Correlational Study

Types of Correlation Procedures

The Pearson product-moment coefficient is the most commonly used correlational procedure. This procedure is only appropriate, however, for continuous variables that can be measured on an interval or ratio scale; that is, numerical variables that have equidistant points such as weight in kilograms, IQ scores, and number of minutes spent practicing. For ordinal scale variables that are measured in terms of ranks and do not have equidistant points, such as chair placement in a band audition (because the difference in the performance standard between, say, the first and second chair is not necessarily the same as that between the second and third chair), the Spearman's rho or Kendall's tau would commonly be used. The point biserial can be used when researchers correlate two variables whereby one variable comprises continuous data and the other dichotomous data (i.e., 0s and 1s), while the phi correlation may be used if both variables are dichotomous.

Correlation Coefficient

Correlation strength is measured by the “correlation coefficient.” When using the Pearson product-moment coefficient, this correlation coefficient is represented as the “r value.” This value ranges from −1.00 (perfect negative correlation) to +1.00 (perfect positive correlation). An r value that is close to either end implies a strong relationship and may be described as high, an r value that tends toward zero suggests a weak relationship and may be termed as low, and an r value that lies between high and low values can be called moderate. It is crucial to note that a curvilinear (i.e., nonlinear) relationship cannot be detected through the r value; hence, it is important during statistical analysis to examine scatter plots. These are graphs consisting of plotted points that enable one to visually ascertain if there are linear relationships between two variables through an examination of the “line of best fit” (i.e., a line drawn that is as close as possible to as many points as possible).

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