6 Replies Latest reply: Sep 6, 2016 3:59 PM by Clever Anjos

# linest_m trendline correct value?

Hi!

I have a chart (below) that shows Revenue over recent Weeks... In my chart I have added the trendline.

I want to use the calculate the slope and found the linest_m function, my expression is like this: LINEST_M(Revenue, Week)

But the result of my expression showed: -738,47539

Shouldn't the result be a positive value, as the trend is positive? What am I doing wrong?

Best regards,

Filip

• ###### Re: linest_m trendline correct value?

Yes, you would probably expect a positive value. But it's hard to say what's causing the difference just by looking at the image.

Could you post a small sample app (or the data you are using as Excel or INLINE LOAD table)?

• ###### Re: linest_m trendline correct value?

This is other numbers, but still the value gets wrong when counting on a conditional trendline... Please see my attached example.

Best,

Filip

• ###### Re: linest_m trendline correct value?

Filip,

the value that linest_m returns seems correct to me (you can check this by calculating the slope with Excel, for example).

I think the equation that the linear regression option in chart properties will show is terribly wrong. It seems to me that QV is not taking the different x-step sizes correctly into account when calculating the lienar regression. In fact, if you change the axis to continuous in axes tab,the x-step sizes are shown correct, and the produced linear regression, too.

(Tested in QV 11.20.11643.0 IR)

IMO, you can and should report this as bug to QT support.

Regards,

Stefan

• ###### Re: linest_m trendline correct value?

OK, I can agree that QV may not calculate properly when there are differences on the x axis.

Please take a look at my attached qv-document. I still can't understand if I am doing something wrong when fetching the Trend Value.

What I want to do is visualize the trend with a text 'Positive'/'Negative'... But I can't find my simple calculations reliable as the value even gets negative with a clear positive trend in the chart.

Best regards,

Filip

• ###### Re: linest_m trendline correct value?

Filip,

one big difference between your charts and the linest_m expression is the fact that you aggregate your revenue values in the line chart, but not in the linest_m function (and since your data shows multiple records per week, even for the same flag, that's a big difference).

You can modify your linest_m function to:

=LINEST_M(aggr(sum(Revenue), Week),aggr(Week,Week))

to produce the same result as your chart (considering the additional bug with non continuous x-axis values as discussed before).

Regards,

Stefan

• ###### Re: linest_m trendline correct value?

I´ve just noticed similar behaviour here.

The "show equation" of feature trendline seems to be buggy

I´ve created a very, very example.

LINEST_M seems to be ok with the plotted equation

LINEST_B is totally different.

I´ve included an expression into the line graph with linest_m and linest_b and the lines are ok (my line and trendline) but the  "b" value for the equation is not ok