Which of the following assumptions concerning the probability distribution of the random error term in a simple regression model is stated incorrectly? a. the distribution is normalb. the mean of the distribution is 0c. the errors are not independentd. the variance of the distribution is constantthe probability that a person tested positive on a screening test given that he/she has a disease is called the: a. negative predicitive valueb. positive predicitive valuec. sensitivityd. specificity