Why you shouldn’t use Man-Hours


Props to these folks for being safe ^^

It’s Sexist

No questions here, plain and simple. Don’t other genders work? or should we discriminate against them by using a different time units like women-minute? or women-47minutes (see what I did there ; ) )

It creates the wrong mental image

When I was 12 or 13, I had a teacher who would say if we all came to class on time (we were usually 5-10 minutes late) we would save 16 hours a day! and everyone would go mental because 16 hours a day is a lot of time (it’s in fact 67% of it).

But I always had trouble with this concept, in my mind I would only save 30 minutes or so because that amount of time was relevant to me. I of course couldn’t articulate what my problem was with this concept at the time (plus, I thought I would save 30 minutes by going to class late) until I thought about it today and figured it out.

The problem in short is the denominator, we always talk about these huge numbers when talking about man-hours because our goal is to impress people with how much can be gained by small changes. For example this old news paper article argues Milwaukee will save 40,400 man-hours as a result of an expressway. As a reader, you would say “wow, we should definitely invest in this project because it’ll save us 4.6 years a day! But in my opinion that’s all wrong. The denominator here is the number of man-hours in a day which is 15,297,408 (Milwaukee population in 1950 was 637,392) making the change a 0.26% improvement.

That being said, this 0.26% change might be worth the money but that’s a different story.

Conclusion (for the sake of it)

Data is a powerful tool. It’s like “scientific fact”, if you tell someone something is a scientific fact they’re going to believe you. mostly because they don’t think they’ll understand the underlying logic (or they simply don’t have the time to go over it). But I also think it’s a moral burden to not confuse, mislead or otherwise trick people into believing your cause. This can be very easily done with numbers (mostly very large or very small). So don’t tell your students to come to class early.

Just to give you a final example, if every person in the united states didn’t read this article we would collectively save 50.57 years. so please don’t waste national resources surfing the web.


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