Final answer:
To estimate the proportion of the adult population with high blood pressure, a researcher needs to determine the sample size based on desired confidence level and margin of error.
Step-by-step explanation:
To estimate the proportion of the adult population of the United States that has high blood pressure, the researcher needs to determine the sample size. The sample size needed depends on the desired confidence level and the margin of error. If the researcher wants to be 99% confident that the estimated proportion is within a certain range, they would need a larger sample size compared to a lower confidence level. A larger sample size reduces the margin of error and increases the precision of the estimate.