Which source is most appropriate for assessing behavior level in Kirkpatrick's evaluation model?

The most appropriate source for assessing behavior level in Kirkpatrick's evaluation model is a performance appraisal conducted on trainees 6 months after they return to work. This is because the behavior level evaluates how well trainees apply what they learned during training in their actual work environment. A performance appraisal conducted at this point provides a comprehensive assessment of an individual’s performance on the job, focusing on observable behaviors and outcomes that result from the training.

By waiting 6 months, the performance appraisal allows enough time for the trainees to implement their new skills and knowledge, making it possible to evaluate whether their behavior has changed as a result of the training. This time frame provides a clearer picture of long-term retention and application of skills, rather than immediate reactions or feelings about the training process.

In contrast, surveys filled out by the trainees might capture their perceptions and feelings about the training but do not directly assess behavioral changes. Feedback from supervisors at the start of training is premature because it occurs before any behavioral application can be observed. Lastly, training completion rates indicate whether trainees finished the program but do not measure how effectively they apply learned behaviors in the workplace. Thus, a performance appraisal conducted after a suitable duration post-training is the best method for assessing behavior in this context.