Abstract: Studied the heuristic factors in choosing positive diagnostic and negative diagnostic Test. 592 Xinhai Conservatory of Music students participated in 4 experiments. Experiment 1 tests the tendency on choosing positive, negative, diagnostic and nondiagnostic questions. Experiment 2 focus the same tendency on double optional questions. Experiment 3 explores the improvement of negative diagnostic test when offer the falsify sample. Experiment 4 researches the same improvement when the difficulty of positive test is enhanced. The results show that (1) participants are significantly more likely to prefer positive tests over negative tests, and prefer diagnostic tests over nondiagnostic test. (2)participants are tended to choose negative tests question between the positive nondiagnostic and negative diagnostic test question. (3)offering falsify sample or enhancing positive test complexity promotes negative diagnostic test. The result consisted with the predicting by mental model theory. A conversion-mechanism provides a complemented explanation for the model theory.

Key words: selection task, mental model, heuristic factors, conversion-mechanism