advantages and disadvantages of cronbach alpha

In other words, the higher the \( \alpha \) coefficient, the more the items have shared covariance and probably measure the same underlying concept. doi: 10.1177/1094428114555994, Cortina, J. In other words, the reliability of any given measurement refers to the extent to which it is a consistent measure of a concept, and Cronbachs alpha is one way of measuring the strength of that consistency. Methodol. Both GLB and GLBa present a positive bias under normality, however GLBa shows approximatively less % bias than GLB (see Table 1). There are many ways of calculating Cronbachs alpha in R using a variety of different packages. Adv Health Sci Educ Theory Pract. One of the big problems in this country is that we dont give everyone an equal chance. Development of the idea of research and theoretical framework (IT, JA). This requires that other indices of internal consistency be reported along with alpha coefficient, and that when a scale is composed of large number of items, factor analysis should be performed, and appropriate internal consistency estimation method applied. Iramaneerat C, Yudkowsky R, Myford CM, Downing S. Quality control of an OSCE using generalizability theory and many-faceted Rasch measurement. Considering the coefficients defined above, and the biases and limitations of each, the object of this work is to evaluate the robustness of these coefficients in the presence of asymmetrical items, considering also the assumption of tau-equivalence and the sample size. And, in addition, you can address construct validity by examining whether or not there exist empirical relationships between your measure of the underlying concept of interest and other concepts to which it should be theoretically related. Validity: establishing meaning for assessment data through scientific evidence. 74, 7481. Bias of coefficient alpha for fixed congeneric measures with correlated errors. The general rule of thumb is that a Cronbach's alpha of .70 and above is good, .80 and above is better, and .90 and above is best. Lower bounds for the reliability of the total score on a test composed of non-homogeneous items: II: a search procedure to locate the greatest lower bound. We have gone too far in pushing equal rights in this country. PubMed Central In internal consistency reliability estimation we use our single measurement instrument administered to a group of people on one occasion to estimate reliability. doi: 10.1080/00273171.2012.715555, Revelle, W. (2015a). CM DART, University Veterinary Centre, Department of Veterinary Clinical Sciences, The University of Sydney, Werombi Road, Camden, New South Wales 2570. Development of the R language syntax (IT, JA). The results of this study are stimulating and should encourage other clinical departments at Dammam University to use the OSCE in the future. The authors declare that they have no competing interests. Cronbach's alpha is a statistical measure. This was the result of faculty misunderstanding because it was a first time experience.Footnote 3 This issue was managed with feedback after each exam to avoid these mistakes in future exams. Cronbach's alpha and more. This is because the two observations are related over time the closer in time we get the more similar the factors that contribute to error. The present study investigated how ethical ideologies influenced attitude toward animals among undergraduate students. The Cronbachs alphas for the stations ranged from 0.5 to 0.9. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Pearsons correlation was 0.63, which demonstrates that the OSCE is a valid exam. Although the standards for what makes a good \( \alpha \) coefficient are entirely arbitrary and depend on your theoretical knowledge of the scale in question, many methodologists recommend a minimum \( \alpha \) coefficient between 0.65 and 0.8 (or higher in many cases); \( \alpha \) coefficients that are less than 0.5 are usually unacceptable, especially for scales purporting to be unidimensional (but see Section III for more on dimensionality). Lawson D. Applying generalizability theory to high-stakes objective structured clinical examinations in a naturalistic environment. doi: 10.1007/BF02295980, Yang, Y., and Green, S. B. Data analysis and interpretation of data (IT, JA). Received: 22 September 2015; Accepted: 09 May 2016; Published: 26 May 2016. Plasma noradrenaline and renin concentrations are reduced. No single reliability index can be considered