Psychological tests such as the WCST, administered alone, cannot be used to measure the effects of a frontal lobe injury, or the aspects of cognitive function it may affect, such as working memory; a variety of tests must be used. A subject may be good at one task but show dysfunction in executive function overall. Similarly, test results can be made misleading after testing the same individual over a long period of time. The subject may get better at a task, but not because of an improvement in executive cognitive function. They may have simply learned some strategies for doing this particular task that made it no longer a good measurement tool.