Problem in the formula of Standard Deviation

[Irshad Mujawar]

Hello Phil,

While using itemfit() function for missing data, the output showed some extra entities with SD_ character below the item fit statistics. Assuming that it stand for stand deviation I compared the entities with the formula, looks like something is not right.

ave[pick1, pick2] <- SD[pick1, pick2] <- 0

Here you are calculating sum(Xi), which is fine
       

 for (i in 1L:impute) ave[pick1, pick2] <- ave[pick1,
            pick2] + collect[[i]][pick1, pick2]

Here it is average  ( sum(Xi)/n) which is also fine.

        ave[pick1, pick2] <- ave[pick1, pick2]/impute

But here, you are only taking square over the difference (ave(Xi)  - Xi), where is the sum over i part ?

        for (i in 1L:impute) SD[pick1, pick2] <- (ave[pick1,
            pick2] - collect[[i]][pick1, pick2])^2

        SD[pick1, pick2] <- sqrt(SD[pick1, pick2]/impute)

Thanking you,

Irshad 

[Phil Chalmers]

You're right, that looks to be a typo. Fixed on the dev. Thanks for the report.

Phil

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