How to interpret p-values in statistics for psychology?

Question

Please explain how to interpret p-values as I just cannot get my head 'around' them, for example, what is the difference between 0.01 and 0.5% significant?

Answer 1

Oh doll I wish I could help you out here but maths of any kind was a massive struggle for me and I have avoided it ever since

Answer 2

p values in statistics refer to the probability that the results of an analysis of the data occured by chance. For example, let's say you were comparing two different fertilizers on plant growth and obtained the following results:

Mean growth with A = 5 inches +/- 0.5 inches

Mean growth with B = 8 inches +/- 2 inches

Here are some possible results of a t-test analysis:

B>A, p<0.01

B>A, p<0.05

B>A, p<0.1

In the first, you can be 99% certain the the difference between B and A was caused by the fertilizer.

In the second, you can be 95% certain the difference was caused by the fertilizer.

In the third, you can be 90% certain the difference was caused by the fertilizer.

In psychology (and most social sciences) it is usual to accept p<0.05 or lower (p<0.01; p<0.001) as being statistically significant.

The smaller the p value the smaller the probability that the results of an experiment were caused by chance.