It is called a when members of the population volunteer to take part in the sample.

random sample
self-selected sample
biased sample
convenience sample

Match the item to the definition: indirect correlation, correlational research, correlational research, covary, pearson correlation coefficient, pearson correlation coefficient, direct correlation a. used to describe the relationship between two or more naturally occurring variables b. determines whether scores on the two variables covary c. whether two variables vary or change together d. denoted by the symbol "r" e. provides information about the sign (direction) and magnitude(strength) of the linear relationship. f. when the correlation is positiveg. when the correlation is negative