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Briefly, this special type of regression models the data in terms of leaving tendency (so-called hazard rate), which is the probability per unit of time that a female leaves the patch given that she is still on it. This leaving tendency can be modified by some predefined explanatory factors (i.e. covariates) according to the following equation: (eqn http://www.selleckchem.com/products/Trichostatin-A.html 1) in which h(t) is the hazard rate, h0(t) is the innate patch-leaving tendency (so-called baseline hazard), t the time passed since the female entered the patch, and ��i the regression coefficients that give relative contributions of p covariates zi. The relative contribution of the covariates can be interpreted through the exponential term (so-called hazard ratio). A hazard ratio greater than one indicates an increasing effect of the associated covariate on the females�� patch-leaving tendency, while a hazard ratio lower than one will be interpreted in the opposite way. The effects of the number of sons and daughters laid by the females http://www.selleckchem.com/products/pd-0332991-palbociclib-isethionate.html on their patch-leaving decision were tested in the model as two time-dependant covariates, while the initial size of patch was added as a fixed categorical covariate. The experimental protocol used generated a small number of missing values due either to pre-adult mortality of the developing wasps or to superparasitism events (in 76 and 37 cases of the 1490 host attacks observed, respectively). In these cases, the sex of the missing progeny was estimated by the average sex ratio observed at the corresponding rank of oviposition. Hence, the Cox regression model used in this study was sometimes http://www.selleck.cn/products/ve-822.html based on two events appearing simultaneously, coded as the probability of laying a son or a daughter, respectively. Regression coefficients of the model were estimated from the data by partial likelihood maximization, and the significance of the covariates was tested using standard likelihood ratio tests through an iterative procedure. Finally, the fit of the model was assessed by making residual plots (see Wajnberg, Rosi & Colazza 1999 for an example of such a plot). All computations were performed in S-Plus (Venables & Ripley 1994). Trichogramma chilonis females stayed longer on patches containing initially a higher number of hosts (Fig.?1a), but their final rates of progeny production remain statistically similar, whatever the initial quality of the patch they were offered (Fig.?1b). Thus, at first glance, their patch exploitation strategy seems to be consistent with the optimal predictions of the MVT. Fitting a Cox regression model to the data revealed that the patch-leaving tendency of the females depends on the initial quality of the patch the females were foraging on (likelihood ratio test: ��2?=?152��72, 2 d.f., P?