[R] Fisher transformation for pooling estimates - p values > 1

[lifty.gere at gmx.de]

Dear all,

I am using Fisher r to z transformation for pooling partial correlation estimates over multiple imputed data (number of imputations = 200). The number of observations in my data is 190. Unfortunately, when i calculate p values for the pooled estimates, some of them are p > 1 (ranging from 0 to 2). 

Here is the syntax I use. Can anybody help me find the error?

nobs <- dim(my_data)[1]

z <- log((1 + pcor)/(1 - pcor))/2
var_z <- rep(1/sqrt(nobs - 3), 200)

combine_z <- MIcombine(results=as.list(z), variances=var_z, call=sys.call())

pcor_pooled <- (exp(2*as.numeric(combine_z[1])) - 1)/
	          (exp(2*as.numeric(combine_z[1])) + 1)

# Calculate the upper and lower bounds
z_lower <- as.numeric(combine_z[1]) - qnorm(.975)*as.numeric(combine_z[2])
z_upper <- as.numeric(combine_z[1]) + qnorm(.975)*as.numeric(combine_z[2])
pcor_lower <- (exp(2*z_lower) - 1)/(exp(2*z_lower) + 1)
pcor_upper <- (exp(2*z_upper) - 1)/(exp(2*z_upper) + 1)

# Calculate the P-Value
pcor_p <- - as.numeric(combine_z[1])/as.numeric(combine_z[2])
pcor_pvalue <- 2*pnorm(-pcor_p)

Thank you!
Tina
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