WK 5 - Jackson Ch. 6 Notes.docx - 510 – Wk 5- Jackson Notes...

510 – Wk 5- Jackson Notes – Chapter 6
Conducting Correlation Research 6.1
Correlation coefficients tell us about only linear relationships
Correlational designs allow you to describe the relationship between two measured variables.
A correlation coefficient (descriptive statistic) helps by assigning a numerical value to the observed relationship.
When conducting correlational studies, researchers determine whether two variables (for example, height and
weight or smoking and cancer) are related to each other.
Such studies assess whether the variables are “correlated” in some way
The correlational method is a type of nonexperimental method that describes the relationship between two
measured variables.
In addition to describing a relationship, correlations allow us to make predictions from one variable to another.
Magnitude An indication of the strength of the relationship between two variables.
o Correlations vary in their magnitude—the strength of the relationship.
o Sometimes there is no relationship between variables, or the relationship may be weak; other
relationships are moderate or strong.
o Correlations can also be represented graphically in a scatterplot or scattergram.
o In addition, relationships are of different types—positive, negative, none, or curvilinear.
o A correlation coefficient is a measure of the degree of relationship between two variables; it can
vary between -1.00 and +1.00.
o The stronger the relationship between the variables, the closer the coefficient is to either -1.00
or +1.00.
o The weaker the relationship between the variables, the closer the coefficient is to 0.
o We typically discuss correlation coefficients as assessing a strong, moderate, or weak
relationship, or no relationship.
A correlation coefficient of +/-1.00 represents a perfect relationship, a coefficient of 0.00 indicates no
relationship between the variables.
Scatterplots
Scatterplot A figure that graphically represents the relationship between two variables.
o A scatterplot or scattergram, a figure showing the relationship between two variables,
graphically represents a correlation coefficient.
o In a scatterplot, two measurements are represented for each participant by the placement of a
marker.

510 – Wk 5- Jackson Notes – Chapter 6
o The stronger the correlation, the more tightly the data points cluster around an imaginary line
through their center.
o When there is a perfect correlation (+/-1.00), the data points all fall on a straight line.
o In general, a scatterplot may show four basic patterns:
 a positive relationship
 a negative relationship
 no relationship, or
 a curvilinear relationship.
Positive Relationships – Positive relationship between two variables. Fig.6.2(a)
- A positive correlation , one in which a direct relationship exists between the two variables.
- This means that an increase in one variable is related to an increase in the other, and a decrease in one is
related to a decrease in the other.