I hope someone will be able to help me with this or point me in the right direction. I am writing up a report for Uni and have run an independent samples t-test on my data in SPSS. I get a p value of 0.049, less than 0.05 but only just.

Then I split my sample approximately in half (I wanted to separate people who spoke one language from people who spoke another). I have run the independent samples T test on each of the groups separately. Now they both come out as non significant.

I am not quite sure how to report this, can I say the results for the groups separately indicate I should question my 0.049 as indicative of a significant interaction and should use a more conservative critical value?

Why is it I get a significant result in one instance and then halving the sample size yeilds non significant results.

Is the significance I am finding for the whole group happening because the larger sample size is increasing type 1 errors?

Any tips, ideas, suggestions for something to read or look up, would be much appreciated!