Abstract
Influence of the ability distribution skewness on the distribution of statistic lz. The appropriateness measurement statistic lz of Drasgow, Levine & Williams (1985) is a suitable index for detecting aberrant patterns because of its high hit rates. However, the normal distribution of this index is affected, for instance, by the test length, the item response model or the ability distribution. This research analyses the effect of the ability distribution skewness on the distribution of lz, and the test length, the extent of the discrimination parameter and the estimation process of the ability and items are also manipulated. The results show that the distribution of the index lz is aproximately a normal distribution but skewed and sightly leptokurtic; the false positive rates point out that the index lz is a conservative and consistent test in the significance level of .05.
