Our booking journey WILL require getting the exact age of any children added to the booking due to tax reasons. We are doing that by providing dropdowns to select the ages of these children.

We don’t have the data to estimate what a good default age is. Therefore if we was to have a default age it would be set at ‘0’ or ‘<1’. We are also testing the initial state of the dropdown as ‘-‘ where the user has to select an age before continuing with journey.


A - If the dropdown is default is ‘0’ or ‘<1’ Could the user ‘skip’ the age selection and complete their booking with incorrect child ages? This affects the price and could frustrate users further down the journey.

B - if the dropdown is ‘-‘ Does this create unnecessary interaction cost? Especially if the alternative state could be more accurate


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Would you prefer A or B?

Is there any findings over the impact of immediate friction against user created issues further down the journey (due to lack of error prevention). Also considering the peak end rule and error prevention which could mean option B is preferred.

  • I would consider more options: Using a "?" as default value for the dropdowns complements the question "Age of children". Or use "0" as it implies a faulty or reset value. But maybe that's just trying to fix something that is better off with a less ambiguous replacement. Have you tried other concepts?
    – jazZRo
    Commented Sep 4, 2020 at 7:27

3 Answers 3


We don’t have the data to estimate what a good default age is.

Even if you had data on what the most frequently selected child's age is, it would not make sense to preselect this as the default. There is no such thing as a "default age" of a child. Even if you happened to preselect the correct age, I would think it was very weird for you to automatically *know* my child's age before I told you.

You are correct that this would be frustrating for the user to have to fix the default selections they mistakenly skipped past, so the form should require a user's action to fill these fields. Initially showing an obvious non-answer until the user makes their selection is a common pattern. Personally, considering the real estate available in your design, a hyphen seems reasonable and not too unexpected.

  • I think defining the four states as <1 leads to misinterpretation that the passenger will be traveling with four children under one year of age.
  • Placing a - does not indicate at first glance which are the parameters to choose, creating confusion.

I would place the ratio of parameters to choose so the dropdown menu shows an indeterminate number and the user is forced to choose a specific number

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Ignore the specifics, preventing the user from making an error by ensuring what they enter initially is valid would be preferred over letting them proceed with an error (#5 in NNGroup's Usability Heuristics: https://www.nngroup.com/articles/ten-usability-heuristics/)

Looking at the specifics three things jumped out to me:

  1. As maxathousand says, there is no sensible default for an age. You could argue setting 1 or 17 might be an approach but if the user is not made to select, there will be some who don't and then effectively pass validation with an error present.
  2. You say "Due to tax reasons" but no more detail, I'd be very surprised if the tax reasons don't include grouping ages into buckets (0-1, 1-5, 5-12, 12-17 or similar) Perhaps you could do some more digging here to see if there is a way you can group data entry and make it quicker and simpler for the user.
  3. You also say you're using dropdowns for this task. You might want to question whether this is the best approach. You might want to consider a text field to avoid a long list of options which would potentially have a lower interaction cost.

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