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    Comparison of ANOVA F and WELCH Tests with Their Respective Permutation Versions in Terms of Type I Error Rates and Test Power
    (Kafkas Univ, Veteriner Fakultesi Dergisi, 2010) Mendes, Mehmet; Akkartal, Erkut
    We compared Analysis of Variance (F) and the Welch test (W) with their respective permutation versions (PF and PW) in terms of Type I error rate (alpha) and test power (1-beta) by Monte Carlo simulation technique. Simulation results showed that when the variances were homogeneous, the permutation versions of F and W tests displayed more reliable results in terms of protecting Type I error rate at nominal level, regardless of distribution shape and sample size. Violation of homogeneity of variances adversely affected all tests. Regardless of sample size and effect size, the PF test was slightly more powerful compared to the F test as long as the variances were homogeneous and the distributions were skewed (chi(2)(3) and Exp [0.75]). The PF and F tests had similar power levels when the distributions were symmetrical (Beta (5.5)). The W test was more powerful with homogenous variances, while the PW test was slightly superior with heterogonous variances except for unbalanced sample sizes (i.e., 5:10:15).
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    Determination of suitable permutation numbers in comparing independent group means: a monte carlo simulation study
    (Natl Inst Science Communication-Niscair, 2010) Akkartal, Erkut; Mendes, Mehmet; Mendes, Emel
    In this study, suitable number of permutations were tried to be determined empirically for permutation test, one of which lalternatively used in analysis of variance (ANOVA). Random numbers were generated from chi(2) (3). distribution by simulation technique, and type 1 error rates were calculated with their standard errors. For k=2, 3 and 4, data were dealt with what is commonly faced in practice. Number of observation (n) in each group were taken to be 5, 10 and 15 (except for k = 2). Number of permutation changes with respect to k and n. For k=2, 3 and 4, required number of permutation was determined to be 15,000, 25,000 and 30,000 respectively. In general, there is great advantage of not allowing number of permutation under 10,000, if permutation tests are to be used in testing significance of differences of means of groups.
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    Regression tree analysis for predicting slaughter weight in broilers
    (Taylor & Francis Ltd, 2009) Mendes, Mehmet; Akkartal, Erkut
    In this study, Regression Tree Analysis (RTA) was used to predict and to determine the most important variables in predicting the slaughter weight of Ross 308 broiler chickens. Data for this study came from 224 chickens raised during three different seasons, namely spring (n=66), summer (n=66), winter (n=92). Second week body weight, shank length, shank width, breast bone length, breast width, breast circumference and body length were used to predict the slaughter weight. Results of RTA showed that among the seven independent variables only four were selected, namely; body weight, breast bone length, shank width, and breast circumference. These selected independent variables were more efficient than the others in predicting the slaughter weight. RTA indicated that the birds which had values of second week body weight >= 295.95 g, breast bone length >55.82 mm and breast circumference >14.18 cm or that of body weight <= 295.95 g, breast bone length >60.26 mm and shank width >8.32 mm could be expected to have higher slaughter weights.