52 



A. Comfort 



stallions in the cohort sample; the two cross-sections differ 

 significantly from one another, from the mares, and from the 

 cohort. 



Table VI 



Expectation of further life (years) for thoroughbred 



MARES AND STALLIONS AT DIFFERENT AGES. (MeANS AND 

 STANDARD ERRORS.) 



We can take our choice among these findings. The cohort 

 sample is closest in date and method of treatment to the 

 samples of mares, but it is small, and depends on only 38 

 conventionally "natural" deaths, none of them under 8 years 

 of age, while of the two cross-sections, that for 1910-13 is 

 probably the better, on grounds of size and absence of intervals 

 in the middle of the table where q^ = 0. 



Over most of the lifespan the plot of log qjt for both samples 

 of mares is a presentable straight line with a doubling time of 

 3|-4 years (see Sacher, this colloquium, p. 115). The present 

 data are too poor for inference about its shape in stallions. 

 Most of the apparent gain in male survival occurs over the 

 years when mares may die of causes connected with foaling. 

 The only valid conclusion from the figures is that contrary to 

 the impression given by the uncorrected table (Comfort, 

 19596), stallions are not shorter-lived than mares under these 

 conditions of performance. 



