Mohsen Tavakol

Making sense of Cronbach's alpha

Medical educators attempt to create reliable and valid tests and questionnaires in order to enhance the accuracy of their assessment and evaluations. Validity and reliability are two fundamental elements in the evaluation of a measurement instrument. Instruments can be conventional knowledge, skill or attitude tests, clinical simulations or survey questionnaires. Instruments can measure concepts, psychomotor skills or affective values. Validity is concerned with the extent to which an instrument measures what it is intended to measure. Reliability is concerned with the ability of an instrument to measure consistently.1 It should be noted that the reliability of an instrument is closely associated with its validity. An instrument cannot be valid unless it is reliable. However, the reliability of an instrument does not depend on its validity.2 It is possible to objectively measure the reliability of an instrument and in this paper we explain the meaning of Cronbach’s alpha, the most widely used objective measure of reliability. Calculating alpha has become common practice in medical education research when multiple-item measures of a concept or construct are employed. This is because it is easier to use in comparison to other estimates (e.g. test-retest reliability estimates)3 as it only requires one test administration. However, in spite of the widespread use of alpha in the literature the meaning, proper use and interpretation of alpha is not clearly understood. 2, 4, 5 We feel it is important, therefore, to further explain the underlying assumptions behind alpha in order to promote its more effective use. It should be emphasised that the purpose of this brief overview is just to focus on Cronbach’s alpha as an index of reliability. Alternative methods of measuring reliability based on other psychometric methods, such as generalisability theory or item-response theory, can be used for monitoring and improving the quality of OSCE examinations 6-10, but will not be discussed here. What is Cronbach alpha? Alpha was developed by Lee Cronbach in 195111 to provide a measure of the internal consistency of a test or scale; it is expressed as a number between 0 and 1. Internal consistency describes the extent to which all the items in a test measure the same concept or construct and hence it is connected to the inter-relatedness of the items within the test. Internal consistency should be determined before a test can be employed for research or examination purposes to ensure validity. In addition, reliability estimates show the amount of measurement error in a test. Put simply, this interpretation of reliability is the correlation of test with itself. Squaring this correlation and subtracting from 1.00 produces the index of measurement error. For example, if a test has a reliability of 0.80, there is 0.36 error variance (random error) in the scores (0.80×0.80 = 0.64; 1.00 – 0.64 = 0.36).12 As the estimate of reliability increases, the fraction of a test score that is attributable to error will decrease.2 It is of note that the reliability of a test reveals the effect of measurement error on the observed score of a student cohort rather than on an individual student. To calculate the effect of measurement error on the observed score of an individual student, the standard error of measurement must be calculated (SEM).13 If the items in a test are correlated to each other, the value of alpha is increased. However, a high coefficient alpha does not always mean a high degree of internal consistency. This is because alpha is also affected by the length of the test. If the test length is too short, the value of alpha is reduced.2, 14 Thus, to increase alpha, more related items testing the same concept should be added to the test. It is also important to note that alpha is a property of the scores on a test from a specific sample of testees. Therefore investigators should not rely on published alpha estimates and should measure alpha each time the test is administered.14 Use of Cronbach’s alpha Improper use of alpha can lead to situations in which either a test or scale is wrongly discarded or the test is criticised for not generating trustworthy results. To avoid this situation an understanding of the associated concepts of internal consistency, homogeneity or unidimensionality can help to improve the use of alpha. Internal consistency is concerned with the interrelatedness of a sample of test items, whereas homogeneity refers to unidimensionality. A measure is said to be unidimensional if its items measure a single latent trait or construct. Internal consistency is a necessary but not sufficient condition for measuring homogeneity or unidimensionality in a sample of test items. 5, 15 Fundamentally, the concept of reliability assumes that unidimensionality exists in a sample of test items16 and if this assumption is violated it does cause a major underestimate of reliability. It has been well documented that a multidimensional test does not necessary have a lower alpha than a unidimensional test. Thus a more rigorous view of alpha is that it cannot simply be interpreted as an index for the internal consistency of a test. 5, 15, 17 Factor Analysis can be used to identify the dimensions of a test.18 Other reliable techniques have been used and we encourage the reader to consult the paper “Applied Dimensionality and Test Structure Assessment with the START-M Mathematics Test” and to compare methods for assessing the dimensionality and underlying structure of a test.19 Alpha, therefore, does not simply measure the unidimensionality of a set of items, but can be used to confirm whether or not a sample of items is actually unidimensional.5 On the other hand if a test has more than one concept or construct, it may not make sense to report alpha for the test as a whole as the larger number of questions will inevitable inflate the value of alpha. In principle therefore, alpha should be calculated for each of the concepts rather than for the entire test or scale. 2, 3 The implication for a summative examination containing heterogeneous, case-based questions is that alpha should be calculated for each case. More importantly, alpha is grounded in the ‘tau equivalent model’ which assumes that each test item measures the same latent trait on the same scale. Therefore, if multiple factors/traits underlie the items on a scale, as revealed by Factor Analysis, this assumption is violated and alpha underestimates the reliability of the test.17 If the number of test items is too small it will also violate the assumption of tau-equivalence and will underestimate reliability.20 When test items meet the assumptions of the tau-equivalent model, alpha approaches a better estimate of reliability. In practice, Cronbach’s alpha is a lower-bound estimate of reliability because heterogeneous test items would violate the assumptions of the tau-equivalent model.5 If the calculation of “standardised item alpha” in SPSS is higher than “Cronbach’s alpha”, a further examination of the tau-equivalent measurement in the data may be essential. Numerical values of alpha As pointed out earlier, the number of test items, item inter-relatedness and dimensionality affect the value of alpha.5 There are different reports about the acceptable values of alpha, ranging from 0.70 to 0.95. 2, 21, 22 A low value of alpha could be due to a low number of questions, poor inter-relatedness between items or heterogeneous constructs. For example if a low alpha is due to poor correlation between items then some should be revised or discarded. The easiest method to find them is to compute the correlation of each test item with the total score test; items with low correlations (approaching zero) are deleted. If alpha is too high it may suggest that some items are redundant as they are testing the same question but in a different guise. A maximum alpha value of 0.90 has been recommended.14 Summary High quality tests are important to evaluate the reliability of data supplied in an examination or a research study. Alpha is a commonly employed index of test reliability. Alpha is affected by the test length and dimensionality. Alpha as an index of reliability should follow the assumptions of the essentially tau-equivalent approach. A low alpha appears if these assumptions are not meet. Alpha does not simply measure test homogeneity or unidimensionality as test reliability is a function of test length. A longer test increases the reliability of a test regardless of whether the test is homogenous or not. A high value of alpha (> 0.90) may suggest redundancies and show that the test length should be shortened.

