Question

The student welfare office was interested in trying to enhance students’ exam performance by investigating the effects of various interventions. They took five groups of students before their statistics exams and gave them one of five interventions: (1) a control group just sat in a room contemplating the task ahead; (2) the second group had a yoga class to relax them; (3) the third group were told they would get monetary rewards contingent upon the grade they received in the exam; (4) the fourth group were given beta-blockers to calm their nerves; and (5) the fifth group were encouraged to sit around winding each other up about how much revision they had/hadn’t done (a bit like what usually happens). The final percentage obtained in the exam was the dependent variable. Using the critical values for F, how would you report the result in the table below?

	SS	Df	MS	F
Model	1213.6	4	303.4	12.43**
Residual	707.9	29	21.4
Total	1921.5	33

	a.	Type of intervention had a significant effect on levels of exam performance, F(4, 29) = 12.43, p < .01.
	b.	Type of intervention did not have a significant effect on levels of exam performance, F(4, 29) = 12.43, p > .05.
	c.	Type of intervention did not have a significant effect on levels of exam performance, F(4, 33) = 12.43, p > .01.
	d.	Type of intervention had a significant effect on levels of exam performance, F(4, 33) = 12.43, p < .01.

I don't understand how to find the critical F value, embarrassingly. I know there is a chart in the back of the book, but I am a little lost on how to find it so that I can solve this problem.

Answer 1

Here,

n1=4, n2=29, =0.01⇒1-=0.99

using excel,

=F.INV(0.99,4,29)=4.044873

and p-value=0.00001<

i.e.

a)Type of intervention had a significant effect on levels of exam performance, F(4, 29) = 12.43, p < .01.