as a perfect tool for assessing the OSCE. To measure the validity of the exam, we conducted a Pearsons correlation to compare the results of the OSCE and written exam scores. You can use alpha to test the inter-item reliability of the variables that make up each factor you discover. doi: 10.5093/ejpalc2014a4. On the other hand, in some studies it is reasonable to do both to help establish the reliability of the raters or observers. \( k \) refers to the number of scale items, \( \sigma_{y_{i}}^{2} \) refers to the variance associated with item i, \( \sigma_{x}^{2} \) refers to the variance associated with the observed total scores, \( \bar{c} \) refers to the average of all covariances between items, \( \bar{v} \) refers to the average variance of each item. 15, 2335. and specifically for men. The asymptotic bias of minimum trace factor analysis, with applications to the greatest lower bound to reliability. Hesitancy toward the COVID-19 vaccine has hindered its rapid uptake among the Hispanic and Latinx populations. The average inter-item correlation uses all of the items on our instrument that are designed to measure the same construct. Analysis of quality and feasibility of an objective structured clinical examination (OSCE) in preclinical dental education. For legal and data protection questions, please refer to our Terms and Conditions and Privacy Policy. The major difference is that parallel forms are constructed so that the two forms can be used independent of each other and considered equivalent measures. The other major way to estimate inter-rater reliability is appropriate when the measure is a continuous one. II. This increase occurred over a short period as a first experience for the department of internal medicine. *Correspondence: Italo Trizano-Hermosilla, italo.trizano@ufrontera.cl, http://ftp.daum.net/CRAN/web/packages/GPArotation/GPArotation.pdf, https://www.webmedcentral.com/wmcpdf/Article_WMC001649.pdf, http://personality-project.org/r/psych/help/glb.algebraic.html, http://personality-project.org/r/html/guttman.html, http://www.crame.ualberta.ca/docs/April 2012/AERA paper_2012.pdf, Creative Commons Attribution License (CC BY). As a result, this may have produced a misleading value that is not as reliable, and this is the main disadvantage of Cronbachs alpha (Table1) [3, 5, 13]. 2. Assessment of reliability when test items are not essentially t-equivalent. In effect we judge the reliability of the instrument by estimating how well the items that reflect the same construct yield similar results. A topic that has attracted particular attention in the psychometric literature is Cronbach's alpha (Cronbach, doi: 10.1007/s11336-003-0974-7, Zinbarg, R. E., Yovel, I., Revelle, W., and McDonald, R. (2006). The Aggregate procedure is used to compute the pieces of the KR21 formula and save them in a new data set, (kr21_info). Educ Psychol Measur. Available online at: https://www.webmedcentral.com/wmcpdf/Article_WMC001649.pdf, Lila, M., Oliver, A., Catal-Miana, A., Galiana, L., and Gracia, E. (2014). Psychometric properties Reliability. OK, its a crude measure, but it does give an idea of how much agreement exists, and it works no matter how many categories are used for each observation. https://doi.org/10.1186/s13104-015-1533-x, DOI: https://doi.org/10.1186/s13104-015-1533-x. Psychol. As stated by Sijtsma (2009), its popularity is such that Cronbach (1951) has been cited as a reference more frequently than the article on the discovery of the DNA double helix. The blue print for each exam was established. Higher values indicate higher agreement . The R2 coefficient is affected if there is faculty misunderstanding of the difference between the checklist and global rating. The second study was the first to discuss the effect of exam duration on the reliability index of the OSCE and reported on the effect of different days of the exam on its validity [7, 15, 16]. . 