Question

A school psychologist notes that the average number of times that students are disruptive during class is 1.4 [μ=1.4] times per day. Following recent classroom policy changes, the psychologist tests if the number of disruptions during class has changed. He records the following number of disruptions observed during a class day: 2, 4, 3, 5, 1, 1, and 4.

A. Test the hypothesis that the number of complaints has increased or decreased using a .05 level of significance.
B. Compute effect size using estimated Cohen's d.

Answer 1

Reject the Null ;

0.928

Explanation:

Given the data: 2, 4, 3, 5, 1, 1, 4

Sample mean = (2 + 4 + 3 + 5 + 1 + 1 + 4) / 7 = 2.857

Standard deviation, s = 1.57 ( using calculator)

The hypothesis :

H0 : μ = 1.4

H1 : μ ≠ 1.4

Since sample size is small, use T test

Test statistic :

Tstatistic = (x - μ) / s/sqrt(n)

Tstatistic = (2.857 - 1.4) / 1.57/sqrt(7)

Tstatistic = 1.457 / 0.593 = 2.455

Two tailed test at α = 0.05

Tcritical at df = 7-1 = 6 ; α = 0.05 = 2.447

Tstatistic > Tcritical ; reject the null

Since ;

2.455 > 2.447 ; we reject the null ;

There is significam evidence that Number of complaints has changed.

Effect size ;

d = (x - μ) / s

d = (2.857 - 1.4) / 1.57

d = 1.457 / 1.57

d = 0.928