Google Answers Logo
View Question
Q: Minitab - calculating standard deviation of grouped data ( No Answer,   0 Comments )
Subject: Minitab - calculating standard deviation of grouped data
Category: Science > Math
Asked by: _len_-ga
List Price: $10.00
Posted: 16 Jul 2003 06:15 PDT
Expires: 15 Aug 2003 06:15 PDT
Question ID: 231578
How do I calculate a standard deviation of grouped data in Minitab?

Request for Question Clarification by elmarto-ga on 18 Jul 2003 10:34 PDT
Hello len,
Just to make sure I'll give you the correct answer, does your
spreadsheet look something like this?

Year    Sales
2000     100
2000     150
2000     130
2001     210
2001     250
2002     200

so the "groups" here would be 2001 and 2002. What you want to do is
calculate the standard deviation of elements in group 1 and the
standard deviation of elements in group 2?

Best regards,

Clarification of Question by _len_-ga on 18 Jul 2003 12:01 PDT
Thanks for the question.  The grouping is based on a attribute rather
than a date.  I'm not sure it makes any difference, but it'd probably
better if I explain it.

Suppose I'm manufacturing widgets every day.  The time it takes to
make widgets is variable, though, for a variety of reasons we don't
care about.  Suppose I measure the amount of time it takes, on
average, to make widgets each day, and it looks like this:

            Widgets         Seconds per
Day           Made             Widget
-----       -------         -----------
 1            100               60
 2             92               71
 3            115               56
 4             85               63
 5             72               57
 6             60               55
 7             55               50

I don't know how long it takes, for example, to make any individual
widget on Day 1.  All I know is that it took 6000 seconds (100 * 60)
to make 100 of them.  I believe this is what makes the widgets

Using the number of widgets made on each day, plus the average time
per day, I can calculate the weighted average for making widgets for
the entire week.  This is easy in Excel.  I can also calculate in
Excel the standard deviation if I know the formula for calculating the
std dev of grouped data.  My question is how I'd calculate the std dev
of this grouped data in Minitab.

Hope this helps.  Thanks very much.


Request for Question Clarification by elmarto-ga on 18 Jul 2003 19:37 PDT
Hi again, len!
OK, let me see if I understand. You're defining the widgets made in
day 1 as group 1, the widgets made in day 2 as group 2, etc, right? If
this is the case, then you can't calculate the std dev of each group
with the given data.

Let's take group 1. You only know that the average time is 60 seconds.
But since you don't know how much time each of the widgets took, you
can't calculate the std dev for this group. Same for the other groups.

If you wanted to calculate the weighted std dev across groups, I think
you would have to manipulate the columns in Excel, paste them in
Minitab and calculate the basic std dev. That is, you would have to
create a column with a hundred 60's, ninety-two 71's, etc. I don't see
any other way to this (some other researcher may, though).

Please do tell me if I didn't understand correctly what you meant by

Best wishes!

Clarification of Question by _len_-ga on 19 Jul 2003 04:14 PDT
Hi elmarto,

Yes, I'd thought of doing a cut-and-paste from Excel to Minitab with
one line per widget.  The only problem is that I've got more than a
million widgets to measure, and Excel can only handle a fraction of

I may end up sticking with my hand-made calculations in Excel.  I can
show how the calculations are derived, and I think that's more
important than seeing it done in a particular tool.


Request for Question Clarification by elmarto-ga on 19 Jul 2003 09:28 PDT
Hi len!
Well, here's my last attempt. Have you tried the "Make Patterned Data"
feature in the "Calc" menu? If you do't have many observations (i.e.,
many days in the example), this might work to make one observation per
widget. So if you have one hundred 60's and seventy 80's, choose in
the "Make Patterned Data" dialog box:

Store patterned data in:  some new column
From first value: 60
To last value: 60
In steps of: 1
List each value: 100 times

and the same for each day, always in a new column. Then you can use
the "Stack Columns" option in the "Manip" menu to make one long column
with all the new columns, and calculate the std dev of that column.

Please tell me if this worked you.

Best wishes!
There is no answer at this time.

There are no comments at this time.

Important Disclaimer: Answers and comments provided on Google Answers are general information, and are not intended to substitute for informed professional medical, psychiatric, psychological, tax, legal, investment, accounting, or other professional advice. Google does not endorse, and expressly disclaims liability for any product, manufacturer, distributor, service or service provider mentioned or any opinion expressed in answers or comments. Please read carefully the Google Answers Terms of Service.

If you feel that you have found inappropriate content, please let us know by emailing us at with the question ID listed above. Thank you.
Search Google Answers for
Google Answers  

Google Home - Answers FAQ - Terms of Service - Privacy Policy