True rank

trueRank.fs

//Calculates the standard deviation 
let stddev(list:float list)=
    sqrt (List.fold (fun acc elem -> acc + (float elem - List.average list) ** 2.0 ) 0.0
                     list / float list.Length)

let trueRanks = [1.;2.;3.;4.;5.;5.;7.;8.;9.;10.]
let predictedRanks = [1.;2.;3.;4.;6.;7.;5.;8.;10.;9.]
let uBar  =  trueRanks  |> List.average

let upBar = predictedRanks |> List.average

let stdevTrue  = stddev trueRanks
let stdevPredicted = stddev predictedRanks

let n = 10.

let numerator = List.zip trueRanks predictedRanks 
                    |> List.map (fun item -> (float (fst item) - uBar) * (float (snd item) - upBar))
                    |> List.sum

let denominator = n * stdevTrue * stdevPredicted

let p = numerator /denominator