Different sources note different incidences of side effects. The most common side effect is breakthrough bleeding. A 1992 French review article said that as many as 50% of new first-time users discontinue the birth control pill before the end of the first year because of the annoyance of side effects such as breakthrough bleeding and amenorrhea. A 2001 study by the Kinsey Institute exploring predictors of discontinuation of oral contraceptives found that 47% of 79 women discontinued the pill. One 1994 study found that women using birth control pills blinked 32% more often than those not using the contraception.