Technical note: prediction of sex based on five skull traits using decision analysis (CHAID).

Osteologists commonly assess the sex of skeletal remains found in forensic and archaeological contexts based on ordinal scores of subjectively assessed sexually dimorphic traits. Using known-sex samples, logistic regression (LR) discriminant functions have been recently developed, which allow sex probabilities to be determined. A limitation of LR is that it emphasizes main effects and not interactions. Chi-square automatic interaction detection (CHAID) is an alternative classification strategy that emphasizes the information in variable interactions and uses decision trees to maximize the probability of correct sex determinations. We used CHAID to analyze the predictive value of the 31 possible combinations of five sexually dimorphic skull traits that Walker used previously to develop logistic regression sex determination equations. The samples consisted of 304 individuals of known sex of English, African American, and European American origin. Based on practical considerations, selection criteria for the best sex predictive trait combinations (SPTCs) were set at accuracies for both sexes of 75% or greater and sex biases lower than 5%. Although several of the trees meeting these criteria were produced for the English and European American samples, none met them for the African American sample. In the series of out-of-sample tests we performed, the trees from the English and combined sample of all groups predicted best.

Reproductive measures, fitness, and migrating Mennonites: an evolutionary analysis.

Given the same reproductive span, more children with shorter interbirth intervals and less parental attention per child should not do as well. There should be intermediate optima in family sizes, but only two studies have demonstrated optima. The goal here is to determine whether the relationship between fitness and fertility is linear and whether this relationship masks underlying variation in reproductive behaviors in a Mennonite congregation that lived in two disease settings, Prussia/Russia vs. Kansas. The relationships between children born and fitness were determined by calculating linear and quadratic regressions for total, Prussia/Russia vs. Kansas, and families with deaths vs. families with no deaths for total, Prussia/Russia, and Kansas. Variation was examined in terms of measures of reproductive success and reproductive span. Comparisons were made by t tests with Bonferroni correction. Regressions demonstrate equally well that the more children women bear, the higher the reproductive success, whether in the harsher disease ecology of rural Prussia/Russia or in less challenging rural Kansas and whether the women experience deaths or not. Prussian/Russian mothers bore significantly more children (6.5+/-0.3) than Kansan mothers (5.6+/-0.2) over longer reproductive spans but did not significantly increase the number of surviving children (4.9+/-0.2 vs. 4.7+/-0.2, respectively). Families experiencing deaths vs. no deaths exhibit significantly longer reproductive spans, reflecting a significantly earlier start at childbearing and a later finish, and produce significantly more children (5.4+/-0.2 vs. 4.2+/-0.2). Cox regressions were run, and the most significant covariates to negatively affect survivorship to 15 years were death in the family and length of the previous interbirth intervals. There was variation in families, but perhaps most had adequate nutrition, which may explain the lack of optima in fitness.