6. The t test for two independent samples one-tailed example using tables Aaa Aa
ID: 3218688 • Letter: 6
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6. The t test for two independent samples one-tailed example using tables Aaa Aa Most engaged couples expect or at least hope that they will have high levels of marital satisfaction. However because 54% of first marriages end in divorce, social scientists have begun investigating influences on marital satisfaction. [Data source: This data was obtained from National Center for Health Statistics.] Suppose a counseling psychologist sets out to look at the role of economic hardship in relationship longevity. He decides to measure marital satisfaction in a group of couples living above the poverty level and a group of couples living below the poverty level. He chooses the Marital Satisfaction Inventory, because it refers to "partner" and "relationship" rather than "spouse" and "marriage," which makes it useful for research with both traditional and nontraditional couples. Higher scores on the Marital Satisfaction Inventory indicate greater satisfaction. There is one score per couple. Assume that these scores are normally distributed and that the variances of the scores are the same among couples living above the poverty level as among couples living below the poverty level The psychologist thinks that couples living above the poverty level will have greater relationship satisfaction than couples living below the poverty level. He identifies the null and alternative hypotheses as 0 H couples living above the poverty level Hcouples living below the poverty level 1: H Hcouples living below the poverty level couples living above the poverty level This is a tailed test The psychologist collects the data. A group of 39 couples living above the poverty level scored an average of 51.1 with a sample standard deviation of 9 on the Marital Satisfaction Inventory. A group of 31 couples living below the poverty level scored an average of 45.2 with a sample standard deviation of 12. Use the t distribution table. To use the table, you will first need to calculate the degrees of freedom. The degrees of freedom are To see the table, click on the arrow and then on the words "The t distribution" that appear in the space belowExplanation / Answer
null hypothesis
Ho = µcouples living above the poverty level = µcouples living below the poverty level
Alternate hypothesis:
H1 = µcouples living above the poverty level > µcouples living below the poverty level
This is a one tailed test.
Above poverty line:
n1 = 39 X1 = 51.5 , s1 = 9
below poverty line:
n2 = 31 X2 = 45.2 , s2 = 12
degrees of freedom = n1 + n2 -2 = 39+31-2 = 68
t-score with d.f as 60 = 1.671
t-score with d.f as 80 = 1.664
1.671-1.664 = 0.007
0.007/20=0.00035
0.00035*8= 0.0028
critical t-score with d.f as 68 = 1.671-0.0028 = 1.6682
pooled variance=Sp2 = [(n1-1)s12 + (n2-1)s22 ]/( n1 + n2 -2)
= [38*81 + 30*144]/68
=108.7941
Standard error = Sp* [(1/n1)+(1/n2)]
= 10.4304(0.057899)
=10.4304*0.24062
=2.5098
T statistic = [X1 - X2 ]/ S.E
= [51.5-45.2]/2.5098
= 2.5102
The t statistic does lie in the critical region for a one tailed hypothesis test. Therefore, the null hypothesis is rejected. The psychologist hence concludes that couples living above the poverty level have greater relationship satisfaction than couples living below the poverty level.
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