Increased motivation by teacher have been found to increase marks of students in examination. This bias is called:-

Pygmalion Bias - Increased Motivation by teacher have been found to increase marks of Student in Examination. This is type of "Investigatory Selection Bias". Hawthorne Bias - Study Subject change their behaviour during study , so outcome is changed. It is seen in Coho study. Berksonian Bias - Occurs due to different rates of Hospital Admission. This is type of Selection Investigation Bias. Golem bias - Demotivation by teachers can decrease marks of students.