Statistical modelling/Milk consumption & marketing

The standard errors for total milk offtake (0.6 and 1.2, respectively, in the table on the previous page) were estimated by using the residual mean square 0.3210 for milk offtake in the final analysis of variance table in the GenStat regression analysis output, dividing by the number of cows used in the analysis, and multiplying by the average number of lactating cows per household. Thus:

11.5 x (0.3210/111)  = 0.6 for Bilisa
15.4 x (0.3210/53)    = 1.2 for Assa.

Although family sizes were similar in Bilisa and Assa there was a large difference in recorded milk consumption in the home (an apparent 4.8 litres per day in Bilisa and 12.8 litres per day in Assa). Dividing the average quantity consumed by the average size of the family size gives about 0.3 litres per household member in Bilisa and about 0.8 litres in Assa. The difference is surprising.

But the quantities unaccounted for in the table are:

for Bilisa:     21.2 - 4.8 -1.2 - 2.2 = 12.8 litres
for Assa:     15.6 -12.8 -1.1 - 0.2 = 1.5 litres