Countering these studies are other works that have identified the Ape Index as a significant (or potentially significant) factor. A 2001 study comparing teenage male and female rock climbers noted that performance differences between the genders could be explained by a number of factors, one of which was the lower Ape Index found in the female climbers. Similarly, in a later work it was found that the Ape Index was statistically significant, and thus determined that it was one of a number of variables that provided the highest diagnostic value in the prediction of climbing performance.