Want to win a PS4? Go Premium and enter to win our High-Tech Treats giveaway. Enter to Win

x
?
Solved

Mean, StdDev, and Variance (for subset of data)

Posted on 2013-06-18
7
Medium Priority
?
515 Views
Last Modified: 2013-06-19
I need some help with computing (in Excel) the mean, standard deviation, and variance.

Trick is that some survey answers have not been selected (e.g., value of 0) and thus must be skipped.

For example, the following data set must provide the following answers:
Answer ID:      Number of Responses
1                       0
2                       0
3                       1
4                       3
5                       0
6                       0
7                       1

Average = 4.40
StDev = 1.52
Variance = 2.30

Again, given that zeros must be ignored, what are the proper Excel functions for each of these three statistics?

Thanks,
EEH
0
Comment
Question by:ExpExchHelp
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
  • 3
7 Comments
 
LVL 24

Accepted Solution

by:
Steve earned 2000 total points
ID: 39257620
It has been a little while since I did StdDev and Variance of Frequency distributions.
But the attached has an attempt by me, but the values are not exactly the same as yours.
I think they are pretty close to the required calculations though.
Formulas.xlsx
0
 

Author Comment

by:ExpExchHelp
ID: 39258965
The_Barman:

Thousand thanks... as I only need two decimals, your numbers match a 100%.

Again, thank you so much for your assistance.

EEH
0
 

Author Comment

by:ExpExchHelp
ID: 39258990
The_Barman:

Again, thanks for your help... quick follow-up.

When I used a few other frequency distribution, their StDev and Variance did not match though.

Example #1:

Score      Frequency
1      1
2      0
3      0
4      1
5      0
6      1
7      0

The survey's tool value equal:  
Mean                        3.67
Standard Dev.      2.52
Variance                        6.33

The Excel formula's (your XLS) result in:
Average      3.67
StdDev      0.86
Variance      0.74

*****************************

Example #2:

Score      Frequency
1      0
2      2
3      2
4      0
5      1
6      0
7      0

The survey's tool value equal:  
Mean                        3.00
Standard Dev.      1.22
Variance                        1.50

The Excel formula's (your XLS) result in:
Average      3.00
StdDev      1.63
Variance      2.67


So, for some strange reason, the original dataset I provided resulted in the same values.   The next two or three frequency distribution, however, resulted in different values.

Any ideas what might be causing this?

Thanks,
EEH
0
Concerto's Cloud Advisory Services

Want to avoid the missteps to gaining all the benefits of the cloud? Learn more about the different assessment options from our Cloud Advisory team.

 
LVL 24

Expert Comment

by:Steve
ID: 39259144
There will likely be something in the order of the formula (braket in wrong place etc)
I will read my book again and should be able to sort it :)
0
 

Author Comment

by:ExpExchHelp
ID: 39259213
The_Barman:

Thanks so much... I truly appreciate it!!

EEH
0
 
LVL 24

Expert Comment

by:Steve
ID: 39259974
OK, I have taken the time to actually make 100% on this one...

The actual values your servey tool is giving for Variance and Standard deviation are for an n-1 standard deviation of a sample rather than population.

In Excel there are two functions Stdev.P and Stdev.S
One uses N as the divisor one uses N-1 as a better approximation of true standard deviation.

I have provided the formula and excel method for both in the attached file.
Some would argue that N is correct others N-1.
I will leave it up to you.

ATB
Steve.
Formulas.xlsx
0
 

Author Comment

by:ExpExchHelp
ID: 39260980
Steve:

Absolutely fantastic... that is awesome.  

Thank you for providing both solutions for either approach... besides, I really like the presentation/visual in the XLS.

Again, thousand thanks!!!

EEH
0

Featured Post

Free Tool: Path Explorer

An intuitive utility to help find the CSS path to UI elements on a webpage. These paths are used frequently in a variety of front-end development and QA automation tasks.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This article will guide you to convert a grid from a picture into Excel format using Microsoft OneNote and no other 3rd party application.
Some code to ensure data integrity when using macros within Excel. Also included code that helps secure your data within an Excel workbook.
This Micro Tutorial will demonstrate in Google Sheets how to use the HYPERLINK function to create live links inside your spreadsheet.
This Micro Tutorial will demonstrate how to create pivot charts out of a data set. I also added a drop-down menu which allows to choose from different categories in the data set and the chart will automatically update.

597 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question