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Darwin Correspondence Project

From Francis Galton   30 May 1873

42 Rutland Gate SW

May 30/73

My dear Darwin

I am truly obliged by the schedule.1 A few others are sent, many are promised and I have much hope of useful statistical result in in many ways.— All I have thus far got confirms the belief that the families will be on the average very small. As for what the usual education will have been, I cannot yet guess.

In reply to your quere about the 50.—2 There seems—or it may be that I am stupid—that a word is omitted, displaced or somehow wrong, because the sense is not clear & I don’t know how to interpret the meaning of the phrase “—would their mean height probably give an approximate mean between all 50 of each nation.” but the following will probably include what you want.

If nothing else could be assumed about the two nations than that the 10 tallest out of 50 taken at hap-hazard from A had a mean height of α, and those from B of β, 1, it would be impossible therefrom to deduce either—

(1) α and β, the respective mean heights of the 50A & the 50B

or (2) the ratio of α to β. but if you grouped the 10 tallest in either case according to their heights, that is, so many between 5ft. 10 & 5ft. 11 so many between 5ft. 11 & 6ft 0.—&c it would be possible by comparing the run of these numbers with those in an ordinary Table of the Laws of Error, to estimate approximately both (1) and (2)

10 is too small a number to be serviceable—I shd. fear—in this way;—100 ought to give excellent results; in any case the degree of regularity with which the numbers happened to run would be the measure of the probability of the accuracy of the results

If you have any case you want worked out & wd. send me the figures I will gladly do it.

Ever sincerely yrs | Francis Galton


Thanks CD for completed questionnaire;

answers his query about determining mean heights of men.

Letter details

Letter no.
Francis Galton
Charles Robert Darwin
Sent from
London, Rutland Gate, 42
Source of text
DAR 105: A74–6
Physical description
5pp inc †

Please cite as

Darwin Correspondence Project, “Letter no. 8928,” accessed on 1 December 2021,

Also published in The Correspondence of Charles Darwin, vol. 21