Chapter 2
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Nominal Scales
Qualitative system for categorizing objects or people i.e Female =1, Male = 2

Ordinal Scales
 Allows you to rank people or objects according to the quantity of a characteristic i.e
 Class Rank

Interval Scales
Allows ranking on a scale with equal units i.e IQs, GRE scores

Ratio Scales
Properties of interval scales with a true zero point ie height in inches, weight in pounds

Distribution
A set of scores

Measures of Central Tendency

Measures of Variability
 1) Range
 2) Variance
 3) Standard Deviation


Variance
Measure of variability in distribution of scores

Standard deviation
Used in interpreting scores: square root of variance

Correlation Coefficient
mathematical measure of the relationship between two variables:
 range 1.0 to + 1.0
 sign indicates the patter of the relationship
 size indicates the strength of the relationship

Scatterplots
graph depicting the relationship between two variables. Each mark in the scatterplot actually represents two scores, an individual's scores on the X and Y variable

Major Types of Correlations(4)
 1) Pearson ProductMoment Correlation
 2) Spearman RankDifference Correlation
 3) PointBiserial Correlation
 4) Biserial Correlation

Pearson ProductMoment Correlation
Both variables continuous and on an Interval or Ratio Scale

Spearman RankDifference Correlation:
both variables on an Ordinal Scale

PointBiserial Correlation
ONe variable continuous and on Interval/Ratio scale, the other a genuine dichotomy

Biserial Correlation
Both variables continuous and on Interval/Ratio scale, but one is reduced o two categories

Factors that effect correlations
 1) If another type of relationship exists, traditional correlations may underestimate the correlation
 2) If there is a restriction of range in either variable, the magnitude of the correlation will be reduced

Qualitative interpretation of correlations
 < .3 Weak
 .3  .7 Moderate
 > .7 Strong

Statistical Significance of Correlations
determined both by the size of the correlation coefficient and the size of the sample

Coefficient of Determiniation(r squared)
The proportion of variance on one variable that is determined or predicatble from the other variable

Coefficient of Nondetermination (1  r squared)
The proportion of variance in one variable that is not determined or predicatable from the other variable

Linear Regression
 A statistical technique for predicting scores on one variable given a score on another
 Predicts criterion scores based on a perfect linear relationship
 Strong correlations result in accurate predictions; weak correlations resul in less accurate predictions