How is "ease of use" quantified?

December 12, 2006 6:26 PM

In product design, how do they quantify biomechanic or ergonomic "ease of use"? Do they measure forces or torques needed to use the product, and if so, how? Do they count the number of muscles involved in its use? Do they just try it out on a lot of people?

Let's say there are 2 kinds of jar openers: one which works by rotating your wrist, and one which works by rotating your shoulder. How are they compared when it comes to the physics and biology involved?

posted by unknowncommand to grab bag (9 comments total)

There is information, based on studies, showing standard human measurements and capabilities, split by gender, and sometimes by race (I think, this could have been some old stuff from the 50s and 60s). From these tables, things like light switch heights, doorknob heights etc are defined. In addition, these tables show standard forces and how they can be applied by the human body.
To expand on your example of the jar openers, there is a force required to open the jar. Rotating your wrist, this force could be near the maximum capable of a 'standard' female wrist. (I use gender because these tables are separated by gender.) Rotating the shoulder, this force is only a fraction of the maximum capable by the female shoulder as applied in this particular method. Therefore, the shoulder opener is better, as it's putting less strain on the muscles. In addition, a larger fraction will be able to use it, as there will always be those weaker (the elderly etc.)
posted by defcom1 at 6:56 PM on December 12, 2006 [1 favorite has favorites]

Actually, they don't do any of that. They just write "Ergonomic!" on the box. Usually, they also write "New!" or "Improved!" or some other words that they also think will increase sales.

There is no snark in this answer.

Consumer product design goes like this, as a general rule:

--someone designs a thing
--a manufacturer is enlisted to produce it
--they get a manufacturing sample of the item from the manufacturer
--the designer and perhaps a few other employees of the company try it out - look at the colors, examine the fit and the durability and construction of the product. Perhaps it is tested, by dropping it or sitting in it or using it in the manner it is expected to be used. Although some companies do significant amounts of testing, serious testing (more than just the designer and a couple of other people) is quite rare. Obviously, the more expensive the product, the more testing is done.
--if the designer is unhappy, alter the design, give it back to the manufacturer, and repeat
--if the designer is happy, it goes to marketing, who writes "Ergonomic!" and "New!" on it
--a million copies are made
--you read "Ergonomic!" on it, and purchase it

It may well be that the designer had some thought for how a human body would interact with the product. Shouldn't that be a part of almost all design? Or maybe they didn't - I've certainly seen chairs made out of spiky plexiglass, cups that were grossly too large or too small to drink from, etc. etc. There are "ergonomic chairs" that have no lower back support. There are "ergonomic chairs" that have huge lower back support, so that you'll be bent like a pretzel. Both designs cannot be the optimum amount of back support for the human back, yet both exist, and both are labeled ergonomic.

Either way, whether the designer actually gave a thought to ergonomics or just to beauty and cheapness of manufacturing, they didn't have anything to do with the writing of the word "Ergonomic!" on the product box, which was done by marketing.

(There certainly have been a variety of more-or-less scientific tests conducted to see how to optimize certain things for humans. However, you asked specifically about product design, and I'm telling you the complete truth when I say that ergonomics and the design of most consumer products have almost nothing to do with each other.)
posted by jellicle at 7:59 PM on December 12, 2006

When I went through extensive physical therapy associated with having both my hip joints completely replaced (ball and socket), I got interested in the devices the PT's were giving me to do a bunch of heretofore simple tasks, like putting on my socks. I have to this day, two different designs of sock aids, one based on a kind of garter hook assembly welded to a couple of long metal rods, and a far more effective one, consisting of a rolled up plastic sheet, and some bungi cords, over which you put the sock to be put on, and throw it at the foot desiring the sock, and then pull, sort of. You need 2 hours training to make it work, but it gets your sock on (sort of) in about 5 tries over 15 minutes, and keeps your artificial hip joint at a nice post op flexion angle maximum of about 75°, if you're careful.

So, while doing this, I started to pay attention to what the therapists were doing with knee replacement patients (poor, poor devils) and advanced arthritic patients. Lots of reachers, grabbers, towel slings and other devices to move stress points away from joints, and to spread loads to long bones (but never the middle of long bones) and away from joints. I learned that human joints suck, for people that don't die by 40. Cartilage, particular hyoid cartilage, is a fickle dream of the young, and ligaments and muscles can only be counted on for a few decades to support such silly designs as shoulders, spinal columns, and knees.

What the therapists showed me, in response to my larger questions, filled me with dread for aging. But when I asked them what data they had for designing strategy, treatment, and devices, they basically shrugged their shoulders (this in the periods I was recieving therapy 1994 and again in 1999). One senior department therapist connected with a major Atlanta hospital's orthepedic department told me that she felt they were years, if not decades away from understanding how best to instrument basic kitchen and cooking tasks for objective measurement, much less derive optimal treatments and assitive devices based on any such work. Kitchens, she said, are dangerous places for the healthy, and far worse for the disabled and impaired. Stirring a large pot of viscous material while standing, she said, involved up to 107 bones, 31 joints that she could identify, and 200+ coordinated movements of muscles. She recommended the then newly offered hand blenders, but admitted it was a purely common sense recommendation on her part, without any academic study behind it.

