Question

A psychologist would like to examine the effect of fatigue on mental alertness. An attention test is prepared which requires subjects to sit in front of a blank TV screen and press a response button each time a dot appears on the screen. A total of 110 dots are presented during a 90-minute period, and the reach subject. Two groups of subjects are selected. The first group (n 5) is tested after they have been kept awake for 24 hours. The second group (n-10) is tested in the morning after a full night's sleep. The data for these two samples are as follows:

Awake 24 hours rested
x=35 X=24
ss=120 ss =360
On the basis of these data, can psychologist conclude that fatigue significantly increases errors on an attention task? Test with α-05 and report effect size.

Answer 1

The calculated value of t= 0.1908 does not lie in the critical region t= 1.77 Therefore we accept our null hypothesis that fatigue does not significantly increase errors on an attention task at 0.05 significance level

Explanation:

We formulate null and alternate hypotheses are

H0 : u1 < u2 against Ha: u1 ≥ u 2

Where u1 is the group tested after they were awake for 24 hours.

The Significance level alpha is chosen to be ∝ = 0.05

The critical region t ≥ t (0.05, 13) = 1.77

Degrees of freedom is calculated df = υ= n1+n2- 2= 5+10-2= 13

Here the difference between the sample means is x`1- x`2= 35-24= 11

The pooled estimate for the common variance σ² is

Sp² = 1/n1+n2 -2 [ ∑ (x1i - x1`)² + ∑ (x2j - x`2)²]

= 1/13 [ 120²+360²]

Sp = 105.25

The test statistic is

t = (x`1- x` ) /. Sp √1/n1 + 1/n2

t= 11/ 105.25 √1/5+ 1/10

t= 11/57.65

t= 0.1908

The calculated value of t= 0.1908 does not lie in the critical region t= 1.77 Therefore we accept our null hypothesis that fatigue does not significantly increase errors on an attention task at 0.05 significance level