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Bell Curve in MS Excel With Only Three Numbers (25%tile, 50%tile, and 75%tile)

Posted on 2015-01-20
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Last Modified: 2015-01-27
Hi, Can somebody detail how to create Bell Curve charts in MS Excel 2013 when given only three sets of #s - the 25th percentile numbers, the 50th percentile numbers, and the 75 percentile numbers ?   Based on a Z-table of entries the 25th percentile is at -.67 standard deviations and the 75th percentile is at .68 standard deviations from the mean (if I am reading this correctly, I am a bit rusty at this though).  The goal is to create the Bell Curve charts in order to determine what the 90th percentile scores or what any other percentile scores would be when given the 25th, 50th, and 75th percentile scores (that is to say, have the Bell Curve charts complete the scale based on the given 25th, 50th, and 75th percentile inputs).  TIA ...
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Question by:LGroup1
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Expert Comment

by:Flora
ID: 40561409
If you upload a dummy data WB, then I eould create the chart
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Author Comment

by:LGroup1
ID: 40562269
Thanks. This is an example of the data that is available:  25% = 55; 50%      = 61; 75% = 66.    Is there some way to create a bell curve chart and project what the 10th percentile, or 90th percentile, or any other percentile would be based on this limited information (using Excel) ?
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by:jburgaard
jburgaard earned 500 total points
ID: 40563151
You can make a cumulated graph (X Y diagram) by means of the build-in statistical function inverse normal.
This is partly translated:  =norm.inv(P,mean,deviation)

HTH
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by:jburgaard
jburgaard earned 500 total points
ID: 40563167
excel X Y graph from build in function
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jburgaard earned 500 total points
ID: 40567950
If you want to SOLVE the percentile problem mentioned, you should use the mentioned build in (cumulated-)function.
If however you would like to ILLUSTRATE on a Bell-curve perhaps you should look into:
http://exceluser.com/excel_dashboards/normal-curve-new-excel.htm
By the way, if this is a real-life-problem you could run into problem if the underlying distribution is not normal (that is if the 50%-percentil is not exact mid between 25% and 50%)

HTH
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Author Closing Comment

by:LGroup1
ID: 40572630
Cool, thanks all !
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