A woman is beaten every 15 seconds.
This statement is sometimes attributed to the FBI, sometimes to the Bureau of Justice Statistics. You may find it attributed to other sources as well. The most common formulation is "According to the FBI..."
The FBI once did estimate that a woman is beaten every 15 seconds. However, the statement as used by feminist activists is a half-truth, and a very misleading one. First of all, the FBI does not calculate, tabulate, or track data on domestic violence. To make this estimate, the FBI used data from the book Behind Closed Doors: Violence in the American Family by Murray Straus, Richard J. Gelles, and Suzanne K. Steinmetz. The reason the statement as used by activists is a half-truth is that this book states that men and women are equally likely to be violent in relationships. The same data set that supports the claim "a woman is beaten every 15 seconds" also supports the claim that "a man is beaten every 15 seconds". The activists have made half of the data a rallying call for action, while suppressing or denying the other half of the same research.
Behind Closed Doors is based on data collected as part of the first National Family Violence study. These studies, funded primarily by the federal government, are currently conducted by the Family Research Laboratory at the University of New Hampshire. There have been two more of these studies since the book. All three are based on interviews with a randomly-selected sample of the population. This distinguishes them from police records and other "crime" data, which are necessarily based on the self-selected sample of those who come forward to report such violence.
All three National Family Violence studies, and in fact about 30 other similar studies done in other countries, have found that men and women are equally violent in relationships. Even when only interviews with women are taken into account, women themselves say they have engaged in more violent acts against their partners than the reverse. This is true even for the more serious forms of violence such as kicking, punching, or using a weapon to inflict injury.
You can verify this yourself. The paper entitled Change in Spouse Assault Rates from 1975 to 1992: A Comparison of Three National Surveys in the United States, which was presented at the 13th World Congress of Sociology, in Bielefeld, Germany, on July 19, 1994, may be ordered directly from the Family Research Laboratory by printing out the order form and sending it in with $2.00, plus shipping and handling. Order publication number V55.
It used to be fashionable at this point to say that because men are on average larger and physically stronger than women (though not obviously in all cases), women cannot do as much damage as men might in the same circumstances. However, other data suggests that women are four times more likely than men to use weapons in these attacks. A recent study reported in the Annals of Emergency Medicine and reviewed in the Journal of the American Medical Association states that half of the domestic violence injuries encountered in a large urban emergency room were sustained by men. These researchers stated that "19% of the women patients and 20% of the men had experienced recent physical violence." Significantly, these are almost exactly the same percentages found by the random-sample surveys such as those conducted by Straus, et.al.