Suppose that people usually lost about 15 pounds when they are on a diet for six months, with a standard deviation of 4 pounds. A sample of 20 adults (10 males and 10 females) enrolled in a weight control program. The mean weight loss for the sample is 16 pounds after six months.

• With the following question is the sample representative of the population with respect to the number of pounds lost? If so, why? If not, why?

• I know that I am supposed to run a z-test. What is the exact formula?
• Is the Cohen's d effect size small, moderate, or large?
• I am double checking my homework