one tailed tests

Question

A physics professor is experiencing an attendance problem because physics, is like, super hard. His classes tend to average 107 overall absences per semester with a standard deviation of 17. He decides to make attendance a major part of the class grade and over the next 9 semesters he finds he had an average of 86 absences. Was his new class policy successful in reducing the number of absences?

a. What are the groups?

What is the dependent variable?

b. What are the null and research hypotheses?

c. What are the numbers needed to compute the formula?

d. What is the z statistic?

e. For a one tailed test at .05 significance, the critical value is 1.65. What decision do we make?

f. What is the effect size? (M-μ/σ)

Answer 1

a. class averages before policy and after policy

dependent variable is number of absences

b. Ho: average = 107

Ha: average < 107

c. before policy change mean and standard deviation, after policy change mean, sample size (number of semesters)

d. (sample mean - before policy change mean)/(before policy standard deviation/square root(sample size))

z = (86 - 117)/(17/sqrt(9)) = -5.47

e. reject Ho (z < -critical value)

f. (86 - 117)/17 = -1.82