The answer, of course, would be to obtain partial correlations (e.g., rBMI-IVF 'dot' age).

(We also speculated about whether the age-IVF relationship might be complicated by the role of BMI, for which similar considerations as above would apply.) A bivariate (or zero-order) correlation between BMI and IVF could be ambiguous because BMI might be carrying some influence of age. In an example I've used for many years (available in the links section), we can examine whether the relationship between Body Mass Index (BMI) and success at In Vitro Fertilization (IVF) might be complicated by BMI being positively correlated with age. In the sampling groups which are being tested (p. Himself or herself that no unrecognized confounding factor lies hidden Is probably the statistician's most difficult task of all to assure Lines, 1990) that puts the technique of partial correlation in some perspective: Here's a quote from the book Think of a Number (by Malcolm E. The idea is that one or both of the primary variables may also be correlated with a third (or fourth, etc.) variable, which could obscure our understanding of the original two-variable relationship. Partial correlations 'hold constant' or 'control for' one or more 'lurking' variables extraneous to your two primary variables. NOTE: I have edited and reorganized some of my writings on correlation to present the information more coherently ().

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