Research Assistant Z is particularly enthusiastic when working with subjects who are receiving SUPER treatment, but less animated when working with subjects who are receiving a placebo. Z's actions may introduce what type of internal invalidity into the research on SUPER treatment?

Treatment misidentification

Explanation:

Assistant Z's action introduces treatment misidentification during his therapy. It arises when the researcher claims a change in independent variable due to the dependent variable. Placebo effect is a way of treatment when patients are provided with fake pills.

However, it is due to a treatment that goes unnoticed by the researcher during the treatment which is closely related to the primary treatment. The researcher unconsciously distorts the result when working with patients. Thus, the researcher introduces internal invalidity due to treatment misidentification.  

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answer; pluralist democracy;