In each situation, explain whether the value given in bold print is a statistic or a parameter:
a. A polling organization samples 1000 adults nationwide and finds that 72% of those sampled favor tougher penalties for persons convicted of drunk driving.
b. In the year 2000 census, the U.S. Census Bureau found that the median age of all American citizens was about 35 years.
c. For a sample of 20 men and 25 women, there is a 14-cm difference in the mean heights of the men and women.
d. A writer wants to know how many typing mistakes there are in his manuscript, so he hires a proofreader, who reads the entire manuscript and finds 15 errors.