Determine threshold

Question

I have a series of probability of occurrence. Now I need to tell that above a certain percentage it's significantly different. Finally I need to determine a threshold.

By example : (%) = [ 2, 10 , 30, 50, 90] for each category.

In this example, naturally I say around 25%.

But how can I be sure about the value of the threshold please? Which method used please? and with which p value is significant?

Thanks for your replies.