Question

Professor Fair believes that extra time does not improve grades on exams. He randomly divided a...

Professor Fair believes that extra time does not improve grades on exams. He randomly divided a group of 300 students into two groups and gave them all the same test. One group had exactly 1 hour in which to finish the test, and the other group could stay as long as desired. The results are shown in the following table. Test at the 0.01 level of significance that time to complete a test and test results are independent.

Time A B C F Row Total
1 h 25 41 61 11 138
Unlimited 16 44 83 19 162
Column Total 41 85 144 30 300

(i) Give the value of the level of significance.


State the null and alternate hypotheses.

H0: The distributions for a timed test and an unlimited test are the same.
H1: The distributions for a timed test and an unlimited test are different.

H0: The distributions for a timed test and an unlimited test are different.
H1: The distributions for a timed test and an unlimited test are the same.   

H0: Time to take a test and test score are independent.
H1: Time to take a test and test score are not independent.

H0: Time to take a test and test score are not independent.
H1: Time to take a test and test score are independent.


(ii) Find the sample test statistic. (Round your answer to two decimal places.)


(iii) Find or estimate the P-value of the sample test statistic.

P-value > 0.100

0.050 < P-value < 0.100

   0.025 < P-value < 0.050

0.010 < P-value < 0.025

0.005 < P-value < 0.010

P-value < 0.005


(iv) Conclude the test.

Since the P-value ≥ α, we reject the null hypothesis.Since the P-value < α, we do not reject the null hypothesis.    

Since the P-value is ≥ α, we do not reject the null hypothesis.Since the P-value < α, we reject the null hypothesis.


(v) Interpret the conclusion in the context of the application.

At the 1% level of significance, there is insufficient evidence to claim that time to do a test and test results are not independent.

At the 1% level of significance, there is sufficient evidence to claim that time to do a test and test results are not independent.  

Homework Answers

Answer #1

i) value of the level of significance =0.01

H0: Time to take a test and test score are independent.
H1: Time to take a test and test score are not independent.

ii)

Applying chi square test:

Expected Ei=row total*column total/grand total A B C F Total
1 h 18.86 39.10 66.24 13.80 138
Unlimited 22.14 45.90 77.76 16.20 162
total 41 85 144 30 300
chi square    χ2 =(Oi-Ei)2/Ei A B C F Total
1 h 1.999 0.092 0.415 0.568 3.074
Unlimited 1.703 0.079 0.353 0.484 2.618
total 3.702 0.171 0.768 1.052 5.6924

sample test statistic =5.69

iii)

P-value > 0.100

iv) Since the P-value is ≥ α, we do not reject the null hypothesis

v)

At the 1% level of significance, there is insufficient evidence to claim that time to do a test and test results are not independent.

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