On Estimating the Population of Aphids in A Potato Field

This appendix to the preceding paper by L. Broadbent deals with the statistical problem of estimating the population of aphids per plant in a field of growing potatoes. An unbiased method is described, in which a definite proportion of a number of plants is sampled, and also a more rapid, method of stratified sampling. (An account of the statistical principles involved has been given by Yates (1946).) Sampling for purposes of inspection is then considered, using practices current in industrial statistics and described, for example, by Peach (1947). Finally, some counts on Myzus persicae are examined, to obtain information on the. type of variation in aphid numbers to be expected.