Previous research studies show that interacting elements affecting reported classroom observation of teacher behavior are: (1) teacher characteristics; (2) observer characteristics; (3) influence of status characteristics upon social interaction; (4) effect of sex and topic on judgment of competence; (5) beliefs concerning teaching and teaching research held by the observer; (6) effects of observer preconceptions and personal biases; (7) effects of environmental conditions, physical condition of the observer, judgment habits, and level of difficulty of the experiment; (8) effects of time constraint on observational situations; (9) observer expectations; (10) self concept of observer; (11) observer opinions and attitudes; and (12) characteristics of instruments used in coding observed teacher behavior. A list of thirty-three characteristics of observers who may act as raters for educational research is provided to explain rater behavior. The operation of bias in the coding process which may be due to elements other than the situation and the instrument used is described. (JD)