The Excel STEYX function returns the standard error of the predicted y-value for each x in a linear regression — a measure of how far the data points typically fall from the best-fit line.
Syntax
| Argument | Description | |
|---|---|---|
known_ys | Required | The array or range of dependent (y) values. |
known_xs | Required | The array or range of independent (x) values. Must contain the same number of points as known_ys. |
How to use it
STEYX fits a straight line to your x/y data (the same line SLOPE and INTERCEPT describe) and reports the typical vertical distance between the actual points and that line. A small standard error means the points hug the line; a large one means the fit is loose.
Mathematically it is the square root of the residual sum of squares divided by n−2 — the two degrees of freedom lost to estimating the slope and intercept. Because of that n−2, STEYX needs at least three data points.
Pair it with RSQ: RSQ tells you what fraction of variation the line explains, while STEYX tells you the typical error in the same units as your y-values. Together they give a fuller picture of fit quality.
Try it: interactive demo
Pick a STEYX example to see the formula and its result.
Practice workbook
Frequently asked questions
What does STEYX actually measure?
Why does STEYX divide by n minus 2?
n−2 gives an unbiased estimate of the error variance.How is STEYX different from RSQ?
How many data points does STEYX need?
n−2 denominator. With only two points the line fits perfectly and the standard error is undefined.Master functions like this in one day
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