Discrepancy between data analysis regression equation and linear trendline equation

[Marinegirl]

Hiya

The equation and R2 value produced by doing a linear regression in the data analysis add on pack are different to the equation and R2 value produced by adding a linear trendline to a scatterplot of the same data. I can change it on the chart using More trendline options, set intercept, but I wondered why the equations are different (and which one is right!)?

Many thanks

[Marinegirl]

aaahh I've solved this one. It was probably just me being daft. The last data point in the seriese on the y axis was missing off the scatter plot chart. However, a lot of students got exactly the same wrong chart / equation, so I wonder if there may be a problem with Excel not picking up all of the data all of the time, rather than mass clumsiness?

[shg]

If you're talking about the R2 value for a regression with a constrained intercept, see http://www.curvefit.com/linear_regression.htm

[Marinegirl]

Cheers shg!

It turned out to just be some sort off data inputting problem - probably user error - but that site has a lot of nice information thank you x