Designing user studies

Between subjects design - one group uses only one interface. - use it if you want to avoid ordering effect.

• Half of the users try out one interface.
• The other half tries out the other  interface .

Within subjects design - both groups use both  interfaces - this one avoids all the individual differences problem

Users already know a bit more about interfaces by the time they start using the second interface. To get more objective results in the end, both groups should start with different interfaces.