research methods chapter 12
the correlational research strategy
two or more variables are measured to obtain a set of scores for each individual. examined to identify any patterns of relationship that exist between the variables and to measure the strength of the relationship
scatter plot
a list showing the two scores of each individual or the scores can be shown in a graph
correlation coefficient
numerical value to measure and describe the relationship between two variables
- the direction of the relationship
- the form of the relationship
- the consistency or strength of the relationship
correlation describes 3 characteristics of a relationship:
positive realtionship
there is a tendency for two variables to change in the same direction; as one variable increases, the other also tends to increase
negative relationship
there is a tendency for two variables to change in the opposite direction; increases in one variable tend to be accompanied by decreases in the other
linear relationship
when the data points in the scatter plot tend to cluster around a straight line
Pearson correlation
is used to describe and measure linear relationship when both variables are numerical scores from interval or ratio scales
monotonic relationship
a relationship that is consostently one-directional, either consistently positive or consistently negative
spearman correlation
is used to measure a describe monotonic relationships when both variables are ranks from an ordinal score or have been transformed to ranks
the coefficient of determination
is the squared value of a correlation and measures the percentage of variability on one variable that is determined, or predicted, by its relationship with the other variable
statistical significance of a correlation
is the second important factor for interpreting the strength of a correlation
predictor variable
when a corelational study demonstrates a relationship between two variables, it allows researchers to use knowledge about one variable to help predict or explain the second variable
criterion variable
variable being explained or predicted
- the third-variable problem
- the directionality problem
2 limitations in a Correlational study:
multiple regression
used for studying multivariate relationships