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# Meaning of "Man Months"

Posted on 2004-08-04
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Anybody here knows what is "Man Months" in terms of Management Metrics and percentage work rendered?

Anybody can explain to me what really "Man Months" mean? Is it the Number of People working for a certain task? or the total number of Hours worked with the people of a certain task?

Anybody?
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Question by:girlswants_me
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Expert Comment

Hi girlswants_me,

1 man month = 1 man working on the task for 1 month
3 men worling on 1 task for 1 month = 3 man months

I hope you get the idea ... it is an absolute term, not relative or percentage

Sunnycoder
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Author Comment

I was just confused because there are only 4 people in the group and the metrics is having 8 man months for the year. how can you explain this?
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Expert Comment

hello
"I was just confused because there are only 4 people in the group and the metrics is having 8 man months for the year. how can you explain this? "

sonny gave a correct answer for man month meaning. I am not sure what you mean by metrics...but as an example if the 4 people work on a project for 2 months then it
would be an 8  man month project during the year not for the year...or it might be that
only one person works on the project for 8 months. etc etc etc....

I think person month might be politically correct since females have been known
to contribute to a project.

the man month concept works well for  budgeting type analysis, but it can be
misleading for some situations. When a software development project is behind
schedule it is usually suggested by management to put more people on the task...

At most meetings where this is proposed someone will make the observation that:
" You cannot get 9 women to make a baby in one month ."

leojl
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Expert Comment

>I was just confused because there are only 4 people in the group and the metrics is having 8
>man months for the year. how can you explain this?

All of them will not be working on the same task all year long ... What it means is that during one year, among these 4 ppl (total 12X4=48 man months), 8 man months will be spent on this task
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Accepted Solution

Arthur_Wood earned 125 total points
A Man-Month assumes the 1 Man is working FULL_TIME (40 hours per week for 4 weeks) on the Task.  So 1 Man-Month of effort is a TOTAL effort of 160 MAN-HOURS

If a Task has a Length of 12 Months, and the Level of effort is set to 4 Man-Months, then that task will require

1 man to work 1/3 time (13.33 hours per week for 4 weeks each month or any other combination that comes up to 43.33 hours of effort per month) for the 12 months
OR
2 men to COMBINE their time to equal 43.33 hours of effort per month for 12 months

aor any other combination of workers to account for a TOTAL effort over the 12 Months of 1920 MAN-HOURS (1 man working for 1 hour) of effort over the course of the 12 months.

The big flaw with using Man-Month as a Metric is the assumption that by using MORE men on the task will result in the task being completed FASTER (2 Men doing a 1 Man-Month task should finish in 1/2 the time of 1 Man on the same task), and by this logic, since having a BABY requires 9 WOMAN-MONTHS of effort, then if you put 9 women to work on the Task, you should get  the Baby in 1 Month - yeah, right - tell that to my wife.

You need to read the book "The Mythical Man-Month" ( a classic) by Fred Brooks:

http://www.amazon.com/exec/obidos/tg/detail/-/0201835959/104-4996356-2176715?v=glance

AW
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Author Comment

Arthur_Wood,

I was so impressed with what you said. Thank you very very much.
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Expert Comment

thank you and glad to be of assistance.

AW
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Expert Comment

>>The big flaw with using Man-Month as a Metric is the assumption that by using MORE men on the task will result in the task being completed FASTER (2 Men doing a 1 Man-Month task should finish in 1/2 the time of 1 Man on the same task), and by this logic, since having a BABY requires 9 WOMAN-MONTHS of effort, then if you put 9 women to work on the Task, you should get  the Baby in 1 Month - yeah, right - tell that to my wife.

YOUR logic is flawed. since having a baby requires 9 woman-months of effort, then if you put 9 women to work on the tast, you WILL get a baby in 1 month. however, you would be hard pressed to get 9 women to each work on a piece of the baby. here's the logic behind the man month. 1 man can paint a house in 2 months. then 2 men will be able to do it in 1 month. 4 men will do it in .5 month. your baby example is flawed because having a baby is not something that multiple people can work on at the same time. its a one woman job (after the little part that one man plays in the beginnig, which is a negligable amount of time spent on this, especially when compared to the amount of time the woman spends). you should pick a job that multiple people can do at the same time.
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