Several apparently contradictory models predicting critical conditions for chain entanglement in flexible polymers have appeared in recent years. Some models predict entanglement molecular weight to increase, and others to decrease, with chain stiffness. Literature data are used here to compare model predictions. An inverse correlation between characteristic ratio and segmental aspect ratio is found, allowing the contradiction to be resolved. In flexible chains, it is found that the aspect ratio of a Kuhn step length is approximately independent of molecular characteristics and that stiffness depends more strongly on segmental aspect ratio than on characteristic ratio.