Hello,

I have determined 2 parameters (mean_alpha and mean_delta) using 6 different methods for each participant. Now I need to find out if I can get the same values for the 2 parameters using the 6 methods. I used ttest and thought that p value must be insignificant for the values to be the same between methods. I used the code (ttest mean_alpha if method_nr....) to test mean_alpha (analogously also for mean_delta). Unfortunately, the p-values do not show that there is no difference between the methods. Is my analysis wrong? How can I still compare the methods? Can anyone please tell me what else I could do. Also, I did the same survey with the same participants after one month to see if the results are time-consistent. What is the best way to analyze this? Unfortunately, I have never done this before.

ttest mean_alpha if method_nr==1 |method_nr==2, by (method_nr) // p=0.0192
ttest mean_alpha if method_nr==1 |method_nr==3, by (method_nr) // p=0.0111
ttest mean_alpha if method_nr==1 |method_nr==4, by (method_nr) // p=0.1467
ttest mean_alpha if method_nr==1 |method_nr==5, by (method_nr) // p=0.0082
ttest mean_alpha if method_nr==1 |method_nr==6, by (method_nr) // p=0.1253

ttest mean_alpha if method_nr==2 |method_nr==3, by (method_nr) // p=0.0000
ttest mean_alpha if method_nr==2 |method_nr==4, by (method_nr) // p=0.4004
ttest mean_alpha if method_nr==2 |method_nr==5, by (method_nr) // p=0.7710
ttest mean_alpha if method_nr==2 |method_nr==6, by (method_nr) // p=0.1512

ttest mean_alpha if method_nr==3 |method_nr==4, by (method_nr) // p=0.0001
ttest mean_alpha if method_nr==3 |method_nr==5, by (method_nr) // p=0.0000
ttest mean_alpha if method_nr==3 |method_nr==6, by (method_nr) // p=0.1034

ttest mean_alpha if method_nr==4 |method_nr==5, by (method_nr) // p=0.2585
ttest mean_alpha if method_nr==4 |method_nr==6, by (method_nr) // p=0.1415


Furthermore, I tried also the following code, since it is shorter and nicer:

pwmeans mean_alpha, over(method_nr) pveffects


but then I got different p-values. For example, when I compare method 1 with the other methods, with this code it is significantly different only for method 6 and with the first code (ttest mean_alpha if method_nr==....) it was significantly different for method 2, 3, 5.


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Thanks.