R-squared value meaning

[niravrph]

Hi,

I have a bunch of charts with 6 months of data in each (JAN - JUN). Some of the charts show R-squared values for my trendlines with a value nearing 1.0. That's great. However some have very low values on the order of 0.2 or 0.3.

I'm not good at math but shouldn't they all have high values if they all have 6 months of data each? How can one chart have a highly reliable trendline but others don't? What does it mean/how does this work?

Thanks,
NIRAV

 

[VoG]

R-squared is a measure of the goodness of fit of the trendline to the data. A value of 1 is a perfect fit. See http://en.wikipedia.org/wiki/Coefficient_of_determination