Using data from another function

I can't tell exactly how your EffectSize function works, but I assume it's generating the table as a side-effect and not returning an object.

Assign the table to an object inside the function and then have the function return that object:

EffectSize=function(data,conf.level,statistic){
...
table <- functionThatMakesTable
return(table)
}

Then in your second function use EffectSize and extract information from the resulting table object:

InVar=function(data,conf.level,statistic){
weight=1/EffectSize(data,conf.level,statistic)[,4]
...
return(weight)
}

A cleaner approach would be to calculate the weight inside EffectSize and either return both the table and weight as a list or just the weight:

EffectSize=function(data,conf.level,statistic){
...
table <- functionThatMakesTable

print(table) # see the table in the output

weight <- 1/table[,4]

return(list(table, weight)) # or return(weight) if you just want to see the table and not use it later
}

Regarding your original code, as @Avinash points out, you have to apply a function to index the object it returns - you can't index the function itself.

To give a short answer: You cannot subset functions.

suppose you have ...

dummy <- function(){
  # doing some stuff
  results <- data.frame(1:3, letters[1:3])
  return(results)
}

what you cannot do is the following ...

dummy[1,]

.. but that one will work ...

dummy()[1,]

dummy[1,] tries to subset the object dummy. BEcause dummy is a function and not matrix or an data.frame it does not support this method.

On the other hand dummy()[1,] works because it tries subsetting the result produced by dummy() instead of the function itself.

Therefore, I suppose that instead of this line ...

weight=1/EffectSize[,4]

that one should work for you:

weight=1/EffectSize()[,4]