736. J. Marschak to Harrod , 13 January 1938 [a]
University of Oxford, Institute of Statistics, 74 High Street, Oxford #
13 January 1938
I wonder whether you would consent to altering your excellent letter in one or two points. 
p. 1 para 4. It is not quite true that "At present it (= analysis of changes in differential fertility) is impossible". The "Decennial Supplement" issued by the Registrar-General in connection with the 1921 Census contained such an analysis (s[ee]. compendium between 1911 and 1921 in Carr-Saunders' Social Structure of England and Wales, New Edition (1937), p. 219  ), and the figures for 1931 are about to be published (Decennial Supplement for 1931). It is true that this does not permit us to trace the changes in occupational fertility "year by year" because both the numerator (number of births) and denominator (number of married males in a given occupation) are known only for the Census years. But the proposed amendment of the registration forms will also yield reliable results only for the years adjacent to the Census years because, while supplying accurate numbers of births for each year it will not help to ascertain the numbers of occupied married males for each year. The strong shifts between occupations (in Oxford, 1/6 of all insured persons changed their industrial category during 1936, e.g. great numbers went from retail trade into the motor industry) will thus distort the figures of occupational fertility in the inter-censual years, especially if we want figures, not referring to broad social groups--as used in the Decennial Supplements--but to single occupations, in order to study, as suggested in the last sentence of para 4 of your letter, the effects of experimental endowment schemes on single occupations.
I suggest therefore that the last two sentences (from "At present ..." to the end) of para. 4 should be omitted. 
On the other hand, I agree that the change in registration forms will change the present state of statistics in a useful way, 1) because the "number of children between 0-1 years of age" which is the basis of present decennial calculations is a poor substitute for the number of birth registrations, 2) shifts between single occupations from year to year may not affect substantially the broad differential fertilities of social classes, 3) the occupation of mother has not hereto been included in the calculations of the Registrar-General, perhaps because the census gives the occupation of all members of the household but not, e.g., of an absent mother, I suppose.
My second alteration proposal regards page 2 para 1 of your letter.  I have strong reasons to believe that members interested in the whole question of the Statistics Bill will oppose your amendment as superfluous, on the grounds that a new law is not required for introduction of new forms by the Registrar General; they will, however, at the same time make it clear that in their opinion this introduction will not give rise to any criticism in Parliament. To meet this situation and avoid ridicule, I suggest that the words after "he would do so" should be omitted and replaced by "unless he is encouraged by Parliament". 
[not signed or initialled]
2. A. M. Carr-Saunders and D. Caradog Jones, A Survey of the Social Structure of England & Wales as Illustrated by Statistics, Oxford: Clarendon Press, 1937 2 . On p. 219, a table summarizes the birth-rates in certain social classes in England and Wales, in 1911 and 1921.
3. Marschak's suggestion was not followed literally, although some changes were introduced: for a comparison of the original and the published version see note 3 to press item 19 .
4. Harrod ( 1938:2 ), press item 19 , [jump to page] .
5. The original draft (filed in HP VI/99/1) was not altered at this point.
- a. AL, not signed or initialled, two pages, in JMP 1275, Box 147, folder H. This is a draft, with several corrections and deletions, which Marschak kept as a copy. It is marked "Copy" on top of the front leaf.
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