Definition of Trend Line for 2 time series

[mgrehan]

I am graphing 2 time series in a Line Chart.  The Combine Series option automatically is on - if I switch it off the Trend Line doesn't alter which worries me.

I can see from browsing the forums that for 1 time series the Trend Line is Simple Linear Regression but I'd like to know what the definition is for two lines. Is there documentation to define what the Trend Line is in this situation?

[v-huijiey-msft]

Hi @mgrehan ,

Hope everything is going well.

Trend line currently require a continuous axis to be used.

When you plot two time series in a single visual and use the Combined Series option, Power BI treats the data as part of the same context but preserves their different paths.

When the Combined Series option is turned off, the trend line is calculated based on each series' own data points and the linear regression formula.

You do not see the trend line change when you switch the " Combined Series " option. You can lengthen the Y-Axis a little longer, maybe the visual effect is not obvious.

Or you can publish your problem to Home (microsoft.com)  to better help us improve our functions.

I would be grateful if you could provide a little more detail on your sample data instead of screenshots, like what type of data are your Y-axis and X-axis.

Thank you for your patience and cooperation.

Best Regards,
Yang
Community Support Team

If there is any post helps, then please consider Accept it as the solution  to help the other members find it more quickly.
If I misunderstand your needs or you still have problems on it, please feel free to let us know. Thanks a lot!

[mgrehan]

Hi,

Thanks for your response.

The X-Axis is Date. The Y Axis is Sales for that particular date.

I do not understand this sentence " Power BI treats the data as part of the same context but preserves their different paths."

I need a mathematical explanation for the work context or I cannot use the trend line - I know you're trying to be helpful but this statement is too vague for me to be clear on what exactly the calculation of the trend line is. Documentation on the exact calculations is really what I require. Does that exist?

[v-huijiey-msft]

Hi @mgrehan ,

Thank you for your response and patience, it was very helpful in resolving the issue successfully.

"Power BI treats the data as part of the same context but preserves their different paths." which simply means looking at two lines together.

Could you please check that your dates are consecutive, as trend line currently require the use of consecutive axes.

You can pull the height of the visual object up a bit, it may be that the change is not obvious to the naked eye.

I would appreciate if you could provide me with sample data to test.

If you have any other questions please feel free to contact me.

Best Regards,
Yang
Community Support Team

If there is any post helps, then please consider Accept it as the solution  to help the other members find it more quickly.
If I misunderstand your needs or you still have problems on it, please feel free to let us know. Thanks a lot!