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# The Excel STEYX Function

Standard Error

In Excel Steyx function calculates the standard error for the straight line of best fit through a supplied set of x- and y- values. This line satisfies the simple straight line equation:

**y = mx + b**

where,

- x is the independent variable;
- y is the dependent variable;
- m is the slope (gradient) of the line;
- b is a constant which is the value of y when x = 0.

The standard error for this line provides a measure of the error in the prediction of y for an individual x.

Further information on the standard error can be found on the Wikipedia Standard Error page

## Basic Description

The Excel STEYX function calculates the standard error for the line of best fit, through a supplied set of x- and y- values.

The format of the function is:

STEYX( known_y's, known_x's )

Where the function arguments are:

known_y's | - | An array of known y-values (the dependent variables). |

known_x's | - | An array of known x-values (the independent variables). (This must contain the same number of data values as the known_y's array). |

Note that the Steyx function will interpret text representations of numbers as numeric values. Other text values, that cannot be interpreted as numbers are ignored, along with the corresponding value in the other array of x- or y- values.

## Steyx Function Example

Cells A2 - A10 and B2 - B10 of the above spreadsheet on the right contain a set of known x- and known y- values.

The spreadsheet also shows these points, plotted on a chart, along with the line of best fit through the points.

The Standard Error for the line of best fit can be calculated by the Excel Steyx function. This function, as shown in cell C12 of the example spreadsheet, has the form:

=STEYX( B2:B10, A2:A10 )

and returns the value *1.201186347*.

Further information and examples of the Excel Steyx function are provided on the Microsoft Office website.

## Steyx Function Errors

If you get an error from the Excel Steyx function this is likely to be one of the following:

Common Errors

#N/A | - | Occurs if the array of known_x's is not the same length as the array of known_y's. |

#DIV/0! | - | Occurs if the supplied known_x's and known_y's arrays contain fewer than 3 values. |