66, 930944. Effect of Varying Sample Size in Estimation of Coefficients of Internal Consistency. On the use, the misuse, and the very limited usefulness of Cronbach's alpha. The OSCE scores for the students were between 18.7 and 36.9, with a mean of 27.6, a median of 27.9, a standard deviation (SD) of 4.07, a skewness of 0.07 (which is almost 0),and a normal distribution, where the definition of skewness is described as asymmetry from the normal distribution in a set of statistical data. If your measurement consists of categories the raters are checking off which category each observation falls in you can calculate the percent of agreement between the raters. McDonald (1999) proposed the t coefficient for estimating reliability from a factorial analysis framework, which can be expressed formally as: Where j is the loading of item j, j2 is the communality of item j and equates to the uniqueness. Advantages and disadvantages of alpha 2-adrenoceptor agonists for systemic hypertension Alpha 2-receptor agonists are effective antihypertensive drugs that reduce sympathetic activity by both central and peripheral mechanisms. Cronbach's alpha: The most commonly used measurement of internal consistency. There are several actions that could trigger this block including submitting a certain word or phrase, a SQL command or malformed data. https://doi.org/10.1186/s13104-015-1533-x, http://creativecommons.org/licenses/by/4.0/, http://creativecommons.org/publicdomain/zero/1.0/. Psychometrika 74, 155167. Cronbach's alpha, a measure of internal consistency, was calculated to test the reliability of the questionnaire. After each exam, the coordinator of the course met with faculty and students to assess and correct any problems with the OSCE to ensure better reliability in the future and they were confidents with OSCE. This study demonstrated improvement in conducting the OSCE through experience, which was reflected by the increase in the reliability indexes after each exam. Disadvantages: susceptible to the threat of selection differences. J Pers Asses. Int J Med Educ. In the example, we find an average inter-item correlation of .90 with the individual correlations ranging from .84 to .95. However, the encouraging point is that the differences between the R2 values were very small. Downing SM. Sheng and Sheng (2012) observed recently that when the distributions are skewed and/or leptokurtic, a negative bias is produced when the coefficient is calculated; similar results were presented by Green and Yang (2009b) in an analysis of the effects of non-normal distributions in estimating reliability. 3. to Zeus and so onand then they turned to drinking Pausanias broke the silence by. Finally, the item option will produce a table displaying the number of non-missing observations for each item, the correlation of each item with the summed index (item-test correlations), the correlation of each item with the summed index with that item excluded (item-rest correlations), the covariance between items and the summed index, and what the \( \alpha \) coefficient for the scale would be were each item to be excluded. All authors read and approved the final manuscript. For more information, please visit our Permissions help page. This indicated that students were performing better than expected and that the exam was a good stimulator for reading. Fully-functional online survey tool with various question types, logic, randomisation, and reporting for unlimited number of responses and surveys. For example, lets consider the six scale items from the American National Election Study (ANES) that purport to measure equalitarianismor an individuals predisposition toward egalitarianismall of which were measured using a five-point scale ranging from agree strongly to disagree strongly: After accounting for the reversely-worded items, this scale has a reasonably strong \( \alpha \) coefficient of 0.67 based on responses during the 2008 wave of the ANES data collection. the main problem with this approach is that you dont have any information about reliability until you collect the posttest and, if the reliability estimate is low, youre pretty much sunk. 2010;32:80211. Cronbachs alpha is not a measure of dimensionality, nor a test of unidimensionality. Res. doi:10.1111/j.1600-0579.2010.00653.x. Other authors, such as Revelle and Zinbarg (2009) and Green and Yang (2009a), recommend the use of , however this coefficient only produced good results in the condition of normality, or with low proportion of skewness items. If we use Form A for the pretest and Form B for the posttest, we minimize that problem. Because we measured all of our sample on each of the six items, all we have to do is have the computer analysis do the random subsets of items and compute the resulting correlations. Importantly, although the exam occurred on different days, this did not change the validity of the exam, a result that few studies have reported. Spearmans rank correlation was stable in the first and second group and increased slightly with the third group, with a slight