Textbook Notes (280,000)
US (110,000)
UMD (1,000)
CCJS (70)
Chapter 13

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

Department
Criminology and Criminal Justice
Course Code
CCJS 300
Professor
Alan Lehman
Chapter
13

This 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