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
1) Mean
2) Median
3) Mode
Measures of Variability
1) Range
2) Variance
3) Standard Deviation
Variance
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 Product-Moment Correlation
2) Spearman Rank-Difference Correlation
3) Point-Biserial Correlation
4) Biserial Correlation
Pearson Product-Moment Correlation
Both variables continuous and on an Interval or Ratio Scale
Spearman Rank-Difference Correlation:
both variables on an Ordinal Scale
Point-Biserial 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