Designing intersection flows
Avoiding problems with forms where users have
to choose between alternative ways to proceed
When forms give users the option to continue in two
or more alternative directions, such as registering as a new customer
or signing in as a returning one, unfortunate users will take the wrong
turn if it isn't unmistakably obvious which way they should go. In this
article, we'll take a look at a few intersection flows that have caused
Communicating to users how to fill out a form where each field has
to be filled out in a linear manner is relatively simple. Most users
even understand when we try to tell them that some fields are optional
and some are required. But when we ask users to choose between two or
more alternative ways of interacting with forms, things can go wrong
if we don't communicate the options in a clear and obvious way.
Intersections flows come in many guises. In the following we'll
look at a few that have caused users problems.
New or existing customer?
A classic intersection problem is the one below where users have to
sign in or register as a new customer.
Forms have a fatal attraction on users, and both new and returning
customers will start entering their e-mail address in the left column.
Few will notice the text telling that this is for returning customers
only. Some newcomers will start entering the password for their e-mail
account and some will think that they are creating a new password specifically
for this site. In both cases they will receive an error message telling
them that no account was found.
One solution that has proven to work quite well is to combine the
sign in and registration into one form using radio buttons. In this
interaction design, users are explicitly prompted to make their choice
between the two options.
In this new and improved design we actually still have a potential intersection
problem, since users can choose to have a new password send by clicking
the "Forgot your password" link. Since it's not uncommon
that people forget their password, it would make sense to integrate
this feature into the sign in form.
To lighten the burden for returning customers we can pre-select the
"I have a password" option if the user has signed in before.
Also, if the user starts entering a password, the "I have a password"
option should be selected automatically.
Search or select one or more categories
An interaction design that I've seen fail big time in usability
tests is the one below.
Here the user is asked to choose between one of two search strategies:
searching for an item or choosing one or more categories from the check
The problem with this design is that the users won't read the
text telling them that they have to choose between the two strategies.
Instead, they enter a search term, select a category from the list,
and hit either the Search or Next button.
One way to deal with this problem is to change the check box list
into a list of links. The users won't be able to select more categories
at the time, but in most cases they can do without it as long as they
can go back and select another category.
Search site or search Yellow pages?
Another intersection problem that I've seen fail in usability
tests is when two search functions are confused with each other. A typical
example is an intranet with separate site search and search for employees,
where both features are placed prominently on the front page because
they are both considered important to the intranet.
Even though it's clearly stated that this is the Yellow pages
and you have to enter the name of a person, people will try to use the
Yellow pages search for site wide searches. People don't stop
to explore the design in detail. If their task is to search the site
and they see a search button and an input field they will assume that
this will do the job. It's not that people don't understand
the distinction - they just don't notice.
To avoid confusion, we could somehow combine the two search functions.
One solution would be to turn the site search into a scoped search letting
users choose between searching the site and searching the Yellow pages.
Chances are that people won't notice the two options. But if
we include search results from the Yellow pages with the site search
results, this won't be a problem.
As said, intersection flows come in many guises. In this article,
we have looked at a few that I know have caused problems for users.
There is a potential problem if forms are involved and users have
to choose between this and that in order to proceed. We should be alert
if two or more forms are present on the same page, i.e. if there are
two or more sets of input fields with each their submit button - especially
if they are placed close to each other and if they work in a similar
There seems to be two ways to eliminate intersection problems. If
possible, get rid of options which aren't mission critical. If
this isn't possible, combine the options into one clear dialogue.
Filling out forms is like drive-by shooting. We cannot expect people
to read our instructions - not even bold headings and labels above
the input fields. To avoid confusion, our interaction designs should
communicate the options that the users have in a very clear and obvious
Text: Henrik Olsen