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Using SPSS for Chi Square
UDP 520 Lab 5Lin Lin
November 8th, 2007
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Outline
• Dataset
• Review t-test
• Chi-square
• Exercise
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BMI
• Body mass index (BMI) is a measure of body fat based on height and weight that applies to both adult men and women.
– Under & normal weight: BMI <25 – Overweight & obesity: BMI ≥ 25
2 2
( )BMI=703
( )
Weight lb
height in
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Dataset – WLTP
• 1000 adults aged 18+ (males and females) were recruited to study the effectiveness of Weight Loss Training Program (WLTP)
• Variables– Sex (female=1)– BMI_1(before WLTP)– BMI_2(after WLTP)– Urban or suburban (urban=1)– Overweight_1 (overweight before WLTP) (overweight=1)– Overweight_2 (overweight after WLTP) (overweight=1)
http://courses.washington.edu/urbdp520/UDP520/WLTP.sav
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Question 1
• Is BMI significantly different between people who live in an urban area and those who live in a suburb area before WLTP?
Independent samples t-test
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Question 1 – Step by Step
• Step 1: Making assumptions and meeting test requirements – Sampling is random– Level of measurement is interval-ratio– Sampling distribution is normal
• Step 2: Stating the null hypothesis
• Step 3: Selecting the sampling distribution and establishing the critical region – Sampling distribution = Z distribution – Alpha = 0.05, two-tailed– Z(critical) = ±1.96
0
a
H :
H :urban suburban
urban suburban
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Question 1 (cont.) Step 4: Computing the test statistic in SPSS
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Question 1 (cont.)
• Step 5: Making a decision and interpreting the results of the test
Independent Samples Test
12.928 .000 6.306 998 .000 .49266 .07813 .33934 .64598
6.276 955.970 .000 .49266 .07850 .33861 .64670
Equal variancesassumed
Equal variancesnot assumed
BMI_1F Sig.
Levene's Test forEquality of Variances
t df Sig. (2-tailed)Mean
DifferenceStd. ErrorDifference Lower Upper
95% ConfidenceInterval of the
Difference
t-test for Equality of Means
Result(Z obtained)
Indicate whether result is significant or not
(based on your predetermined alpha)
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Question 2
• Is there any relationship between living in a suburban area and being overweight before WLTP? – Under & normal weight: BMI <25 – Overweight & obese: BMI ≥ 25
Chi Square test
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Question 2 – Step by Step
• Step 1: Making assumptions and meeting test requirements – Random sampling– Level of measurement is nominal
• Step 2: Stating the null hypothesis – H0: Living in an urban area and being overweight are
independent– Ha: Living in an urban area and being overweight are dependent
• Step 3: Selecting the sampling distribution and establishing the critical region – Sampling distribution = χ2 distribution – Alpha = 0.05– Df = (r-1)(c-1) = 1 (a 2-by-2 table)– χ2 (critical) = 3.481
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Question 2 (cont.) Step 4: computing the test statistic in SPSS
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Question 2 (cont.)
• Step 5: making a decision and interpreting the results of the test
overweight_1 * urban Crosstabulation
329 468 797
385.7 411.3 797.0
155 48 203
98.3 104.7 203.0
484 516 1000
484.0 516.0 1000.0
Count
Expected Count
Count
Expected Count
Count
Expected Count
0
1
overweight_1
Total
0 1
urban
Total
Chi-Square Tests
79.699b 1 .000
78.301 1 .000
82.696 1 .000
.000 .000
79.619 1 .000
1000
Pearson Chi-Square
Continuity Correctiona
Likelihood Ratio
Fisher's Exact Test
Linear-by-LinearAssociation
N of Valid Cases
Value dfAsymp. Sig.
(2-sided)Exact Sig.(2-sided)
Exact Sig.(1-sided)
Computed only for a 2x2 tablea.
0 cells (.0%) have expected count less than 5. The minimum expected count is 98.25.
b.
Result(χ2 obtained)
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Question 2 (cont.)
Symmetric Measures
.272 .000
1000
Contingency CoefficientNominal by Nominal
N of Valid Cases
Value Approx. Sig.
Not assuming the null hypothesis.a.
Using the asymptotic standard error assuming the null hypothesis.b.
The nominal symmetric measures indicate both the strength and significance of the relationship between the row and column variables of a crosstabulation.
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Exercise
• Does a significant relationship exist between living in a suburban area and being overweight after WLTP?
• Does a significant relationship exist between being a male and overweight before WLTP?
• Does a significant relationship exist between being a male and overweight after WLTP?