Assessing the skills of surgical residents using simulation.

Much is still to be learned about the assessment of simulation-based surgical skills training. However, assessing surgery skills through simulation is a new horizon in medical education. Providing a safe environment for surgical residents to assess their performance rigorously without placing patients in jeopardy is valuable. Using simulators (both warm and cold) as a means to assess trainees has been established. However, also problems concerning the validity and reliability of such simulation-based assessment tools exist, particularly in surgery, that may need to be investigated even more to decide whether to use them as a tool for assessing the performance of surgical residents.

Grounded Theory in Medical Education Research

Abstract The grounded theory method provides a systematic way to generate theoretical constructs or concepts that illuminate psychosocial processes common to individual who have a similar experience of the phenomenon under investigation. There has been an increase in the number of published research reports that use the grounded theory method. However, there has been less medical education research, which is based on the grounded theory tradition. The purpose of this paper is to introduce basic tenants of qualitative research paradigm with specific reference to ground theory. The paper aims to encourage readers to think how they might possibly use the grounded theory method in medical education research and to apply such a method to their own areas of interest. The important features of a grounded theory as well as its implications for medical education research are explored. Data collection and analysis are also discussed. It seems to be reasonable to incorporate knowledge of this kind in medical education research.

Empathy in Iranian medical students: A preliminary psychometric analysis and differences by gender and year of medical school

Background: It has been well documented that effective empathic communication in the context of patient care is associated with improved health care outcomes. However, the emphasis given to empathy in medical education in Iran is limited, and the state of such teaching is unknown in many countries. Aims: To determine the psychometric properties of an Iranian translation of the Jefferson Scale of Physician Empathy (JSPE) among medical students, and to examine the differences on mean empathy scores by gender and the different years of medical school. Method: A cross-sectional study was conducted among medical students. Data analysis was based on 181 questionnaires. Principal component analysis (PCA) with Varimax rotation was used to identify the number and composition of components constituting the developed constructs. Results: The PCA yielded three factors: Compassionate care, perspective–taking, and the ability to walk in the patients shoes. No statistically significant differences in the empathy means scores were found by gender and the different years of medical school. Conclusions: The Persian version of JSPE is a psychometrically sound instrument to measure empathy. Cultural backgrounds and pedagogical practice may influence medical students’ attitudes towards empathy. Some recommendations are made, and the study limitations are discussed.

