Looks like a bug to me.
I agree with Alex...and can you post a followup once you hear back from tech support?
It does sound that way. I've sent an email to support...we'll see what they say.
Not convinced this is a bug... more likely something to do with the way the table calc is being done. What is your formula for Forecast Accuracy (not the window_avg forecast accuracy)?
Look at the line chart, the line is all jagged like it's been overwritten many times for each SKU... although I would expect to see multiple segments in the barchart for each SKU..... unless you've got stacked bars turned off?
The formula for Accuracy is:
Literally all I did was change the Mark Type from Bar to Line...nothing else on the chart changed.
But he has the partitioning set explicitly, rather than just table down. I wouldn't expect a difference.
I can replicate this in superstore sales and I can see what's going on...
Turn stack marks off, add category to rows, customer to LoD and a window_avg(sum(sales)) to columns. Set compute using customer and add a average reference line in. Switch between line and bars and the average will change between 7058 and 6957
When its on bars, Tableau is calculating the sum of sales divided by the sum of the dcount of customers in each category - i.e. 14.9M / (657+783+704) = 6957
When on line, it is calculating the average of the average of sales in each category i.e.
Furniture 5.1M / 657 = 7882
Office 3.7M / 783 = 4793
Technology 6M / 704 = 8500
...Average of 7882, 4793, 8500 = 7058
So what's going on... bars are calculating an overall average per customer and line is calculating the average of the average per customer in each category.
Bug or by design...not sure!!
Nice analysis Robin.
That certainly is interesting...maybe it'd by design, but if so, it'd be nice to be able to determine which average is used vs. being locked into only one.
I've sent my workbook to Tableau Support, so maybe a definitive answer will emerge soon.
Have a good weekend.
I thought I'd have a go at it this weekend and I think you've nailed it, thanks for researching this, Robin! The one other bit is that turning Stack Marks Off isn't even necessary to demonstrate this behavior - the reference line goes to 5,611,462 for the line and 4,971,867 for the bars.
From a selfish user standpoint, I'd still call this a bug, I like my results to not change based no the mark type.
No problem... thanks! Sorry it doesn't help the OP, though!
I too will be interested to hear what the Tableau support jedis have to say about this
A little more info on this: The line, area, and filled map all return the same results, while everything else returns the bar, shape, square, circle, text, gantt bar, and pie marks return the different results.
Intuitively, I feel it shouldn't change...