From the 2017 National Survey on Drug Use and Health, the prevalence of major depressive episodes among adults in the United States is estimated to be 7.1%. Suppose that 2,250 adults were randomly selected for a new study on testing the effectiveness of a new treatment.
(Source: U.S. Department of Health and Human Services. Major Depression. National Institute of Mental Health. https://www.nimh.nih.gov/health/statistics/major-depression.shtml)
What is the expected value for the proportion of those suffering from depression for our sample, based on what we know about the population proportion?