R. Bras. Zootec.01/Apr/1999;28(2):279-87.
Estimate of sample size in repeated measurements of scrotal circumference of Nellore cattle
DOI: 10.1590/S1516-35981999000200010
The objective of this work was to estimate minimum sample size (n) of animals to detect significant differences (D) among monthly replicate evaluations of scrotal circumference from animals of the Nellore breed, from 10 to 30 months of age, considered as 21 evaluation conditions or repeated measurements (treatments). The value of n that allows to detect the D among means when each subject is observed for t > 2 treatments, was obtained by means of the Statistical Analysis System – SAS developed program, the t-variate normal distribution (t=21), as a vector of zero mean and S covariate matrix, Hotelling T2 statistics and F-distribution with noncentrality parameter of d2D. Different levels of type I error (a), power of the test (1- b), minimum correlation among repeated measurements (rmin) and D were considered. The n estimates ranged from 4 to 299, being mostly affected by changes in the D.