I have two groups of people, N=211 in group 1, N= 310 in group 2.
I would like to combine these groups because they share a certain characteristic that I am interested in. The groups are used in a multiple regression, so I only have the regression coefficients and CI's. They are:
group 1: -.05 (-.21 to .11) group 2: -.14 (-.27 to .00)
Is it possible to combine the groups? I did a similar calculation fot two other groups with the Cochrane combine groups formula. However, those groups had a mean, N and SE. Does anyone know if I can combine these 'regression' groups as well?
Edited in response to answer
Thank you for the response, In following your advice I came to the following outcome:
SE= (upper limit-lower limit)/3,93 (Cochrane handbook) y= width CI/2*1,96 S2= SE*SE
This resulted in:
SE y S2 group 1 0,08163 0,3136 0,006663457 group 2 0,06888 0,2646 0,004744454
Applying the inverse method resulted in: S2 combinede = 102,833/360,845= 0,285. Is that correct or am I missing something? And I only have the weighted shared variance now, right? How do I calculate the average weighted regression coeffiecient?
Thanks to mdewey for the correct solution:
w1 1 / v1 150,0722545 b1 -0,05 w2 1 / v2 210,7723914 b2 -0,14
Overall estimate of coefficient y and variance w
wiyi -37,01174753 y -0,102569757
som(wi) 360,844646 w 0,002771276