decrease in the R2 coefficient in the last group after a slight increase in the second group (Table1). Provided by the Springer Nature SharedIt content-sharing initiative. According to Revelle (2015a) this procedure adopts the form which is most faithful to the original definition by Jackson and Agunwamba (1977), and it has the added advantage of introducing a vector to weight the items by importance (Al-Homidan, 2008). Finally, a factor analysis was used to assess exam homogeneity. Type help alpha in Statas command line for more options. In addition, the limitations and strengths of several recommendations . Advantages of a Bogardus Social Distance Scale Some advantages of the Bogardus social distance scale are: Ease of use: The scale is very easy to create and administer. Dev. For example, Micceri (1989) estimated that about 2/3 of ability and over 4/5 of psychometric measures exhibited at least moderate asymmetry (i.e., skewness around 1). Res. Additionally, it is worth to conclude the validity Arthritis 2014:385256. doi: 10.1155/2014/385256, Woodhouse, B., and Jackson, P. H. (1977). Skewed items: Standard normal Xij were transformed to generate non-normal distributions using the procedure proposed by Headrick (2002) applying fifth order polynomial transforms: The coefficients implemented by Sheng and Sheng (2012) were used to obtain centered, asymmetrical distributions (asymmetry 1): c0 = 0.446924, c1 = 1.242521, c2 = 0.500764, c3 = 0.184710, c4 = 0.017947, c5 = 0.003159. J. Psychoeduc. University of Dammam, Prince Saud bin Fahd Street, PO Box 3669, Khobar, 31952, Saudi Arabia, University of Dammam, PO Box 2435, Dammam, 31451, Saudi Arabia, Mona H. Al-Sheikh,Mohannad A. Al-Ghamdi,Abdulaziz M. Al-Hawas,Abdullah S. Al-Bahussain&Ahmed A. Al-Dajani, You can also search for this author in Meas. If all of the scale items are entirely independent from one another (i.e., are not correlated or share no covariance), then \( \alpha \) = 0; and, if all of the items have high covariances, then \( \alpha \) will approach 1 as the number of items in the scale approaches infinity. Psychol. Compared to other studies reporting the reliability and validity of the OSCE, this is the only report that has focused on the measurement tools and index defects in an internal medicine course. Finally, this study highlighted the deficits in reliability indexes, something that has not been the focus of many studies on the OSCE. This paper discusses the limitations of Cronbach's alpha as a sole index of reliability, showing how Cronbach's alpha is analytically handicapped to capture important measurement errors and scale dimensionality, and how it is not invariant under variations of scale length, interitem correlation, and sample characteristics. The Basic tier is always free. An examination of theory and applications. MHS: Contributed designing the study, analysis and interpretation of data and reviewed the initial draft manuscript. Med Educ. If you use Confirmatory Factor Analysis, this. 2023 by the Rector and Visitors of the University of Virginia. Estimating generalizability to a latent variable common to all of a scale's indicators: a comparison of estimators for h. Appl. National University of Distance Education (UNED), Spain. Cronbachs alpha is also not a measure of validity, or the extent to which a scale records the true value or score of the concept youre trying to measure without capturing any unintended characteristics. 26, 329367. Lord, F. M., and Novick, M. R. (1968). Available online at: http://www.stat-d.si/mz/mz15/socan.pdf, Tang, W., and Cui, Y. Psychometrika 42, 579591. Cronbachs alpha was created to measure the internal consistency of the exams [24]. Yes! RMSE and Bias with tau-equivalence and congeneric condition for 12 items, three sample sizes and the number of skewed items. PubMed We know that if we measure the same thing twice that the correlation between the two observations will depend in part by how much time elapses between the two measurement occasions. 2014;26:37986. Has many subtests that may be selected for use. Another important tool for assessing an exams reliability is factor analysis, which is used to quantify skills, ensure the components of the OSCE stations are homogeneous, and identify the structure of the exam [15, 16]. 