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Chapter 9 - Descriptive Statistics
Chapter 9 IACA
33
Criminal Justice
Professional
09/05/2014

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Term
Statistics
Definition
science of collection and organizing data to then draw conclusions based on data
Term
Types of stats
Definition
descriptive, multivariate, inferential
Term
Descriptive statistics
Definition
summary of large data sets to be put into an easy to read manner
Term
Multivariate
Definition
allows comparisons of factors by isolating the effect of one variable from others
Term
Inferential
Definition
statements of a population based on a sample
Term
Levels of measurement
Definition
nominal, ordinal, interval and ratio
Term
Characteristics of nominal data
Definition
lowest level, must be exhaustive, mutually exclusive, only classified one way, provides names or labels (race, gender), can only be one of something
Term
Characteristics of ordinal data
Definition
exhaustive, mutually exclusive, exhibits a degree of difference, the degree of difference indicates order/rank, ordering distance has no meaning (good, better, best/agree, disagree, neutral)
Term
Characteristics of interval
Definition
assumes all items on scale have equal units of measurement, distance between categories have meaning, logical distances (temp readings, IQ score)
Term
Characteristics of Ratio
Definition
has all the characteristics of the other levels plus a true "zero" point. highest level of measurement. (income, weight, time, age)
Term
Frequency distribution
Definition
lists the number or frequency of scores/labels for each case
Term
Range
Definition
summary statistic with limited information. Highest score-lowest score= range
Term
Class interval
Definition
i= range/"n" of desired intervals

example:i=12-1/4=11
11/4= 2.75
i=2.75
Term
Mean
Definition
average
Term
Median
Definition
midpoint/middle score
Term
Mode
Definition
most frequent score/label
Term
Variance
Definition
sum squared (S^2)deviations of each score from the mean divided by the total number
Term
Standard deviation
Definition
average distance each data item is away from the mean of the all the data items. Provides comparison insight between two distributions.
Term
Skewness
Definition
the spread of scores weighted to one side of the mean.
Term
Normal skewness
Definition
bell shape, the curve doesn't touch the x-axis, curve is symmetrical. Mean, median, mode are equal.
Term
Positive skewness
Definition
unimodial scores weighted to the left. Hump to the left, tail to the right. Mode is the largest, followed by the median, and then mean.
Term
Negative skewness
Definition
unimodial weighted to the right (hump to the right, tail to the left). Mean largest value, then median, then mode.
Term
Rates
Definition
used to standardize measure for comparison between two different items of size. (compare car theft rates between two cities with significant difference in population size).
Term
Proportions
Definition
example:

60 officers / 15 sgts

(15/75)= .20 portion of sgts
(60/75) = .80 portion of officers
Term
Percent changes
Definition
subtract old value from new value then divide by old value then multiply by 100.
Term
Correlation analysis
Definition
measures the relative fit or degree of association between two variable or 3 or more variables to determine the quality of regression line or reliability of prediction.
Term
Pearson's product moment coefficient
Definition
=r
operates within range 1.0, the closer to one the stronger the value. Zero = no correlation.
Term
Regression analysis
Definition
seeks general pattern evident in observation relationships through pattern recognition and placement on a trendline.
Term
Regression analysis and correlation analysis are similar except regression
Definition
locates the best line through the points.
Term
Linear function
Definition
is one in which data points, x & y coordinates, make more a less straight line.
Term
Non-linear function
Definition
is one which the data points, x & y data, make some type of curve shape that can be expressed by an algebraic formula.
Term
Linear regression
Definition
to find the best straight line through the points and has the smallest variance, reflecting gaps between the actual placement of the data points on the graph.
Term
Statistical analysis
Definition
is multivariate in nature when two or more variables (usually of ratio or interval type) are examined together with the focus on observable relationships or patterns of association, between or among the variables.
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