There are numerous definitions of critical thinking, but the core concept has been said to be careful, reasoned, goal-directed thinking. There are also many conceptualizations of critical thinking, which are generally more detailed than brief definitions, and there are different views about what the goal(s) of critical thinking instruction should be. Whether critical thinking is a good thing is a matter of debate. Approaches to teaching critical thinking vary, partly according to whether they focus on general principles of critical thinking or on subject-matter content or on a combination of both. A meta-analysis research report published in 2015 concluded that, subject to certain qualifications, a variety of critical thinking skills and dispositions can develop in students through instruction at all educational levels. Critical thinking instruction has been influenced by research in cognitive psychology that has suggested strategies for countering factors (e.g., biases) that the research has found to produce irrational beliefs. Methods of assessing critical thinking ability include teacher-designed tests and standardized tests. A research report published in 2014 on assessing critical thinking in higher education describes challenges involved in designing standardized critical thinking tests and proposes a framework for a “next-generation” assessment. The challenges include achieving a balance between the assessment's real-world relevance and its psychometric quality, and designing an assessment useful for instructional purposes and for comparisons of programs and institutions. The proposed framework is based partly on a review of existing frameworks of critical thinking in higher education. It has two analytical dimensions and two synthetic dimensions, and a dimension on understanding causation and explanation. Surveys show that employers value employees with strong critical thinking ability; this fact has significant implications for students, teachers, and administrators at all levels of education.