Imagine we conduct a study to determine how long it takes salesclerks to approach and help hearing-disabled customers. If differences do emerge between these two IV levels, can we say confidently that the differences are due to deafness, or might there be another variable at play (like chance) that better accounts for any observed differences? As your Pause-Problem, think of two factors that account for why helping times might differ between conditions (other than deafness vs. hearing)