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Nominal Scales
Qualitative system for categorizing objects or people i.e Female =1, Male = 2
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Ordinal Scales
- Allows you to rank people or objects according to the quantity of a characteristic i.e
- Class Rank
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Interval Scales
Allows ranking on a scale with equal units i.e IQs, GRE scores
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Ratio Scales
Properties of interval scales with a true zero point ie height in inches, weight in pounds
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Distribution
A set of scores
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Measures of Central Tendency
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Measures of Variability
- 1) Range
- 2) Variance
- 3) Standard Deviation
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Variance
Measure of variability in distribution of scores
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Standard deviation
Used in interpreting scores: square root of variance
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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
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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
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Major Types of Correlations(4)
- 1) Pearson Product-Moment Correlation
- 2) Spearman Rank-Difference Correlation
- 3) Point-Biserial Correlation
- 4) Biserial Correlation
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Pearson Product-Moment Correlation
Both variables continuous and on an Interval or Ratio Scale
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Spearman Rank-Difference Correlation:
both variables on an Ordinal Scale
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Point-Biserial Correlation
ONe variable continuous and on Interval/Ratio scale, the other a genuine dichotomy
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Biserial Correlation
Both variables continuous and on Interval/Ratio scale, but one is reduced o two categories
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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
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Qualitative interpretation of correlations
- < .3 Weak
- .3 - .7 Moderate
- > .7 Strong
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Statistical Significance of Correlations
determined both by the size of the correlation coefficient and the size of the sample
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Coefficient of Determiniation(r squared)
The proportion of variance on one variable that is determined or predicatble from the other variable
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Coefficient of Nondetermination (1 - r squared)
The proportion of variance in one variable that is not determined or predicatable from the other variable
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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
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