A positive correlation is an association between two variables such that participants with high scores on one variable tend to have high scores on the other variable as well, and those with low scores on one variable tend to have low scores on the other variable.

A correlation coefficient is a statistic that quantifies a relation between two variables.

Psychometricians are the statisticians and psychologists who develop tests and measures.

Test-retest reliability refers to whether the scale being used provides consistent information every time the test is taken.

The Pearson correlation coefficient is a statistic that quantifies a linear relation between two scale variables.

Coefficient alpha, symbolized as α, is a commonly used estimate of a test or measure's reliability and is calculated by taking the average of all possible split-half correlations; sometimes called Cronbach's alpha.

A negative correlation is an association between two variables in which participants with high scores on one variable tend to have low scores on the other variable.

Psychometrics is the branch of statistics used in the development of tests and measures.