The validity of such evaluations depends on the purpose of the evaluation. Laboratory evaluations support development of a working prototype, but contextual evaluations support development of a working product by showing what really happens in the field. For example, laboratory evaluation of communication software may assess if users are able to select a symbol from a selection set, whereas in contextual evaluation additional aims of the evaluation may be to investigate whether a communication device can be used for discussions or if users increase their social circles or improve their discussion skills. Contextual evaluations are highly valid from rehabilitative point of view because they give feedback from those real situations which AT is intended to target. In addition, contextual evaluation raises service related problems which retailers may face and serves as a way for industrial partners to learn about the necessary product related services.
Ethical issues are important in both laboratory and contextual evaluations, but in different ways.
In laboratory evaluation, the emphasis is on whether participants are asked to do anything which may have any adverse consequences for them, either immediately or in the longer term. This can range from the stress of being asked to do tasks which are actually impossible to complete, or the boredom of undertaking many repetitive tasks. In contextual evaluations, expectations for a prototype may be very high among users and they tend to expect services similar to those for real products. Difficulties in use and any delay in maintenance can cause frustration. Therefore the whole project team has to commit themselves to a contextual evaluation and take responsibility for providing a realistic system and service to the users.