All posts filed under “Poka-yoke

Eight design patterns for errorproofing

Go straight to the patterns

One view of influencing user behaviour – what I’ve called the ‘errorproofing lens’ – treats a user’s interaction with a system as a set of defined target behaviour routes which the designer wants the user to follow, with deviations from those routes being treated as ‘errors’. Design can help avoid the errors, either by making it easier for users to work without making errors, or by making the errors impossible in the first place (a defensive design approach).

That’s fairly obvious, and it’s a key part of interaction design, usability and human factors practice, much of its influence in the design profession coming from Don Norman’s seminal Design of Everyday Things. It’s often the view on influencing user behaviour found in health & safety-related design, medical device design and manufacturing engineering (as poka-yoke): where, as far as possible, one really doesn’t want errors to occur at all (Shingo’s zero defects). Learning through trial-and-error exploration of the interface might be great for, say, Kai’s Power Tools, but a bad idea for a dialysis machine or the control room of a nuclear power station.

It’s worth noting a (the?) key difference between an errorproofing approach and some other views of influencing user behaviour, such as Persuasive Technology: persuasion implies attitude change leading to the target behaviour, while errorproofing doesn’t care whether or not the user’s attitude changes, as long as the target behaviour is met. Attitude change might be an effect of the errorproofing, but it doesn’t have to be. If I find I can’t start a milling machine until the guard is in place, the target behaviour (I put the guard in place before pressing the switch) is achieved regardless of whether my attitude to safety changes. It might do, though: the act of realising that the guard needs to be in place, and why, may well cause safety to be on my mind consciously. Then again, it might do the opposite: e.g. the steering wheel spike argument. The distinction between whether the behaviour change is mindful or not is something I tried to capture with the behaviour change barometer.

Making it easier for users to avoid errors – whether through warnings, choice of defaults, confirmation dialogues and so on – is slightly ‘softer’ than actual forcing the user to conform, and does perhaps offer the chance to relay some information about the reasoning behind the measure. But the philosophy behind all of these is, inevitably “we know what’s best”: a dose of paternalism, the degree of constraint determining the ‘libertarian’ prefix. The fact that all of us can probably think of everyday examples where we constantly have to change a setting from its default, or a confirmation dialogue slows us down (process friction), suggests that simple errorproofing cannot stand in for an intelligent process of understanding the user.

On with the patterns, then: there’s nothing new here, but hopefully seeing the patterns side by side allows an interesting and useful comparison. Defaults and Interlock are the two best ‘inspirations’ I think, in terms of using these errorproofing patterns to innovate concepts for influencing user behaviour in other fields. There will be a lot more to say about each pattern (further classification, and what kinds of behaviour change each is especially applicable to) in the near future as I gradually progress with this project.

 

Defaults

“What happens if I leave the settings how they are?”

■ Choose ‘good’ default settings and options, since many users will stick with them, and only change them if they feel they really need to (see Rajiv Shah’s work, and Thaler & Sunstein)

■ How easy or hard it is to change settings, find other options, and undo mistakes also contributes to user behaviour here

          Default print quality settings  Donor card

Examples: With most printer installations, the default print quality is usually not ‘Draft’, even though this would save users time, ink and money.
In the UK, organ donation is ‘opt-in’: the default is that your organs will not be donated. In some countries, an ‘opt-out’ system is used, which can lead to higher rates of donation

Interlock

“That doesn’t work unless you do this first”

■ Design the system so users have to perform actions in a certain order, by preventing the next operation until the first is complete: a forcing function

■ Can be irritating or helpful depending on how much it interferes with normal user activity—e.g. seatbelt-ignition interlocks have historically been very unpopular with drivers

          Interlock on microwave oven door  Interlock on ATM - card returned before cash dispensed

Examples: Microwave ovens don’t work until the door is closed (for safety).
Most cash machines don’t dispense cash until you remove your card (so it’s less likely you forget it)

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Lock-in & Lock-out

■ Keep an operation going (lock-in) or prevent one being started (lock-out) – a forcing function

■ Can be helpful (e.g. for safety or improving productivity, such as preventing accidentally cancelling something) or irritating for users (e.g. diverting the user’s attention away from a task, such as unskippable DVD adverts before the movie)

Right-click disabled

Example: Some websites ‘disable’ right-clicking to try (misguidedly) to prevent visitors saving images.