And she was right. I wasn't "healthy" again, until I could once again manage to cook in my significantly reorganized and improved kitchen. And ever since, I really, really think about the motions I must make in using a kitchen, whenever I move or otherwise have reason to set up a kitchen for myself. But a lot of this is just common sense. I minimize bending, and long reach motions. I make sure large and heavy things are stored below head height, and above waist height, so that I will naturally use my core muscles in moving them. I have definite "stations" for food prep, waste disposal, cooking, serving, and dish cleaning. I avoid silly architecuture like kitchen "islands" and ceiling mounted pot racks. And bathrooms get a lot of thought too, ever since I learned how deadly bathrooms can really be.
posted by paulsc at 9:02 PM on December 12, 2006

I used to design user interfaces, way back when. The field is a lot less scientific than you apparently think it is. At least for the kind of stuff I was doing it's not quantifiable at all.

But there are some principles. In terms of being "easy to use", the most important thing is that the tool vanish for an experienced user. By which I mean that the user ceases to be aware of the tool; it becomes part of the user.

Examples in common use: if you're a touch typer, you don't actually think about the keyboard when you're writing. When you drive a car, the car becomes an extension of your body; you don't consciously think about using the controls.

The ideal "easy to use" tool is a pair of pants. You don't operate a pair of pants, and 95% of the time you don't even think about the fact that you're wearing them. Pants go where you go, and automatically follow your legs. Pockets are placed so that they are readily accessible to your hands.

I don't know if there's any formal term for this. I call it "invisibility" or "submergence" and it was always the goal I set for myself in my user interface designs.

Five years ago I wrote about this at greater length in an essay titled "Beige is Beautiful".
posted by Steven C. Den Beste at 10:19 PM on December 12, 2006

By the way, there is a substantial field devoted to the kind of quantitative measurements you're talking about. It's called "Motion Study" and it was pioneered by Frank Gilbreth. But he concentrated mainly on trying to improve the efficiency of assembly lines.

It was Gilbreth who came up with the idea of having a nurse in surgery whose sole job was to pick up instruments to hand to the surgeon when he asked for them by name.
posted by Steven C. Den Beste at 10:24 PM on December 12, 2006

In most cases, it's somewhere in between defcom1 and jellicle. I worked with a few medical device design companies who have a dedicated staff engineer who deals with exactly these issues - how easy is it to use? Is it safe for the intended operator? These, of course, are expensive devices. I doubt that engineer designed the $50 "ergonomic" chair that we can buy from Target.
posted by muddgirl at 8:19 AM on December 13, 2006

I've studied usability some from a software standpoint. There are definitely metrics you can take, although some boil down to assigning subjective number ratings to essentially qualitative stuff.

Task completion time (new vs. experienced user, using primary handedness vs. off handedness, elderly vs. young, etc.)

Number of repetitions until the task becomes painful/fatigue is significant. This is qualitative, but for the same user, with both products, the "scale of fatigue" should be consistent so you can still use it as a basis for comparison.

If you have enough users and enough time, having a bunch of users each open a hundred jars in a row with the different openers should yield a pretty clear indication of which is better just by polling those users about which they prefer.
posted by juv3nal at 10:07 AM on December 13, 2006

I'm telling you the complete truth when I say that ergonomics and the design of most consumer products have almost nothing to do with each other.

If this were true, life would be a hell of a lot more frustrating and dangerous. Any competent product designer is going to take human factors into consideration. Of course, there are less than competent designers, and even the best ones don't always get their way. Manufacturing, mechanics, and marketing all impose limitations. But compare a curent product to one from a few decades ago and you'll see that improvements in technology often leads to ergonomic (and competative) advantages.

jellicle's timeline isn't exactly typical. Human factors and ergonomics are part of the entire design process. For less complicated projects (like a $50 office chair), designers and engineers can usually rely on common sense, experience, standards and regulations, and reference materials. Models and prototypes are often used, especially for more complicated projects (like a new type of jar opener) . Ideally, design issues are resolved before you ask for a sample from the manufacturer, since tooling costs (e.g. making the mold) are very expensive.

It's a fairly complicated subject, even if a lot of decisions are intuitive. Every body is different, which is why two different chairs can both be ergonomic. And design for disability is even trickier, because there are a lot of different types of disabilities. But it's great when a design meant to accomidate a small segment of the public is good design for the general population as well, like Oxo's Good Grips.

A good reference book to check out is The Measure of Man and Woman: Human Factors in Design. It's got an introduction that covers the techniques and history of anthropometry.
posted by hydrophonic at 12:14 PM on December 13, 2006

But compare a curent product to one from a few decades ago and you'll see that improvements in technology often leads to ergonomic (and competative) advantages.

OTOH, I bought a coffeemaker from cuisinart and it spills coffee when you pour it because the carafe is so badly designed. How crazy is that? (But it's stainless steel so it looks cool.)
posted by smackfu at 6:34 AM on December 14, 2006