Sunday, December 31, 2006

Another funny cost/benefit example

This one would be funny if it weren't so dangerous. In some states, teen drivers are not allowed to have more than 1 or 2 passengers in the car. So to get around this rule, they have their friends ride in the trunk. Doing this at 5 mph to sneak into a drive-in movie is one thing, but doing it during normal driving, especially 65 mph on the highway, is very dangerous. But the teens do it because their perception of the risk is lower than the perceived benefit of transporting their friends.

So California passed a law making it illegal for anyone to ride in the trunk of a car. On its surface, it sounds like a funny law. But when you think of why they had to do it (increase the costs of this behavior), it makes perfect sense.

Looking at things differently

I am almost embarrassed to admit how much I 'live' human factors. Everything I see around me, I interpret in terms of how well it meets user needs as defined in context. So for example, when I am at the gym, they have an indoor track that has a simple rule. Users run clockwise Mon, Wed, and Fri and they run counterclockwise Tue, Thurs, and Sat. This is because running on a short loop puts a lot of pressure on the outside leg. So running different ways is better for you.

So why is the scheme MWF one way and TTS the other way? It seems that they are spreading the days around the week. If you go to the gym every day, this would be ideal. But if you look at real people, what gym schedules do you think are most common? Experts tell us that we shouldn't work out every day - it takes about 48 hours for our muscles to recover from a workout. So we should do each exercise every other day instead of consecutive days. Of course, this means that users who run on the track are probably running either MWF or TTS. So the way they designed this rule causes each person to run around the track the same way every time, exactly what the schedule is trying to prevent.

This error is caused by the gym management not thinking about how real users use their product. If you ask anyone naive to HF, they will probably go with the MWF and TTS schedules too. But when you point out the irony I describe above, they immediately realize the error. So how come the gym management never does?

Thursday, December 28, 2006

Tradeoff between safety and speed

I saw a great example of how workers sacrifice their safety to save time. Why do they do this when their safety is their own, whereas their labor profits their company? It is not a pure economic decision. In general, it is just the assumption that the loss in safety is not very big (even though they are often wrong about this) and saving time is a natural human objective, even when there is little direct benefit. And there may be some benefits in terms of making the boss happy and getting good evaluations.

So here is the example that I saw: lets call it the ladder wiggle. A contractor was near the top of a 15 foot ladder leaning onto the roof of a one-story storefront. He needed to move the ladder about a foot forward to reach what he was working on. It would have taken maybe 30 seconds to climb down the ladder, move it, and then climb back up. But instead, he grabbed onto the edge of the roof to support some of his body weight, and wiggled the ladder side to side and shuffled it forward. Watching this with some fascination, I estimated about a 10% chance that the ladder (and the worker) would fall. 10% is not bad, but is it worth saving 30 seconds? Apparently, it was to him.

The cognitive process is simple. There he was on the ladder and the most direct way to move it was the ladder wiggle. Rather than a cost/benefit analysis, which would have resulted in a safer solution, he evaluated his first option, determined the risk was acceptable, and did it. As with RPD decisions, it was not a comparison of alternatives.

Wednesday, December 13, 2006

Human Factors is a state of mind

As usual at the end of the semester I get students who tell me that they see the world in a whole new way after taking my human factors course. They way I (and many of my colleagues) teach Human Factors really does become a perspective rather than a set of theories or tools to use at work. On the very first day, I tell them that they will not only be better designers, but also better and dealing with friends, relatives, coworkers, and significant others. They don't believe me then, but by week 4 they sure do.

Maybe I should start a religion and become a preacher instead of a teacher???

Sunday, December 10, 2006

risk / safety tradeoff

We have known for a long time that many safety features do not actually make people safer because they use this opportunity to work faster/riskier/etc and thus revert to the individual's own risk tolerance (modified by external incentives such as productivity bonuses).

But there are also negative externalities to worry about. In a new study, Ian Walker at the University of Bath found that cyclists who wear helmets have a higher chance of getting hit by a car than those who do not. So does this mean that cyclists adjust to their added safety by riding more aggressively? It turns out the answer is no. The people who adjust their behavior is the driver. Drivers passing cyclists with helmets drive closer to the bike than drivers passing cyclists without helmets. So even though the biker doesn't change his/her behavior, his/her risk goes up.

An earlier study by Sam Pelzman found that drivers who wear seat belts drive more aggressively. So their risk stays the same overall. But the people around them have higher risk. So the total system risk is higher. Paradoxically, adding safety features increases total system risk.

There is not enough data to know how significant this effect is in general or whether it would really be better to get rid of some safety features to increase safety. Sounds like a good research proposal for an ambitious safety researcher.

Human Factors and biblical interpretation

I had a very interesting conversation with some students last night. Normally, I don't like to bring up religion at dinner because it tends to be an emotional topic. But one student seemed really interested in my view, so I thought I would share it with her. I was explaining that something in the brain's function likely evolved because of the needs of humans as the emerged from the African savannah.

She asked me if I believed in evolution or creation. I told her both, and the explanation is pure human factors. I believe that G-d created evolution. It makes much more sense to set in place a system of physical laws and cosmic raw materials than it does to preset each and every species of animal and plant.

So the next question of course is "Why does it say in the bible that it took six days etc?" But this is where human factors comes in. Imagine the state of human knowledge at the time that G-d was explaining the history of the world to Moses on Mt Sinai. Moses would not have understood any of it. I am sure that G-d would have loved to explain how the double helix structure of DNA leads to natural selection, but it would not have been a good use of time. So he explained in using stories in the same way that scientists explain their work to their families, or parents explain sex to young children. And then Moses told the rest of the Hebrews, who told their kids, who told their kids etc for about 1500 years before anyone wrote it down.

Given this reality, it is remarkable how many things do fit the historic record, not the several inconsistencies. When my students copy class notes from friends after they miss a class, there are huge discrepancies. I can't imagine going 1500 years without the content changing completely.

So, G-d created evolution, told Moses the story allegorically in a way he could understand, and 1500 years later, we get Adam and Eve, Noah's flood, etc. I don't see how it could be any other way.