correlation nabaz n. jabbar near east university 25 oct 2011
TRANSCRIPT
Definition of correlation
• Correlational research determines
to what degree a relationship
exists between 2 variables (or
more variables).
The nature of correlational research• Associational research: When the
relationships among two or more variables are studied without any attempt to influence them. (The same as correlation and causal comparative research).
• Experimental research: Differs from correlational research in that there’s manipulation of variables.
The nature of correlational research
• Correlational research is also
sometimes referred to as a form of
descriptive research because it
describes an existing relationship
between variables.
The nature of correlational research• Positive correlation means that
high scores on one variable (X) tend to be associated with high scores on the other variable (Y).
• Negative Correlation means that high scores on one variable (X) are associated with low scores on the other variable (Y).
Three Sets of Data Showing Different Directions and Degrees of
Correlation
X Y X Y X Y
5 5 5 1 2 1
4 4 4 2 5 4
3 3 3 3 3 3
2 2 2 4 1 5
1 1 1 5 4 2
(A) (B) (C) r = +1.00 r = -1.00 r = 0
Purposes of Correlational Research
• Correlational studies are carried out to explain important human behavior or to predict likely outcomes. (identify relationships among variables).
1. Explanatory studies2. Prediction studies3. More complex correlational techniques
Explanatory studies• To identify relationships among variables.
Prediction studies• If a relationship of sufficient magnitude exists
between two variables, it becomes possible to predict score on one variable when score on related variable is known.
1. Predictor variable: The variable that is used to make the prediction.
2. Criterion variable: The variable about which the prediction is made.
More Complex Correlational Techniques
o Multiple Regressiono Coefficient of multiple correlation(R)o Coefficient of Determinationo Discriminant Function Analysiso Factor Analysiso Path Analysiso Structural Modeling
More Complex Correlational Techniques
• Multiple RegressionTechnique that enables researchers to
determine a correlation between a criterion variable and the best combination of two or more predictor variables.
• Coefficient of multiple correlation(R)Indicates the strength of the correlation
between the combination of the predictor variables and the criterion variable
More Complex Correlational Techniques
• Coefficient of DeterminationIndicates the percentage of the variability
among the criterion scores that can be attributed to differences in the scores on the predictor variable.
• Discriminant Function AnalysisRather than using multiple regression, this
technique is used when the criterion value is categorical.
More Complex Correlational Techniques
• Factor AnalysisAllows the researcher to determine whether many
variables can be described by a few factors.• Path AnalysisUsed to test the likelihood of a causal connection
among three or more variables.• Structural ModelingSophisticated method for exploring and possibly
confirming causation among several variables.
Correlation coefficient
• A decimal number between .00 and +1.00 or –1.00 that indicates the degree to which two quantitative variables are related.
0.00 +1.00-1.00
no relationshipstrong positivestrong negative
Basic Steps in Correlational Research
Problem selection Choosing a sample Selecting or choosing proper instruments Determining design and procedures Collecting and analyzing data Interpreting results
Threats to Internal Validityin Correlational Research
• Subject characteristics• Mortality• Location Instrument decay• Instrumentation Data collector bias• Testing Data collector characteristics
• The following must be controlled to reduce threats to internal validity
Partial Correlation
• A method of controlling the subject characteristics threat in correlational research by statistically holding one or more variables constant.