using spss to compare means udp 520 lab 4 lin november 6 th, 2007
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Using SPSS to Compare Means
UDP 520 Lab 4Lin Lin
November 6th , 2007
Outline
• Dataset
• Independent samples
• Paired samples
Dataset—Weight Lost Training Program (WLTP)
• 1000 adults aged 18+ (including both males and females) were recruited to study the effectiveness of Weight Lost Training Program.
• Variables– Sex– BMI_1(before WLTP)– BMI_2(after WLTP)
• Download dataset fromhttp://courses.washington.edu/urbdp520/UDP520/WLTP_new.sav
2 2
( )BMI=703
( )
Weight lb
height in
Questions
• Question one: – Is BMI significantly different between
males and females before WLTP?
• Question two: – Overall (for both males and females), is
WLTP effective?
Question One
• Step one: Making assumptions and meeting test requirements – Random sampling– Level of measurement is interval-ratio– Sampling distribution is normal
• Step two: stating the null hypothesis
• Step three: 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 :
males females
males females
u u
u u
Question One (cont.) Step four: computing the test statistic in SPSS
Question One (cont.)
• Step five: making a decision and interpreting the results of the test
Independent Samples Test
2.313 .129 -.989 998 .323 -.07871 .07960 -.23492 .07749
-.990 996.636 .323 -.07871 .07953 -.23477 .07735
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
resultor Z (obtained)
Question Two
• Step one: Making assumptions and meeting test requirements – Random sampling– Level of measurement is interval-ratio– Sampling distribution is normal
• Step two: stating the null hypothesis
• Step three: 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 :
before after
before after
u u
u u
Question Two (cont.) Step four: computing the test statistic in SPSS
Question Two (cont.)
• Step five: making a decision and interpreting the results of the test
Paired Samples Correlations
1000 .657 .000BMI_1 & BMI_2Pair 1N Correlation Sig.
Paired Samples Test
.42943 1.47901 .04677 .33765 .52121 9.182 999 .000BMI_1 - BMI_2Pair 1Mean Std. Deviation
Std. ErrorMean Lower Upper
95% ConfidenceInterval of the
Difference
Paired Differences
t df Sig. (2-tailed)
resultor Z (obtained)
Exercises
• Is BMI significantly different between males and females after WLTP?
• Is WLTP effective for males? – Hint (do selection in “Data”— “Select
cases”— “if condition is satisfied”— “if”— “sex=0”)
• Is WLTP effective for females?
Selecting cases in SPSS