Calculating the Starting Sample Size for CAHPS Surveys
The starting sample size you need to achieve the desired number of completed CAHPS questionnaires for analysis and reporting should take several factors into account:
- The accuracy of the contact information.
- The mode or modes of data collection.
- Any prior surveys of the same or similar populations.
- Expectations about the number of individuals who may be identified as ineligible.
- The likely response rate among eligible individuals.
Inaccuracies in the sampling frame such as poor contact information (e.g., addresses and phone numbers) will decrease your response rate and need to be considered when estimating the starting sample size. In addition, an estimate of the proportion of the sample ineligible for the survey is needed to determine the total starting sample size.
The example below shows that a starting sample of 882 is needed to obtain 300 completed surveys if the response rate is 40% and the ineligible rate is 15%.
| Goal | 300 completed surveys |
|---|---|
| Anticipated response rate | 40 percent (= 0.40) |
| Minimum eligible sample needed | (300/0.40) = 750 patients |
| Ineligible rate | 15 percent |
| Eligible rate | 85 percent (= 0.85) |
| Total sample needed | (750/0.85) = 882 |
Read about Methods for Increasing the Number of Responses.
What if the patient base isn’t big enough for the required sample size? If a healthcare organization does not have a patient base large enough to draw the required sample size, the sample will be all patients who meet all the eligibility criteria. But even under these circumstances, the sample may include only one adult per household.
