Final answer:
The primary disadvantage of disguised research is that people might change their behavior if they realize they are being observed. This could alter the validity of the research findings due to observer bias or the Hawthorne effect.
Step-by-step explanation:
A primary disadvantage of disguised research is d. people will change their behavior. This type of research implies that the subjects are unaware they are being studied, which is meant to prevent them from changing their behavior due to the awareness of observation—known as the Hawthorne effect. However, in disguised research, if people discover they are being studied without their knowledge, they may feel deceived and their behavior might change as a result. Moreover, ethical guidelines often require informed consent, which cannot be obtained in disguised research.
In contrast, secondary data or nonreactive research, where researchers use existing data, does not involve direct interaction with subjects and thus doesn't risk altering their behavior. This is often seen as an advantage in terms of research validity. Another key issue with disguised research is observer bias, where researchers may unintentionally influence their observations to fit preconceived hypotheses. To combat this, criteria for behavior should be established beforehand and inter-rater reliability can be used to assess the consistency of observations by different researchers.