you make may be completely irrelevant. For example, if you were to sample a river bed with a net that had mesh size of 0.5mm but your species of interest had circumference of between 0.25 and 1.3mm, you would be including bias in your sampling by excluding those individuals smaller than 0.5mm.

Use the key by answering the questions in the most relevant way. It is advised that you double check through a good reference guide.

1. Have you got more than two samples?

No......go to 2

Yes.....go to 8

2. Have you got one or two samples?

One.....Single sample t-test

Two....go to 3

3. Are your data sets normally distributed (K-S test or Shapiro-Wilke)?

No.......go to 4

Yes......go to 5

4. Do your data sets have any factor in common (dependence), i.e. location or individuals?

No.Mann Whitney U test