Sir.—With regard to the article in the Journal by Dube et al, "Blood Pressure Studies in Black Children" (129:1177, 1975), I believe the authors failed to provide certain caveats concerning the proper interpretation of the results. Tables 6 and 7 contain regression equations that suggest (implicitly, perhaps) that one can estimate blood pressure from weight. These regression equations actually predict the average blood pressure for all children at that weight for a particular age; they can be used to predict individual results only when the correlation is quite high (ie, the scatter about the line is quite small). This is usually evidenced by a correlation of 0.8 or greater.
With correlations generally below 0.5, the constants in the equation are likely to be quite variable from study to study. This is particularly true when the correlations were not significantly different from zero (ie, one could not be sure if