Test of Hypothesis

Surname 1
Student’s Name
Instructor’s Name
Course Name
Date
Test of Hypothesis
T-test
The ages of actresses when they won an acting award is summarized by the statistics n=78. x
with a line over it =35.2 years, and s=11.6 years. Use a 0.01 significance level to test the claim
that the mean age of actresses when they win an acting award is 34 years old
Hypothesis;
H0: = 34
H1: ≠ 34
T-statistics
Standard score, z=


Z=


Z=0.9136
P(X=34) = P(Z=0.9136) = 1.36
Z
α/2
=1.96
Surname 2
Since p(x=34) < Z
α/2
, do not reject H0 and conclude that the mean age of actresses when they
win an acting award is 34 years old
ANOVA
Suppose the National Transportation Safety Board (NTSB) wants to examine the safety of
compact cars, midsize cars, and full-size cars. It collects a sample of three for each of the
treatments (cars types). Using the hypothetical data provided below, test whether the mean
pressure applied to the driver’s head during a crash test is equal for each types of car. Use α =
5%.
A table of hypothetical data
Compact cars
Midsize cars
Full-size cars
643
469
484
655
427
456
702
525
402
666.67
473.67
447.33
s
31.18
49.17
41.68
Hypothesis
H0: µ
1
= µ
2
= µ
3
H1: At least one mean pressure is not statistically equal
T-statistics
Surname 3
Total sum of squares (SST)=
  


 where r is the number of rows in the table
and c is the number of columns in the table, is the grand mean and x
ij
is the i
th
observation in
the j
th
column.
Using the above data;
=

=

=529.22
SST= (643-529.66)
2
+(655-529.66)
2
+(702-529.66)
2
+(469-529.66)
2
+…+(402-529.66)
2
=96303.55
Treatment sum of squares (SSTR)=
  )^2
= [3*(666.67-529.22)
2
] + [3*(473.67-529.22)
2
] + [3*(447.33-529.22)
2
]
=86049.55
Error sum of squares(SSE)=
  ^2
= [(643-666.67)
2
+(655-666.67)
2
+(702-666.67)
2
] + [(469-473.67)
2
+(427-473.67)
2
+(525-
473.67)
2
] + [(484-447.33)
2
+(456-447.33)
2
+(402-447.33)
2
]
=10254
SST=SSTR+SSE (96303.55 = 86049.55 + 10254)
Total Mean Square (MST)=


where N is the total number of observations.
MST=


=12037.94
Mean Square Treatment (MSTR)=


Surname 4
MSTR=


=43024.78
Mean Square Error (MSE)=


MSE=


=1709
F=


=


=25.17
Critical value;
The degrees of freedom are given as df1 = 3 - 1 = 2 and df2 = 9 - 3 = 6. Given that α = 5%, from
the F tables, FCV 2,6 = 5.14
Decision Rule
Reject the null hypothesis if: F (observed value) > FCV (critical value). Since 25.17
> 5.14, we reject the null hypothesis.
Chi-square test
The table below shows the age distributions of women in the sample and all women in Toronto
between the ages of 20 and 44.
Age
Number in sample
Per cent in Census
20-24
103
18
25-34
216
50
35-44
171
32
Total
490
100
Surname 5
Using the data in the above table, conduct a chi square goodness of fit test to determine whether
the sample does provide a good match to the known age distribution of Toronto women. Use the
0.05 level of significance.
Hypothesis:
H0: The age distribution of respondents in the sample is the same as the age distribution of
Toronto women, based on the Census.
H1: The age distribution of respondents in the sample differs from the age distribution of women
in the Census.
The frequencies of occurrence of women in each age group are the observed values Oi presented
in the middle column of table above. There are k = 3 categories into which the data has been
grouped so that i = 1; 2; 3
Suppose the age distribution of women in the sample conforms exactly with the age distribution
of all Toronto women as determined from the Census. Then the expected values for each
category, Ei, can be determined. With these observed and expected numbers of cases, the
hypotheses can be rewritten as
H0 : Oi = Ei
H1 : Oi E
i
The test
For these hypotheses, the test statistic is
Χ
2
=


, with the degrees of freedom given as d=k-1
Surname 6
Let the 20-24 age group be category i=1. The 20-24 age group contains 18% of all the women,
and if the null hypothesis were to be exactly correct, there would be 18% of the 490 cases in
category 1. This is
E
1
=490x


=490x0.18=88.2
For the second category 25-34, there would be 50% of the total number of cases, so that
E
2
=490x


=490x0.5=245
E
3
=490x


=490x0.32=156.8
The table below shows the goodness of Fit Calculations for Sample of Toronto Women
O
i
E
i
O
i
-E
i
(O
i
-E
i
)
2
 

103
88.2
14.8
219.04
2.483
216
245.0
-29.0
841.00
3.433
171
156.8
14.2
201.64
1.286
490
490.0
0.0
7.202
Hence, Χ
2
=


=7.202
Critical value
Given that α=0.05 and the degrees of freedom, d=k-1=3-1=2, the critical value Χ
2
=5.991
Decision rule
Surname 7
Reject the null hypothesis if: Χ
2
(observed value) > Χ
2
i
(critical value). Since 7:202 > 5:991, we
reject the null hypothesis.
The statement of the author that the sample is a close match of the age distribution of all women
in Toronto is not exactly justified by the data presented in the first table.

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