Can these data be grouped? Whithin a certain population, I have selected three samples (in three different periods of time) and determined for each the frequency of individuals that present a specific characteristic. I want to determine if all these results can be grouped together or if there are differences between samples. Can I do it by performing a chi-square test for observed vs. expected frequencies and pooling the data if there are no significant differences?
If I do the sampling (three times also) in other populations, should I repeat the same procedure for each in order to determine if data from the same population can be pooled?

Question 1
If your dataset is something like this
Sample 1           Yes=200             No=180
Sample 2           Yes=156             No=130
Sample 3           Yes=300             No=320
You can use chi-squared test.
Question 2:
I am not sure if I understood your second question. What do you mean with other populations?  Please, give a practical example
