How to Find the Correlation Coefficient on a TI-84

The correlation coefficient, r, measures how tightly two variables move together in a straight-line relationship. It always falls between -1 and 1: values near 1 mean a strong positive relationship (as one variable goes up, so does the other), values near -1 mean a strong negative one, and values near 0 mean little to no linear relationship at all.

Where it comes from

r isn’t computed on its own — it comes out as a byproduct of running a linear regression on paired (x, y) data. On a TI-84, that’s STAT → CALC → LinReg(ax+b), which reports the slope, intercept, r, and r² all at once (diagnostics need to be turned on in MODE for r to display).

r² (the coefficient of determination) is r squared, and tells you what fraction of the variation in y is explained by the linear relationship with x — an r of 0.9 means r² = 0.81, or 81% of the variation explained.

Reading the sign

The sign of r always matches the sign of the regression slope: a positive slope means positive correlation, a negative slope means negative correlation. If your regression line trends downward, r will be negative even if r² alone wouldn’t tell you that.

Try it yourself

In Tools → Lists & Stats on the TI-84 Calculator, enter your paired data into two lists, select them as X and Y, choose Linear from the regression menu, and press Regress — the result includes r², and r is its square root with the sign of the slope. For a significance test on the relationship (not just its strength), Tools → Tests → LinRegTTest runs the hypothesis test that the slope — and therefore the correlation — is genuinely nonzero.