Question

In: Statistics and Probability

Two brands of microwave popcorn are compared for consistency in popping time.  The popping times, in seconds,...

Two brands of microwave popcorn are compared for consistency in popping time.  The popping times, in seconds, for 30 randomly selected bags of each brand are provided in the attached file ‘Popcorn’.  Use the technology of your choice to answer the following questions.

a. We are interested in determining whether the standard deviations of the popping times differ for the two brands of popcorn. Conduct an appropriate analysis of the data values and determine if the assumptions of the F-Test procedure for testing the equality of variances are satisfied.

b. Conduct an F-test for the equality of the standard deviations of the two brands. Are the standard deviations different at the 0.01 significance level?

Construct a 99% confidence interval for the ratio of the standard deviations. Which of the following statements is true?

The confidence interval includes the value zero (0) which indicates there is no difference in the standard deviations.

The confidence interval includes the value zero (0) which indicates there is a difference in the standard deviations.

The confidence interval includes the value one (1) which indicates there is no difference in the standard deviations.

The confidence interval includes the value one (1) which indicates there is a difference in the standard deviations.

BRAND_A BRAND_B
147 146
150 152
151 153
139 150
165 146
153 152
154 154
158 141
146 157
153 149
145 152
142 150
158 158
145 143
143 150
157 148
155 149
138 150
147 141
147 145
153 149
164 147
140 158
155 143
151 158
144 154
146 145
151 149
160 152
147 158

Solutions

Expert Solution

a) Assumptions:

Population is approximately normal.

Samples are independent and random.

b) Brand A, Sample 1:  
Sample standard deviation, s₁ = STDEV.S() = 7.0110
n₁ =    30
Brand B, Sample 2:  
s₂ =    4.9861
n₂ =    30
α =    0.01
  
Null and alternative hypothesis:  
Hₒ : σ₁ = σ₂  
H₁ : σ₁ ≠ σ₂  
  
Test statistic:  
F = s₁² / s₂² = 1.9772
  
Degree of freedom:  
df₁ = n₁-1 =    29
df₂ = n₂-1 =    29
  
Critical value(s):  
Lower tailed critical value, Fα/2 = F.INV(0.005, 29,29) =  0.3740
Upper tailed critical value, F1-α/2 = F.INV(0.995, 29,29) =   2.6740
  
P-value :  
P-value = 2*F.DIST.RT(1.9772, 29, 29) =   0.0714

Decision: Do not reject the null hypothesis.

99% confidence interval for standard deviation:

Lower Bound = SQRT((s₁² / s₂²)/F₁-α/₂) = 0.8599
Upper Bound = SQRT((s₁² / s₂²)/Fα/₂) = 2.2993

The confidence interval includes the value one (1) which indicates there is no difference in the standard deviations.


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