In many studies, EEG measures reflect performance in visual and cognitive tests, as determined by averages across different conditions or groups of participants. Based on these results, one might expect that there is also a significant correlation between performance and EEG measures at the individual level. In this study, we tested young and older adults with three visual tests while recording EEG. We analyzed 13 EEG measures, which were shown to reflect specific aspects of visual processing. Surprisingly, correlations between visual performance and the EEG measures were weak. Even more surprisingly, the EEG measures were highly correlated within participants. Our findings suggest that commonly used EEG measures mainly represent stable traits of participants rather than performance in the tests.