ps 225 lecture 17 comparing two variables. in-class analysis
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PS 225Lecture 17
Comparing Two Variables
In-Class Analysis
Independence vs. Dependence
Independence: Variables are not related Dependence: Variables demonstrate
correlation Independent Variable Dependent Variable
Chi-Squared Statistic
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eo
f
ff 22 )(
Hypothesis Test for Independence
Ho: Variables are Independent
H1: Variables are Dependent
SPSS Chi-Square Test
Hypothesis Test for Independence Result
Reject Ho and conclude H1 : Variables are dependent
Don’t Reject Ho : Not enough information to conclude variables are dependent
Chi-Squared Test
Test for independence Can be used for nominal and ordinal
data Nonparametric test
Conditional Distribution
Extreme Conditional Distributions
No Association Perfect Association
Measures for Nominal Variables
Phi (Φ) for 2x2 tablesCramer’s V for larger tables
Phi (Φ)
N
2
Phi (Φ)
Between 0 and 1 0 No Correlation 1 Perfect Correlation
Guidelines for Interpreting Phi
Less than 0.10 : Weak Between 0.10 to 0.30 : Moderate Greater than 0.30 : Strong
Cramer’s V
)1,1)(min(
2
crNV
Cramer’s V
Between 0 and 1 0 No Correlation 1 Perfect Correlation
Guidelines for Cramer’s V
Less than 0.10 : Weak Between 0.10 to 0.30 : Moderate Greater than 0.30 : Strong
Measures for Nominal Variables Phi (Φ) for 2x2 tables Cramer’s V for larger tables
Measures for Ordinal Variables
Gamma- for collapsed ordinal variables Spearman’s Rho – for continuous ordinal
variables
Gamma
Increase in accuracy of prediction 0-0.3 weak 0.31 to 0.6 moderate Greater than 0.61 strong Sign indicates strength
Spearman’s Rho
Proportionate Reduction in Error (PRE)
Robert Putnam
Political Scientist at Harvard University
Studies Social Capital, “features of social life- networks, norms and trust- that enable participants to act together effectively to pursue shared objectives”
Reading for Next Class
Get Article from JSTOR
Tuning In, Tuning Out: The Strange Disappearance of Social Capital in America
Robert D. Putnam PS: Political Science and Politics, Vol.
28, No. 4. (Dec., 1995), pp. 664-683.
SPSS Assignment What characteristics of individuals might
increase or decrease the likelihood they will engage in activities that build social capital like visiting neighbors (socommun2) or friends (socfrend2)?
Choose three survey responses to study Conduct a Chi-Squared hypothesis test for
independence Give your hypotheses, test results and
interpretation Characterize the relationship using a measure
of association Clearly indicate which measure you use and
give the relative size of the impact of the independent variable.