Power and speed components of individual differences in letter matching

Several previous studies have reported a correlation (typically around -.30) between standardized verbal ability test scores and name identity minus physical identity reaction times (NI-PI) in a letter-matching task. This correlation has usually been thought to reflect the mutual dependence of both measures on long-term memory access time. The present research was designed to assess Carroll's (1981) suggestions that: (a) NI - PI may not be the optimal formula for predicting standardized test scores from letter matching data, and (b) NI - PI may actually be related to the speed rather than the power component of standardized tests. Fifty-one subjects previously tested with a standardized reading test participated in letter-matching and word-reading tasks. The latter tasks required subjects to read words and specially constructed pseudowords. Power and speed measures were derived from the word-reading tasks and the standardized test on theoretical grounds (and supported by a principal components analysis). The results supported both of Carroll's contentions. NI - PI reaction time was related more to speed than power and the NI - PI statistic (as usually used) was not the optimum formula for predicting standardized test scores.