Stdev

[#1]

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

[hic]

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

[#3]

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

[hic]

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

[hic · Accepted solution]

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;

Load * inline

[Travels, Families

0, 50

1, 80

2, 60

3, 10];

HIC

[#6]

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.

[did]

Dear HIC,

your approach means that stdev operates correctly only with raw data.
In this very case there should be as many rows as count(Families), i.e. = 200.
What about % numbers? What if my table looks like this:
[Travels, Families
0, 25%
1, 40%
2, 30%
3, 5%];
How many rows my raw table must have?

[hic]

If you want one row per family, and there are 200 families, then you can use this script:

Load 

RowNo() as FamilyNo,

* 

Inline

[Travels, Families

0, 25%

1, 40%

2, 30%

3, 5%]

While IterNo() <= 200 * Families;