# Why do weight loss studies use the mean and not the mode?

**URL:** <https://boards.straightdope.com/t/why-do-weight-loss-studies-use-the-mean-and-not-the-mode/752477>\
**Category:** Factual Questions\
**Created:** [April 17, 2016, 5:01pm UTC](https://boards.straightdope.com/t/why-do-weight-loss-studies-use-the-mean-and-not-the-mode/752477 "2016-04-17T17:01:11Z")\
**Posts on this page:** 5\
**Page:** 2

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**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\
**Post date:** [April 18, 2016, 1:59pm UTC](https://boards.straightdope.com/t/why-do-weight-loss-studies-use-the-mean-and-not-the-mode/752477/21 "2016-04-18T13:59:49Z")

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Obviously if you use one number to characterize a distribution, it will “overstate” some samples and “understate” others.

If the distribution is reasonably close to a normal (Gaussian) distribution, reporting the mean and the standard deviation will be appropriate and sufficient.

If the data contains some outlier points that skew the mean, the median is a good alternative. If 10 people lost 2 pounds and 1 person _gained_ 20 pounds, the mean is a weight less of zero, but the median is 2 pounds.

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**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\
**Post date:** [April 18, 2016, 2:45pm UTC](https://boards.straightdope.com/t/why-do-weight-loss-studies-use-the-mean-and-not-the-mode/752477/22 "2016-04-18T14:45:35Z")

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> [@Septima](#):
>
> …snip…
> 
> I’m guessing the baseline is 5%, same as for giving up cigarettes or alcohol (number stolen from Penn and Tellers “Bullshit”, feel free to insert better numbers if you have them on hand), so anything above that would be interesting.

Well, we see this kind of thing happen 15 to 20 to 80% of the time. 🙂

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**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\
**Post date:** [April 18, 2016, 2:52pm UTC](https://boards.straightdope.com/t/why-do-weight-loss-studies-use-the-mean-and-not-the-mode/752477/23 "2016-04-18T14:52:37Z")

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If the number of people/cases/examples isn’t huge, and if the ‘raw data’ isn’t massive, you can take a number of people who most closely resemble a given subject and do a basic average, while realizing averages are composed of a range… and if 30 is the high end and 10 is the low end, the most you can hope for is somewhere in the range… if we’re talking about weight loss.

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**Author:** ![Septima](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@Septima](https://boards.straightdope.com/u/Septima)\
**Post date:** [April 18, 2016, 5:34pm UTC](https://boards.straightdope.com/t/why-do-weight-loss-studies-use-the-mean-and-not-the-mode/752477/24 "2016-04-18T17:34:27Z")

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[QUOTE=Blue Blistering Barnacle]  
Well, we see this kind of thing happen 15 to 20 to 80% of the time.  
[/QUOTE]

Huh? Who is seeing what happen?

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**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\
**Post date:** [April 18, 2016, 9:20pm UTC](https://boards.straightdope.com/t/why-do-weight-loss-studies-use-the-mean-and-not-the-mode/752477/25 "2016-04-18T21:20:13Z")

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> [@Septima](#):
>
> Huh? Who is seeing what happen?

Just a silly comment in response to the 5% bullshit comment. We would sometimes say this when we were pulling “statistics” out of thin air.

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