Evaluation is central in research and development of information retrieval (IR). In addition to designing and implementing
new retrieval mechanisms, one must also show through rigorous evaluation that they are effective. A major focus in IR is IR
mechanisms’ capability of ranking relevant documents optimally for the users, given a query. Searching for information in
practice involves searchers, however, and is highly interactive. When human searchers have been incorporated in evaluation
studies, the results have often suggested that better ranking does not necessarily lead to better search task, or work task,
performance. Therefore, it is not clear which system or interface features should be developed to improve the effectiveness
of human task performance. In the present article, we focus on the evaluation of task-based information interaction (TBII).
We give special emphasis to learning tasks to discuss TBII in more concrete terms. Information interaction is here understood
as behavioral and cognitive activities related to task planning, searching information items, selecting between them, working
with them, and synthesizing and reporting. These five generic activities contribute to task performance and outcome and can
be supported by information systems. In an attempt toward task-based evaluation, we introduce program theory as the evaluation
framework. Such evaluation can investigate whether a program consisting of TBII activities and tools works and how it works
and, further, provides a causal description of program (in)effectiveness. Our goal in the present article is to structure
TBII on the basis of the five generic activities and consider the evaluation of each activity using the program theory framework.
Finally, we combine these activity-based program theories in an overall evaluation framework for TBII. Such an evaluation
is complex due to the large number of factors affecting information interaction. Instead of presenting tested program theories,
we illustrate how the evaluation of TBII should be accomplished using the program theory framework in the evaluation of systems
and behaviors, and their interactions, comprehensively in context.