Final answer:
Nonresponse bias may have an impact on the confidence interval, but is not accounted for by the margin of error.
Step-by-step explanation:
The factor that may have an impact on the confidence interval but is not accounted for by the margin of error is nonresponse bias.
Nonresponse bias occurs when the individuals who do not respond to the survey have different characteristics than those who do respond, resulting in a biased sample. This can impact the estimated mean number of billable hours for all employees in the company.
To account for nonresponse bias, Sam could consider implementing strategies to encourage more employees to respond to the survey or use statistical techniques to adjust for potential bias in the sample.