The present study examined whether any unconsidered variable during revision of the K-WAIS would lower reliability of its standardized score.

In this study, a group of participants were assigned to perform modified ‘coding’ tests, respectively. To avoid the norm group issue, all the conditions except the stimuli were set identical across the tests. Analysis focused on finding variables which would contribute to difference among the tests, including their distribution patterns.

The results showed that physical differences of spatial organization across the tests and background such as figure shapes attributed to significant difference between ‘digit symbol’ in K-WAIS and ‘coding’ in K-WAIS-IV.

It suggests possibility of different difficulty level between ‘digit symbol’ in K-WAIS and ‘coding’ in K-WAIS-IV. Analysis of performance distribution also indicates that the test with better performance (K-WAIS coding) may have lower difficulty because its score distribution was more negatively skewed than that of the other.