WebDNA Software | Calculating Standard Deviation

Calculating Standard Deviation

I needed to do this for one of my hobby sites, so I thought I would share. Good if you have a scoring or ratings system on your site.

make sure that you have a tab on this line as indicated:
sdev[index]<tab>[math][interpret][dev[index]][/interpret]*[interpret][dev[index]][/interpret][/math]

[!]<!-- The following code will find the standard deviation-->[/!]
[!]<!-- in a range of numbers stored in a database (or table),  -->[/!]
[!]<!-- where math.db is your database of scores                -->[/!]
[!]<!-- 
SAMPLE DATABASE:
rating
8
5
6
5
4
9
7
1
5
6
-->[/!]
[!]<!--Should yield a STANDARD DEVIATION of 2.22-->[/!]

[search db=math.db&neRATINGdatarq=[blank]]
[text show=F]numscores=[numfound][/text]
[founditems]
Rating [index]=[text show=T]num[index]=[rating][/text]<br>
[/founditems]
Total: [text show=T]total=[sum field=rating][/text]<br>
[/search]
Avg: [text show=T]avg=[math][total]/[numscores][/math][/text]<br>
<hr>
[loop start=1&end=[numscores]]
[text show=f]dev[index]=[math]([interpret][num[index]][/Interpret]-[avg])*-1[/math][/text]
[/loop]
[table name=sdev&fields=sku,sdevnum]
[loop start=1&end=[numscores]]
sdev[index]<tab>[math][interpret][dev[index]][/interpret]*[interpret][dev[index]][/interpret][/math]
[/loop]
[/table]
[search table=sdev&neskudatarq=[blank]]
[text show=f]devsum=[sum field=sdevnum][/text]<br>
[/search]

[text show=f]ass=[math][devsum]/([numscores]-1)[/math][/text]
Standard Deviation =[format .2f][math]sqrt([ass])[/math][/format]

Gary Krockover

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Calculating Standard Deviation

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