How to solve the problem of a new aggregation based on the other aggregation

tableaucommunity@tableau.com — Sat, 17 May 2014 13:19:28 GMT

Hi folks,

I have a problem. First, I have a calculated field named "Average gain" which is "AVG([Posttest answer])-AVG([Pretest answer])". Then I want to know the standard deviation of this "Average gain", but "STDEV([Average gain] )" is wrong as Tableau complains "STDEV (an aggregate function) is already an aggregation, and cannot be further aggregated." How can I solve this problem? I need this SD!!!

Qin

HELP: A heat map I want

tableaucommunity@tableau.com — Sun, 02 Mar 2014 22:05:03 GMT

A sample data spreadsheet is attached to this topic. As you can see their are 10 students with the pre&post survey results, what I want is a heat map which shows the total of student in different response cases, like this:

all right (1,1) | right to wrong (1,0)

------------------------------------------------------

wrong to right (0,1) | all wrong (0,0)

"all right" means the student gets the right answer both in pre&post test. If the size of this part is percentage in the heat map , it should be "all right number / right number in pretest". From this plot, I can easily find whether our project helped students.

So how can I make it?

Thanks those who think about and answer my question in advance.

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How to solve the problem of a new aggregation based on the other aggregation

HELP: A heat map I want