Authors: Zahide KOCABAŞ, Tahsin KESİCİ, Ayhan ELİÇİN
Abstract: Weekly body weights from approximately 10 weeks of age to 19-29 weeks of age were used to study growth curve in Akkaraman, Ivesi x Akkaraman and Malya x Akkaraman lambs. A linear model was fitted to means of body weights using age as independent variable. The linear model provided a good fit with R2 values of 99%, 99.3% and 98.9% for Akkaraman, Ivesi x Akkaraman and Malya x Akkaraman, respectively. Afterthat, a common regression coefficient was calculated as within lambs regression coefficient, which gave R2 values of 95.9%, 97% and 95.8% for Akkaraman, Ivesi x Akkaraman and Malya x Akkaraman lambs, repectively. However, test of homogeneity of regression coffecient verified that there was an evidence of a statistically significant diversity of regression coefficients fitted to each lamb, which means that the growth pattern of all lambs cannot be represented by a common regression equation. Moreover, the data were analyzed considering several measurement on body-weight at each time point. In this way, residual sum of squares was divided into two parts: pure error from repeated measurements and lack of fit sum of squares. This method led to a decline in R2 values, which were 79.1%, 91.7% and 88.4% for Akkaraman, Ivesi x Akkaraman and Malya x Akkaraman lambs, respectively.
Keywords: Linear model, common regression, homogeneity of regression, pure error, lack of fit, lambs