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Extra step

■ Introduce an extra step, either as a confirmation (e.g. an “Are you sure?” dialogue) or a ‘speed-hump’ to slow a process down or prevent accidental errors – another forcing function. Most of the everyday poka-yokes (“useful landmines”) we looked at last year are examples of this pattern

■ Can be helpful, but if used excessively, users may learn “always click OK”

British Rail train door extra step

Example: Train door handles requiring passengers to lower the window

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Specialised affordances

 
■ Design elements so that they can only be used in particular contexts or arrangements

Format lock-in is a subset of this: making elements (parts, files, etc) intentionally incompatible with those from other manufacturers; rarely user-friendly design

Bevel corners on various media cards and disks

Example: The bevelled corner on SIM cards, memory cards and floppy disks ensures that they cannot be inserted the wrong way round

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Partial self-correction

■ Design systems which partially correct errors made by the user, or suggest a different action, but allow the user to undo or ignore the self-correction – e.g. Google’s “Did you mean…?” feature

■ An alternative to full, automatic self-correction (which does not actually influence the user’s behaviour)

Partial self-correction (with an undo) on eBay

Example: eBay self-corrects search terms identified as likely misspellings or typos, but allows users the option to ignore the correction

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Portions

■ Use the size of ‘portion’ to influence how much users consume: unit bias means that people will often perceive what they’re provided with as the ‘correct’ amount

■ Can also be used explicitly to control the amount users consume, by only releasing one portion at a time, e.g. with soap dispensers

Snack portion packs

Example: ‘Portion packs’ for snacks aim to provide customers with the ‘right’ amount of food to eat in one go

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Conditional warnings

■ Detect and provide warning feedback (audible, visual, tactile) if a condition occurs which the user would benefit from fixing (e.g. upgrading a web browser), or if the user has performed actions in a non-ideal order

■ Doesn’t force the user to take action before proceeding, so not as ‘strong’ an errorproofing method as an interlock.

Seatbelt warning light

Example: A seatbelt warning light does not force the user to buckle up, unlike a seatbelt-ignition interlock.

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Photos/screenshots by Dan Lockton except seatbelt warning image (composite of photos by Zoom Zoom and Reiver) and donor card photo by Adrienne Hart-Davis.

Salt licked?

Salt shakers. Image from Daily MailSalt shakers. Image from Daily Mail

UPDATE: See the detailed response below from Peter of Gateshead Council, which clarifies, corrects and expands upon some of the spin given by the Mail articles. The new shakers were supplied to the chip shop staff for use behind the counter: “Our main concern was around the amount of salt put on by staff seasoning food on behalf of customers before wrapping it up… Our observations… confirmed that customers were receiving about half of the recommended daily intake of salt in this way. We piloted some reduced hole versions with local chip shops who all found that none of their customers complained about the reduced saltiness.”

A number of councils in England have given fish & chip shops replacement salt shakers with fewer holes – from the Daily Mail:

Research has suggested that slashing the holes from the traditional 17 to five could cut the amount people sprinkle on their food by more than half.

And so at least six councils have ordered five-hole shakers – at taxpayers’ expense – and begun giving them away to chip shops and takeaways in their areas. Leading the way has been Gateshead Council, which spent 15 days researching the subject of salty takeaways before declaring the new five-hole cellars the solution.

Officers collected information from businesses, obtained samples of fish and chips, measured salt content and ‘carried out experiments to determine how the problem of excessive salt being dispensed could be overcome by design’. They decided that the five-hole pots would reduce the amount of salt being used by more than 60 per cent yet give a ‘visually acceptable sprinkling’ that would satisfy the customer.

OK. This is interesting. This is where the unit bias, defaults, libertarian paternalism and industrial design come together, in the mundanity of everyday interaction. It’s Brian Wansink’s ‘mindless margin’ being employed strategically, politically – and just look at the reaction it’s got from the public (and from Littlejohn). A BBC story about a similar initiative in Norfolk also gives us the industry view:

A spokesman for the National Federation of Fish Friers called the scheme a “gimmick” and said customers would just shake the containers more.

Graham Adderson, 62, who owns the Downham Fryer, in Downham Market, said: “I think the scheme is hilarious. If you want to put salt on your fish and chips and there are only four holes, you’re just going to spend longer putting more on.”

I’m assuming Gateshead Council’s research took account of this effect, although there are so many ways that users’ habits could have been formed through prior experience that this ‘solution’ won’t apply to all users. There might be some customers who always put more salt on, before even tasting their food. There might be people who almost always think the fish & chips they get are too heavily salted anyway – plenty of people, anecdotally at least, used to buy Smith’s Salt ‘n’ Shake and not use the salt at all.

And there are probably plenty of people who will, indeed, end up consuming less salt, because of the heuristic of “hold salt shaker over food for n seconds” built up over many years of experience.

Overall: I actually quite like this idea: it’s clever, simple, and non-intrusive, but I can see how the interpretation, the framing, is crucial. Clearly, when presented in the way that the councils media have done here (as a government programme to eliminate customer choice, and force us all down the road decided by health bureaucrats), the initiative’s likely to elicit an angry reaction from a public sick of a “nanny state” interfering in every area of our lives. Politicians jumping on the Nudge bandwagon need to be very, very careful that this isn’t the way their initiatives are perceived and portrayed by the press (and many of them will be, of course): it needs to be very, very clear how each such measure actually benefits the public, and that message needs to be given extremely persuasively.

