How can I compare the two means obtained for each stage between the two groups, to see if the difference is statistically significant?

In a few articles that I read they used pair-wise comparison, but I couldn't understand. Is there any special test to use? Should I compare the slopes of the probit lines only. I use SPSS and Minitab programs.

Any help provided at this point would be much appreciated.

Thanks in advance.

Kostas