For example,

Say the site is for searching cars for sale, one of the filters is "only show black cars", if there's a car listed which doesn't have a color specified, should it be included in the search results or not?

  • 1
    Might be worth repeating this comment from the asker on one of the answers: "I am building an aggregator that pulls listings from a number of sites, some which have missing data (or don't enforce the data as a required field)" - therefore, enforcing rules on data input alone isn't an answer Commented Mar 3, 2015 at 17:49

3 Answers 3


Some sites have "near miss" matches after their exact matches.

If a user has exhausted everything precisely matching their criteria but is still looking, there's a clear line and an explanation that this is the end of the results, then "near misses" sorted by how close to matching they are.

"Unspecified" would rank higher in this formula than "specified and wrong".

For example, it might look like this:


download bmml source – Wireframes created with Balsamiq Mockups

It's a good compromise because:

  • You don't get potentially irrelevant results polluting the good results, which would make it look like the filter's broken or the site has poor quality control
  • People who haven't found what they want after exhausting all the search results see things that might be relevant instead of a dead end
  • In cases where there are no matches, people see at least something (this requires good labelling)
  • Hard-to-match products that don't quite fit a taxonomy do get seen, and get seen by customers with hard-to-meet requirements

If there were no matches at all, you'd want a VERY large, prominent "Sorry, no results" box, around the size of those matches in the mockup above, so people don't see the (potentially relevant, potentially irrelevant) results before realising they're suggestions not matches, and then thinking something is broken.

  • This is a good approach. One situation it might not work as well for depends on how many results are going to be in the set. If there are many paginated pages of color-known results, would the unspecified results still be appended all the way at the end? I still like this solution, though. Commented Mar 4, 2015 at 3:40

No. For the user to actively specify a color, then see colors which do not match their specification risks confusion and a lack of confidence in the accuracy of the tool.

An alternative would be to add a sub-category of "Unspecified".

If you want to do something really interesting, crowd-source the data in the Unspecified category and ask users to say what color the car is.

  • 1
    How will they see the colours that don't match? As OP said colour is unknown! You are assuming images are attached this might not be the case!
    – Okavango
    Commented Mar 2, 2015 at 13:30
  • that did cross my mind actually, perhaps i'll give Amazon Mechanical Turk a go; mturk.com/mturk/welcome Commented Mar 3, 2015 at 2:50
  • It might also be worth looking into how Google Images's color filter works. Somehow when I search for "Car" then apply a color filter for "Blue" I'm given a whole bunch of obviously blue cars. You might be able to detect or at least make a "best guess" of what color those unspecified vehicles are and work them in. Commented Mar 4, 2015 at 3:44

Prioritize results with most relevant first:

You can mitigate the issue by:

  • Displaying this category of cars at the bottom of your search results so cars that do meet the full search criteria are presented first (higher relevance), only caveat here is to clearly emphasise visually and via adequate labelling the results that do not match the colour criteria but tick all other requirements.

  • Hiding the colour option within a collapsable filter

It is perfectly acceptable to collapse filters to just a label, providing a single link like View All Filters Source: Best Practices for Designing Faceted Search Filters

This will increase search accuracy and help conversions for the majority of users for whom colour is not the main focus. (approach used by Auto Trader)

enter image description here

Adding an option for unspecified or other ?

Overall not a good idea, consider the following (assuming that product count is dynamicly updated as in the example of auto trader):

  • When there is only limited number of cars with unspecified colour it would be a waste of precious page real-estate while also adding complexity to filtering options.

  • When there is a large number of cars with unspecified attributes "colour or otherwise" then an unspecified option erodes user confidence in the site and indirectly suggests that your customers don't provide full details about what they are selling.

The best approach is to present your results with clarity using clear and understandable filtering options and ideally:

“At every step in the search workflow, any visible filtering options should reflect only the inventory that is available.”

Source: Best Practices for Designing Faceted Search Filters

Instead of burdining your filtering options with an ambiguous option, rely on users to make a judgment call if they would like to contact the vendor if the car ticks all their other requirements.

Overall, the unspecified or other option is an anomaly because "category labels should accurately describe the information in the category" to help users anticipate what they will find.

This might be the result of technical constraints as you have highlighted or because of difficulties matching the search criteria, but the user should not be asked to do guess work as a result:

I am building an aggregator that pulls listings from a number of sites, some which have missing data (or don't enforce the data as a required field)

To conclude, filtering options are not only a search facility but also a navigational structure and labelling and navigation best practices should apply.

  • 2
    At first, I would go for that too but as a user, when I use a filter and it display me non related items, my though are : "well, these filter doesn't work well" and It tend to give me a bad feedback about a lot of things. I will use them anyway but with a feeling of bad experience, so If I find another website with good ones, it can make the difference. Can you force the user who create the classified ad ? Commented Mar 2, 2015 at 13:19
  • I somehow agree with @FrançoisDACQUIN; if the colour is unknown, the user may want to see the result, but it must be made very clear that "all results below this line" may or may not match the filter criteria. Possibly, don't even show those results immediately, but offer them via a link like "Show possible/unconfirmed matches". Google regularly thinks it knows better then me what I am looking for, and that auto-correction of search input regularly drives me crazy. No need to copy that bad habit for any filtering/search service. Commented Mar 2, 2015 at 13:56
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    @O.R.Mapper I agree, unconfirmed matches should be clearly distinguished from other results!
    – Okavango
    Commented Mar 2, 2015 at 14:04
  • How about using checkboxes or other such control to identify all "acceptable" controls, and have "other/unspecified" be one of the choices?
    – supercat
    Commented Mar 2, 2015 at 21:51
  • 1
    Unfortunately my situation is unique in that I am building an aggregator that pulls listings from a number of sites, some which have missing data (or don't enforce the data as a required field) - hence why the long term solution couldn't really apply Commented Mar 3, 2015 at 2:49

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