Final thought: Many cafés, canteens and so on have used sachets of salt, that customers apply themselves, for many years. The decision made by the manufacturers about the size of these portions is a major determinant of how much salt is used, because of the unit bias (people assume that one portion is the ‘right’ amount), and, just as with washing machine detergent, manipulation of this portion size could well be used as part of a strategy to influence the quantity used by customers. But would a similar salt sachet strategy (perhaps driven by manufacturers rather than councils) have provoked similar reactions? I’m not sure that it would. ‘Nanny manufacturer’ is less despised than ‘nanny state’, I think, certainly in the UK.

What do you think?

Hard to handle

Open door using outside handle

Open door using outside handleBritish Rail’s drop-the-window- then-stick-your-hand-outside- to-use-the-handle doors puzzled over by Don Norman in The Design of Everyday Things are still very much around, though often refurbished and repainted as with this delightful/vile pink First Great Western-liveried example.

I’m assuming that this design was intended to introduce an extra step into the door-opening procedure, a speed-hump, if you like, to make it less likely that a door was opened accidentally while the train was in motion (before central door locking was introduced – which makes it less necessary). From a usability point of view, we might immediately dismiss any system which has to have such detailed instructions to inform the user about performing such a simple task, but it’s certainly interesting to consider this kind of poka-yoke. Being forced to lowering the window to get to the handle is almost like a modal ‘Are you sure you want to delete this file?’ dialogue box.

Open door using outside handle

However, other concerns come into play and now need to be considered in addition: this sticker suggests keeping the window closed to cut drag and save fuel, but as I walked along the train, almost all these windows were dropped down, left in that position by the last person to close the door. The urgency of scrabbling to lower the window, stick your hand out and use the handle, with a crowd of commuters behind you probably overwrites any intentions to close the window again engendered by the ‘Make a small change’ sticker.

Open door using outside handle

Lights reminding you to turn things off

Standby indicators - Duncan DrennanStandby indicators - Duncan Drennan

Duncan Drennan
, who writes the very thoughtful Art of Engineering blog, notes something extremely interesting: standby lights, if they’re annoying/visible enough, can actually motivate users to switch the device off properly:

Our DVD player has (to me) the most irritating standby light that I have ever seen on any device. When on, the light is constantly illuminated, but when in standby the light flashes continuously (at a slow rate). This drives me mad, but results in an interesting action – it causes me to turn it off at the plug when I am not using it (which is most of the time). Suddenly one little flashing light has resulted in more energy saving than having no light.

As he notes, designing a system with an indicator which actually draws power to inform you of… ‘nothing’ … actually may not be as inefficient as a from-first-principles efficiency design process would suggest, because of that human reaction. Similarly to the Static! project’s Power-Aware Cord, you may need to use a little extra energy to make people realise how much they’re using without thinking. Although:

There is one problem with this, it only works on people who care. If I did not care about saving energy, then I would just leave the laptop plugged in and the DVD player on. That means that you have to consider how your users will handle this kind of subtle feedback and determine whether turning the light off, or encouraging unplugging, results in more energy savings.

Sometimes the most obvious design decisions may not be the ones which result in the greatest energy saving.

This is a very astute observation indeed.

Are there any other examples where this sort of effect can be usefully employed? How similar is this to the ‘useful landmine’ concept where you deliberately force/provoke/annoy yourself into taking actions you otherwise wouldn’t bother/would forget to do?

Design with Intent presentation from Persuasive 2008

EDIT: I’ve now added the audio! Thanks everyone for the suggestions on how best to do it; the audio is hosted on this site rather than the Internet Archive as the buffering seemed to stall a bit too much. Let me know if you have any problems.

I’ve put my presentation from Persuasive 2008 on SlideShare, – because of the visual style it really needs to be listened to, or viewed alongside the text (below, or in the comments when viewing it on the SlideShare site). Alternatively, just download it [PPT, 11.6 Mb] – it comes with the notes.

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Un-hiding an affordance

Steps in Dawlish, Devon

Steps in Dawlish, Devon

These (pretty shallow) steps in Dawlish, Devon, have been labelled as such, presumably because without this, some visitors wouldn’t notice, and would run, cycle or wheelchair down them and hurt themselves or others. Painting a white line along the edge is a common way of improving visibility of steps, but actual labelling is fairly unusual.

There is some argument that having to label an affordance in this way, rather than it being self-evident (e.g. by making the steps deeper, or putting a handrail, or something), is ‘bad design’, but I’m not sure one way or the other: from a utilitarian point of view, enormous labelling, however ‘ugly’, is probably a surer bet than providing subtle ‘cues’. Nevertheless, the poka-yoke approach would be to design out the problem entirely: make the whole thing a full-width ramp like the section at the side.

A diagram in Bill Gaver‘s classic paper ‘Technology Affordances‘ [PDF, 647 kb] sets out very clearly the importance of an affordance being perceived as such by a user:

From 'Technology Affordances' , William Gaver

In this case we have a hidden affordance (not deliberately hidden) which has been un-hidden by the label – similar to (though not as funny as) the ‘This is a Mop Sink‘ example from Michael Darnell’s fantastic BadDesigns.com:

This is a Mop Sink (image from www.baddesigns.com)