In a Study Designed to Assess the Effectiveness of a New

In a study designed to assess the effectiveness of a new therapeutic technique to help patients stop smoking, research participants are asked to record in a diary each time they smoke a cigarette. At the beginning of the two week experiment participants are very careful about noting every time they smoke a cigarette. However by the end of the two weeks they often forget to record each cigarette they smoke making it appear that they smoked less at the end of the experimental treatment. The results in this study are confounded by

A) instrumentation.
B) attrition.
C) history.
D) maturation.