Case 1: The x-value and y-value ranges overlap
If the x-value and y-value ranges overlap, the LINEST worksheet function produces incorrect values in all result cells. Normal statistical probability disallows the values in the x and y ranges to overlap (duplicate each other). Do not overlap the x- and y-value ranges when referencing cells in the formula.
Note The Regression tool alerts you to this problem and does not continue. You can use the Regression tool instead of the LINEST worksheet function.
In Microsoft Office Excel 2007, you can find the Regression tool by clicking Data Analysis in the Analysis group on the Data tab.
In Microsoft Office Excel 2003 and in earlier versions of Excel, you can find the Regression tool by clicking Data Analysis on the Tools menu. Case 2: The number of rows is less than the number of x-columns
It is not statistically valid for the number of rows to be less than the number of x (variable) columns. The number of rows of data must be larger than the number of columns of data (x-columns plus y-columns).
Case 3: You specify a zero constant
Do not specify a zero constant (b=0) in the function.