In: Statistics and Probability
"Durable press" cotton fabrics are treated to improve their
recovery from wrinkles after washing "Wrinkle recovery angle"
measures how well a fabric recovers from wrinkles. Higher is
better. Here are data on the wrinkle recovery angle (in degrees)
for the some fabric specimens.
Permafresh | Hylite |
124 | 147 |
104 | 199 |
142 | 149 |
111 | 156 |
123 |
A consumer group suspects that there is a difference in recovery
from wrinkles after washing. Specifically, they want to test the
claim that there is a difference in recovery between using
Permafresh and Hilite. To investigate this, they identified the
mean recovery from wrinkles after washing by measuring the wrinkle
recovery angle in degrees for a sample of fabrics using Permafresh,
and a sample of fabrics using Hylite.
At the 5% level of significance, is there enough evidence to
conclude that there is a difference in wrinkle recovery angle
between Permafresh and Hylite?
It is often reasonable to conclude that measurements are normal in
distribution. So it is reasonable to assume the population of
wrinkle recovery angle is normal for both Permafresh and Hylite.
Also assume that the data represents a SRS (simple random sample)
of fabrics using Permafresh and Hylite.
1) Why is this a two sample independent means test? and
Step 1: State the Claims which means to State the
null and alternative hypotheses. Use correct math type. You may
want to consider looking back at the symbols assignment from the
beginning of class.
using excel>addin>phstat>two sample test
we ahve
Pooled-Variance t Test for the Difference Between Two Means | |
(assumes equal population variances) | |
Data | |
Hypothesized Difference | 0 |
Level of Significance | 0.05 |
Population 1 Sample | |
Sample Size | 5 |
Sample Mean | 120.8 |
Sample Standard Deviation | 14.51551 |
Population 2 Sample | |
Sample Size | 4 |
Sample Mean | 162.75 |
Sample Standard Deviation | 24.47277 |
Intermediate Calculations | |
Population 1 Sample Degrees of Freedom | 4 |
Population 2 Sample Degrees of Freedom | 3 |
Total Degrees of Freedom | 7 |
Pooled Variance | 377.0786 |
Standard Error | 13.0263 |
Difference in Sample Means | -41.9500 |
t Test Statistic | -3.2204 |
Two-Tail Test | |
Lower Critical Value | -2.3646 |
Upper Critical Value | 2.3646 |
p-Value | 0.0146 |
Reject the null hypothesis |
Here claim is that there is a difference in wrinkle recovery
angle between Permafresh and Hylite.
It is often reasonable to conclude that measurements are normal in
distribution. So it is reasonable to assume the population of
wrinkle recovery angle is normal for both Permafresh and Hylite.
Also assume that the data represents a SRS (simple random sample)
of fabrics using Permafresh and Hylite.
1) this is a two sample independent means test because two sample
teken for this scenario is independent and taken with Simple random
sampling and also the population from which these samples are drawn
is given to normal. so it satisfy all the conditionfor independent
sample t test
Step 1: the Claim is is that there is a difference in wrinkle recovery angle between Permafresh and Hylite
the null and alternative hypotheses are
Ho: u( Permafresh) = u(Hylite)
Ha: u( Permafresh) ≠ u(Hylite)
the value of test stat t = -3.2204
p value is 0.0146
since p value is less than 0.05 so we reject Ho and conclude that there is a difference in wrinkle recovery angle between Permafresh and Hylite