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Within-subject Design

With a within-subject design, a major problem is that once a subject has completed the first part of the study, the experience or changed circumstances could influence performance in later parts of the study. This problem is known as a SEQUENCE or ORDER effect.

1. The Problem of Controlling Sequence Effects -- COUNTERBALANCING.

a. Testing once per condition (Incomplete design) -- participants are tested in each of the conditions, but only once per condition.

b. Testing more than once per condition (Complete design)

2.  Problems with Biasing

a. Experimenter bias -- biased experimenters might treat the research participants in the various conditions differently.

b. Controlling for experimenter bias standardized (mechanized) procedures; double-blind design.

c. Participant bias

3. Controlling for participant bias deception; manipulation check; field research