Teaching Critical Thinking: The More, the Better!

A three-group study (N = 75) examined the question whether different amounts of critical thinking instruction would lead to significantly different levels of improvement in critical thinking test scores. The researcher used the Cornell Z Test (Ennis, Millman, & Tomko, 1985) to compare the pre and post scores of critical thinking (full-treatment), psychology (partial-treatment), and rhetoric (no treatment) student groups.A one-way ANOVA revealed a significant difference among the groups at post testing. Subsequent Newman-Keuts analysis indicated significant differences in all three pairwise comparisons. In other words, the partial treatment psychology group improved measurably more than the no-treatment rhetoric student controls, and the full-treatment critical thinking students significantly outperformed both of the other groups. The overall effect size was large, and the observed power was correspondingly high. Additional controls helped to address many of the commonly recognized threats to validity in quasi-experimental research. Introduction Critical thinking courses, often packaged and marketed as basic logic courses, have long been a feature of the American higher education scene. More recently, with the advent of the critical thinking across the curriculum movement (Cameron & Richmond, 2002), numerous catalog course descriptions and syllabi have come to reflect the strategic infusion of small to moderate amounts of critical thinking materials into a fairly broad spectrum of undergraduate offerings in a wide variety of academic disciplines. An obvious assumption underlying both pedagogical procedures is the claim that they do in fact produce improved critical thinking. But what epistemic or empirical justification do such assertions have? Does it really make any measurable difference which of the two approaches to critical thinking instruction one uses? For that matter, how does one know whether any extent of critical thinking intervention has a quantitatively notable effect? Even more fundamental, what component attributes are to be included in a defensible construct of "critical thinking," and how is it to be adequately implemented? The following paper attempts to address these and other related issues. It reports the results of a controlled study of critical thinking development in a sample (N = 75) of community college students. A full-treatment experimental group was taking a critical thinking course. Another partial-treatment experimental group was enrolled in an introductory psychology course (i.e., the infusion technique). A third no-treatment control group was composed of rhetoric students. The critical thinking group had more than 40 hours of classroom instruction in critical thinking and over 80 hours of homework exercises. The psychology group received approximately 10 hours of class time intervention and about 20 hours of additional outside assignments. The rhetoric group, by way of contrast, had little or no critical thinking instruction (as operationally defined herein). The investigation focused on a specific research question: Would a full-treatment group of critical thinking students improve their Cornell Z scores significantly more than both a partial-treatment group of psychology students and a no-treatment group of rhetoric student controls? The study is a sequel to Solon (2001). The construct of critical thinking A survey of the literature indicates that the term "critical thinking" is employed in a variety of ways. Some writers, such as McPeck (1981), use it exclusively in reference to those discipline specific analytical and problem solving skills necessary for a fairly advanced level of work in a particular field. There is, however, a much more commonly accepted sense of the term, and that is the intent here. "Critical thinking," as used in this paper, refers to a set of basic and generic reasoning skills. These skills include the ability to identify and/or distinguish between: 1. …