Cipora, K. 1 & Wood, G. 2
1 Institute of Psychology. Jagiellonian University. Cracow, Poland.
2 Institute of Psychology. Karl-Franzens-University of Graz. Graz, Austria.
The SNARC (Spatial Numerical Association of Response Codes) effect is regarded as an index of the association of numbers and space. Although the SNARC effect has been consistently replicated, almost no studies reported between-groups differences. This led some to question the sensitivity of the SNARC effect to individual differences. Here we examined whether the lack of differences is due to poor estimation. The impact of sample size, number of repetitions per condition, and intraindividual variability on the probability of finding a non-zero SNARC effect was investigated. Simulations revealed that the most important factor determining the probability of detecting non-zero SNARC effect was the number of repetitions per condition. Moreover, very small sample sizes jeopardize the detection of SNARC, particularly when the number of repetitions is small. Therefore, failures to find significant between-groups differences is due foremost to lack of power to detect them, rather than to the absence of those differences. Fortunately, an adequate estimation of the SNARC effect is possible even with modest sample sizes when using 20 or more repetitions per condition. We conclude that the SNARC effect has the potential to reveal much more individual differences than what was reported before.