Controlled experiments and comparison tests are similar in design and practice. We will discuss their design together, but first we review the differences between the two:
Controlled experiments need to create results from at least two conditions. Comparison tests generate results from at least two products. For both kinds of studies, the practitioner designs the study to ensure that the situations (e.g. tasks, environment, participants, instructions) are the same (or at least comparable) among the different conditions or products.
In contrast, the observational study does not have controlled conditions. For this kind of study, the practitioner selects situations or products, observes their usage and compares their results.