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Our interface is using a slider which allows users to alter a price from a preset recommended price.

Alongside this we are showing the recommended price, the new altered price and, by request of the users, we are also showing the percentage increase or decrease.

Does anyone know if it would better to show this percentage increase as:

  • The recommended price as 100% so any increase would be above 100% e.g. 110%, any decreases would be below 100% e.g. 90%, or;
  • The recommended price as 0% so any increase would be above 0 e.g. +10%, any decreases would be below 0% e.g. -10%.

Which method would be more user friendly and aid usability?

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This sounds like a question that would be better answered by running an A/B test. –  zzzzBov Aug 6 '12 at 13:49
1  
Ask the users, especially since they made the request. –  Joshua Drake Aug 6 '12 at 15:44
    
Why not treat the base price as 100% (instead of zero) and increase/decrease as +10% or -10%? I think that's more intuitive, if you treat base price as 0, it somehow might confuse the user that the price is 0 i.e FREE? –  Ades Aug 8 '12 at 6:04

5 Answers 5

up vote 15 down vote accepted

I think that treating the current price as 0% would be much more intuitive to a larger section of your users.

If you treat your base price as 100% and display relative prices as 120% or 80%, a user might have to visualize the result as 120-100=20% increase or 80-100=20% decrease. The point is that this cognitive strain can be avoided by doing the calculation for the user and displaying results as 10% increase or 10% decrease.

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But couldn't you just as easily say that using +10% creates mental strain because the user is trying to visualize the result as 100+10%? –  Jimmy Breck-McKye Aug 6 '12 at 12:13
    
The final price would be displayed too, which is the most important thing. I don't think it's beneficial for the user to know that the price is 110% of the original price so therefore that strain won't occur. –  Fraser Aug 6 '12 at 13:31
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@Fraser - well, it depends on the context. Maybe if this is a retailer looking to manage margins and offers, it could be important. Then again, if it's just to handle prices for a stock application, then it wouldn't. Depends on the context. What IS the context, anyway? –  Jimmy Breck-McKye Aug 6 '12 at 15:35

I think your question depends on how you word the label. If the label says percentage increase/decrease then you should show the % change (i.e. 10%) but if the label suggests the % is a % of the total price then 110% is correct. I think the latter will confuse people as I can't think of a plain-English name for the label. Most people will expect the 10% increase to be shown rather than 110% of original value, and the label "Price increase decrease" makes a lot more sense.

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I don't envision there being a label. The percentage change would appear directly above the handle of the slider with an instant feedback loop upon changing. –  Fraser Aug 6 '12 at 9:24
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ah, in this case I would certainly go with +10% and -10%. Maybe double the impact with a green/red indicator for increase/decrease respectively. Fails some colourblind tests but it is just supplementary UX and not vital to use –  TJH Aug 6 '12 at 9:26

I think there is no way to answer this question other than by user testing. It would really depend on your audience which way of representation would be preferred. I would think that the -10%, +10%, 0% (considder changing for "recommended price" or "no change" or something like that in that case).

However, is there anyone stopping you from showing both representations? You could considder something like this:

mockup

download bmml source – Wireframes created with Balsamiq Mockups

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There's a convention for this. Retail stores market sales at a 20% discount not at 80% price. This convention is everywhere and most people would probably expect to see prices changed this way.

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don't implement all wants that came up during testing. that's how you get spaghetti UI. user testing is good but don't expect those to be your ultimate answers. you have to choose the right mix with good consistency. in this specific case i'd hesitate to provide feedback as two different numbers refering to same quantity. i'd ditch the percentage figures altogether unless you are meant to use that for something.

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