H

Halo Effect
Bias created by an observer's tendency to rate, perhaps unintentionally, certain objects or persons in a manner that reflects what was previously anticipated.

Hawthorne Effect
A tendency of research subjects to act atypically as a result of their awareness of being studied, as opposed to any actual treatment that has occurred. FOR EXAMPLE, if a school principal observes a classroom of students reacting politely and enthusiastically to a new student teacher, such behavior could be a result of the principal's presence in the classroom, as opposed to the quality of the student teacher.

Histogram
A graphic depiction of the distribution of a variable.

History Effect
This threat to internal validity refers to specific events, other than the program, which may have taken place during the course of study which may have produced the results. FOR EXAMPLE, a highly publicized trial involving local law enforcement which occurs during the time of program operation may impact community attitudes.

Hypothesis
A specific statement regarding the relationship between two variables. In evaluation research, this typically involves a prediction that the program or treatment will cause a specified outcome. Hypotheses are confirmed or denied based on empirical analysis.