Psychometric properties and confirmatory factor analysis of the Jefferson Scale of Physician Empathy

BackgroundEmpathy towards patients is considered to be associated with improved health outcomes. Many scales have been developed to measure empathy in health care professionals and students. The Jefferson Scale of Physician Empathy (JSPE) has been widely used. This study was designed to examine the psychometric properties and the theoretical structure of the JSPE.MethodsA total of 853 medical students responded to the JSPE questionnaire. A hypothetical model was evaluated by structural equation modelling to determine the adequacy of goodness-of-fit to sample data.ResultsThe model showed excellent goodness-of-fit. Further analysis showed that the hypothesised three-factor model of the JSPE structure fits well across the gender differences of medical students.ConclusionsThe results supported scale multi-dimensionality. The 20 item JSPE provides a valid and reliable scale to measure empathy among not only undergraduate and graduate medical education programmes, but also practising doctors. The limitations of the study are discussed and some recommendations are made for future practice.

Post-examination analysis of objective tests

One of the key goals of assessment in medical education is the minimisation of all errors influencing a test in order to produce an observed score which approaches a learners ‘true’ score, as reliably and validly as possible. In order to achieve this, assessors need to be aware of the potential biases that can influence all components of the assessment cycle from question creation to the interpretation of exam scores. This Guide describes and explains the processes whereby objective examination results can be analysed to improve the validity and reliability of assessments in medical education. We cover the interpretation of measures of central tendency, measures of variability and standard scores. We describe how to calculate the item-difficulty index and item-discrimination index in examination tests using different statistical procedures. This is followed by an overview of reliability estimates. The post-examination analytical methods described in this guide enable medical educators to construct reliable and valid achievement tests. They also enable medical educators to develop question banks using the collection of appropriate questions from existing examination tests in order to use computerised adaptive testing.

Quantitative and qualitative methods in medical education research: AMEE Guide No 90: Part II

Abstract Medical educators need to understand and conduct medical education research in order to make informed decisions based on the best evidence, rather than rely on their own hunches. The purpose of this Guide is to provide medical educators, especially those who are new to medical education research, with a basic understanding of how quantitative and qualitative methods contribute to the medical education evidence base through their different inquiry approaches and also how to select the most appropriate inquiry approach to answer their research questions.

Medical students’ understanding of empathy: a phenomenological study

Medical Education 2012: 46: 306–316

Are Asian International Medical Students Just Rote Learners

A wide variety of countries are seeking to attract international medical students. This could be due to the fact that their universities not only receive the economic benefit from these students, but also because they recognise the issues of cultural diversity and pedagogical practice. This review paper draws on literature to understand more fully the learning process of Asian international students. Whereas views on learning are different across cultures, medical school teachers must understand how Asian international students learn based on their culture. Two general themes emerged from the literature review: firstly culture’s influence on learning and secondly memorisation versus understanding, both of which relate to the learning process of Asian international students. This study shows that Asian international students have a different approach to learning, which is not just about rote learning. Changes in attitudes towards Asian international students may stimulate the internationalisation of a more culturally sensitive form of medical education. The paper suggests further work on the area of appreciative thinking in order to identify the epistemological and ontological dimensions for a flexible approach to learning.

Medical Education in Iran: An Exploration of Some Curriculum Issues

Abstract Background: Although Iran is a large and populous country, the state of medical education is poorly understood and under researched. However, it is apparent that, in recent years, calls for reform in medical education have not tended to lead to major changes. As a result, the curricula used are in danger of being perceived as dated and less effective than they should be. Purpose: This exploratory study is designed to investigate the perspectives and experiences of a group of the most influential medical education course planners in Iran. Its aim is to investigate their views about the nature of the undergraduate medical curriculum in Iran and explore with them ways in which such curricula could be modernized and improved. Methods: In-depth, semi-structured interviews were used to explore the perceptions of an elite group of medical education course planners who all work in prestigious universities in Tehran. Each of these 10 individuals was interviewed twice, over a period of several months, in order that an in-depth view of their perceptions could be unraveled. Results: A deep concern about the lack of an innovative medical education curriculum in Iran emerged as the strongest theme from the interviews. There is widespread agreement that the current curriculum is too oriented towards the students passively learning facts. There is also a perceived lack of integration between the two-year basic science courses and clinical learning. Furthermore, participants feel that poor teaching facilities and overcrowding of students has provided an unsuitable learning environment. Both positive and negative attitudes toward educational strategies in curriculum development were demonstrated. Some of the barriers to curriculum change were also discussed. Conclusions: There is a real need for major changes in the medical education curriculum in Iran. The results of this study suggest that a move towards a curriculum that engages students as active participants in a process of lifelong learning would be highly beneficial. As clinically qualified doctors they will face many challenges in the years ahead, and a modernized curriculum should help them to acquire the necessary knowledge and develop the clinical skills and problem solving abilities they will need.