The study was done on West German men and women between the ages of 36-55, with the average male respondent being somewhat younger than the average female respondent; and they are slightly ambiguous about how TFR was calculated, saying at one point that they used birth certificates and at another that they used children resident in the household. Whether they used birth certificates or residential data, there is a little problem; a newborn's mother is always known and usually raises him, whereas the father not so much. In either kind of calculation, the "fertility" of women will always be higher than the "fertility" of men, simply because some children are born fatherless or raised by single mothers. But I don't think that is even necessarily the problem; because German men are three years older than German women at the birth of their first child (and presumably, on average, at the births of higher-order children as well), some of the older women in the sample have husbands who were too old to be included in the sample, while some of the younger men in the same have wives who were too young to be included (or haven't settled down yet in the first place). It's also possible that some of the fathers were *East* rather than West German, due to internal mobility, but I suspect the age effects explain most of the effect.