4. Forty percent of the women born in the 1970s will divorce. 

Yes, this is true.  Well mostly.  The number that is perhaps of most interest is the likelihood that a person's marriage will end in divorce. It is not possible to accurately estimate the number of marriages and divorces in a single year. The first thing to note is that this is always an estimate and like all estimates it can be wrong. Also, to arrive at this estimate, demographers calculate life tables that estimate the probability of divorce over a lifetime. Although this is a commonly reported statistic, it should be noted that it is based on some very shaky assumptions. The main assumption being that the likelihood of divorce for today's young married person will follow the same pattern as previous generations. Now this is reasonable assumption, but it could be wrong. Another thing to keep in mind about probability of divorce estimates is that they vary by the age of the person. The probability of divorce for a 20-year-old is not the same as a 40-year-old. The 40-year-old has less of a chance of divorce.