5 Replies Latest reply: Jan 5, 2013 4:43 PM by Zach Alexy

# Stdev

Hi,

Can anybody help me with the Stdev function. I can't get it to work.

Simple case with question asked how many travels (0, 1, 2 or 3) a year a family undertakes. 200 families answered:

Travels, Families

0, 50

1, 80

2, 60

3, 10

Stdev(Aggr(Sum(Travels), Families)) gives me 1.29. It should be approx. 0.85.

Any help?, Zach

• ###### Re: Stdev

But why do you use the Aggr function? This creates a nested aggregation and you need only a single aggregation. The expression "stdev(Travels)" will give 0.85 as answer.

HIC

• ###### Re: Stdev

Hi, thanks for your reply. If I use stdev(Travels) i still get the 1.29?

• ###### Re: Stdev

If you have the raw data, i.e all 200 records, then stdev will work the way you expect it. But if you calculate it from a table of just four records (the ones in your initial post), then 1.29 is correct.

You can most likely calculate it indirectly from you four records using a formula with weighted values (you need to weight the "travels" number by number of families).

HIC

• ###### Re: Stdev

If you load the data using the following script, you will recreate the raw data and the stdev (and average and all other statistical entities) will be calculated correctly:

Data:

Load * while iterno()<= Families;

[Travels, Families

0, 50

1, 80

2, 60

3, 10];

HIC

• ###### Re: Stdev

Hi Henric,

Very helpfull. I thought that the Stdev function would 'automatically' expand over the two elements. Good to know that I need all the individual records for Stdev to work the way I want it to. I now understand that the 1.29 simply is the standard deviation of 0, 1, 2 and 3 occuring 1 time each.

Thank you.