Hi everyone, I am presently working on developing a function that computes the z value for group sequential analysis in R software and I am kind of stuck with the result I am having. the function returns estimated effect measure (in my case risk ratio), standard error, weight, variance and z-value.

the estimated effect measure and standard error seems to be consistent with value generated by othe rsoftware (TSA-software).

my main concern is the variance which I estimated using formular for risk ratio variance and then obtain the inverse as instructed in this manual (Thorlund K, Engstrøm J, Wetterslev J, Brok J, Imberger G, Gluud C. User manual for trial sequential analysis (TSA). Copenhagen Trial Unit, Centre for Clinical Intervention Research, Copenhagen, Denmark. 2011. p. 1-115. Available from www.ctu.dk/tsa). but can't seem to find a solution to the problem.

suggestion from anybody that has worked on group sequential meta-analysis should advice on what to do.

Can also share my R-code with interested person(s) maybe that's where the problem lies.Thanks