# CCJS 300 Chapter Notes - Chapter 13: Phi Coefficient, Nonparametric Statistics, Parametric Statistics

by OC2395438

School

University of MarylandDepartment

Criminology and Criminal JusticeCourse Code

CCJS 300Professor

Alan LehmanChapter

13This

**preview**shows half of the first page. to view the full**2 pages of the document.**-Statistics summarize data

-Two types of statistics:

-Descriptive statistics: summarizes or describes data or shows relationships between variables

-Inferential statistics: enable generalization or interference of sample findings to larger

populations

-Measures of central tendency: summary statistics that describe the typical, middle, or average

score (mode, median, mean)

-Mode: most frequently occurring score, simplest measure of central tendency

-Median: midpoint, most appropriate for ordinal data

-Mean: average score, most familiar measure of central tendency

-Measures of dispersion: spreadoutness of the data

-Range: simplest measure of dispersion, represents the highest and lowest scope or the

difference between them

-Standard deviation: highly useful, plus or minus one standard deviation always equals

68 percent of a normal curve

-Normal distribution: bell-shaped curve that describes a variety of phenomena. For

example, a large sample of a population will be normally distributed and resemble a

normal curve

-Standard deviation units (z score): measure the deviation from the mean relative to the

standard deviation

-Chi-square: a test of the independence of the relationship between nominal-level variables

-Unstable in the 2x2 case

-Harder with a larger number of cells

-Degrees of freedom: the number of cells that are free to vary

-Chi-square based measures of association:

-Phi coefficient and phi-square: a PRE (proportionate reduction in error) measure in

knowledge of one variable enables one to predict the second

-Contingency coefficient: a chi-square-based measure of relationship in which a zero

equals no relationship, but the upper limit is less than one

-Cramer’s V: a useful chi-square-based measure of relationship appropriate for a 2x2

table

NATURE AND TYPES OF STATISTICS

-Parametric statistics: assume some interval level of measurement and a normal population

(better for interval data)

-Nonparametric statistics: distribution free statistics in which few assumptions are made

regarding the normality of the population (better for nominal and ordinal data)

-Null hypothesis: assumes that there is no difference between the groups being compared or no

relationship in the population

-Tests of significance: assesses whether the differences between observed and expected values

could be due to chance (sampling error) or are statistically significant

-Level of statistical significance is set by the researcher in terms of the amount of risk or

willingness to be in error in rejecting the null hypothesis

-T test: used to compare the sample means of two groups, developed for the benefit of

students

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