Active learning can be achieved by introducing students' activity into the traditional lecture sessions. , highlighted the use of one such approach called the concept tests (or "Concepts Tests") method in their Unified Engineering class. In this method lectures are punctuated by brief, multiple-choice conceptual questions to test students' understanding of the material. When most students do well on a question, the lecture proceeds to new material. However, when the concept test reveals that students have conceptual problems or misunderstandings, students are encouraged to work in small groups to work out the answer to the question. When students were asked to compare the active learning techniques to the traditional lecture format, their responses reflected an overall positive attitude towards the active learning techniques. Specifically, some students commented on the effect of the active learning techniques on improving their learning and understanding of the content, and in stimulating their thinking and classroom participation. Another important component of active learning highlighted by  is the type of activity, which influences how much classroom material is retained. It is essential that activities promote thoughtful engagement on the part of the students and are designed around important learning outcomes. The importance of students' engagement is widely accepted and there is considerable evidence to support the effectiveness of students' engagement on a broad range of learning outcomes.  reports that one of the most important predictors of success in college is students' involvement. He examined the performance of over 90 students in five chemical engineering courses and found significantly improved performance for students in classes with extensive use of active and cooperative learning techniques as opposed to students in a traditionally taught group. The experimental group outperformed the comparison group on a number of measures, including retention and graduation in chemical engineering, and many more of the graduates in this group chose to pursue advanced study in the field.