How do I add a trend line with the 10th, 50th and 90th percentiles to a
scattergram graph?

Excel has no graphics option nor any worksheet function that will do this.

LINEST will give the standard errors of regression coefficients, but not
their covariances (which are needed to get the standard error of a fitted
value). Your options are to either write your own polynomial regression
function, or use a different package. R is a freely available
http://www.r-project.org
full-featured and widely used statistical package that is an open-source
implementation of the S languaguage, that can easily do what you want.

Jerry

"Ruben" wrote:

How do I add a trend line with the 10th, 50th and 90th percentiles to a
scattergram graph?