# What does it mean to be a function of something?

There is a sentence in Sokal and Rohlf's classic text [R.R.Sokal F.J.Rohlf; Biometry, 3rd ed., 1994: p.132, chapter 7 Estimation and Hypothesis Testing]:

The variance of means is therefore partly a function of the sample size on which the means are based.

In this specific case, I understand that the greater the sample size the lesser the standard deviation of sample means. But in general what does it mean to be a function of something? Relationship or dependence?

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"$A$ is partly a function of $B$" means that if you change $B$, even if you don't change anything else, the chances are that $A$ will also change.
@Sim, if $A$ is constant, Sokal et al would not write $A$ is partly a function of $B$ --- and you know it --- so why confuse OP? –  Gerry Myerson Dec 9 '12 at 11:49