2011;15:1728. Tau-equivalent model with = 0.558 for the six items > library(psych) > library(Rcsdp) > Cr <-matrix(c(1.00, 0.3114, 0.3114, 0.3114, 0.3114, 0.3114, 0.3114, 1.00, 0.3114, 0.3114, 0.3114, 0.3114, 0.3114, 0.3114, 1.00, 0.3114, 0.3114, 0.3114, 0.3114, 0.3114, 0.3114, 1.00, 0.3114, 0.3114, 0.3114, 0.3114, 0.3114, 0.3114, 1.00, 0.3114, 0.3114, 0.3114, 0.3114, 0.3114, 0.3114, 1.00), ncol = 6), > omega(Cr,1)$alpha # standardized Cronbach's [1] 0.731, > omega(Cr,1)$omega.tot # coefficient total [1] 0.731, > glb.fa(Cr)$glb # GLB factorial procedure [1] 0.731, > glb.algebraic(Cr)$glb # GLB algebraic procedure [1] 0.731, # Example 2. Our society should do whatever is necessary to make sure that everyone has an equal opportunity to succeed. 7:769. doi: 10.3389/fpsyg.2016.00769. Package psych. Available online at: http://org/r/psych-manual.pdf, Revelle, W., and Zinbarg, R. (2009). Coefficient alpha and beyond: issues and alternatives for educational research. The validity of the exam was measured by Pearsons correlation, which was strong. 30, 121144. The endocrinology and infectious disease stations were the best, followed by hematologyoncology, general medicine and respiratory system stations (Cronbachs alpha=0.80.9). ), Completely free for doi: 10.1007/s11336-008-9102-z, Shapiro, A., and ten Berge, J. M. F. (2000). Imagine that on 86 of the 100 observations the raters checked the same category. Micceri, T. (1989). Follow . Validity evidence for medical school OSCEs: associations with USMLE step assessments. Springer Nature. Psychometrika 65, 413425. They are: Whenever you use humans as a part of your measurement procedure, you have to worry about whether the results you get are reliable or consistent. Five of these scales can be summarized in two broader scales: (a) the delinquent behavior and aggressive behavior scales form the externalizing behavior scale and (b) the withdrawn, somatic complaints and anxious/depressed scales are combined in the internalizing behavior scale. Spearmans rank correlation was used to evaluate the correlation between the checklist and global rating scores. The R2 coefficient determinants, which were used to examine the linear correlation between the checklist and the global score, were 72, 82, and 78.2%. Spearmans rank correlation coefficient is used to assess the strength and direction of a relationship between two variables or to identify and test the strength of a relationship between two sets of data. Students were divided into groups as shown in Table1. Despite this, the impact of skewness on reliability estimation has been little studied. You might think of this type of reliability as calibrating the observers. Nevertheless, its limitations are well known (Lord and Novick, 1968; Cortina, 1993; Yang and Green, 2011), some of the most important being the assumptions of uncorrelated errors, tau-equivalence and normality. For example, word problems in an algebra class may indeed capture a students math ability, but they may also capture verbal abilities or even test anxiety, which, when factored into a test score, may not provide the best measure of her true math ability. 25, 6976. Chesser AM, Laing MR, Miedzybrodzka ZH, Brittenden J, Heys SD. Ameh N, Abdul MA, Adesiyun GA, Avidime S. Objective structured clinical examination vs traditional clinical examination: an evaluation of students perception and preference in a Nigerian medical school. Strong psychometric properties. EMO, MAG, AMH, ASB, AAD: Involved in data collection, analysis and interpretation of data and technical works. Your IP: Coefficients h and t are equivalent in unidimensional data, so we will refer to this coefficient simply as . Sijtsma (2009) shows in a series of studies that one of the most powerful estimators of reliability is GLBdeduced by Woodhouse and Jackson (1977) from the assumptions of Classical Test Theory (Cx = Ct + Ce)an inter-item covariance matrix for observed item scores Cx. doi: 10.1007/BF02289858, Teo, T., and Fan, X. Cronbach's Alpha: Review of Limitations . Medicine, Dentistry, Nursing & Allied Health. In this paper, using Monte Carlo simulation, the performance of these reliability coefficients under a one-dimensional model is evaluated in terms of skewness and no tau-equivalence. The assumption of uncorrelated errors (the error score of any pair of items is uncorrelated) is a hypothesis of Classical Test Theory (Lord and Novick, 1968), violation of which may imply the presence of complex multidimensional structures requiring estimation procedures which take this complexity into account (e.g., Tarkkonen and Vehkalahti, 2005; Green and Yang, 2015). It breaks down into two parts: the sum of the inter-item covariance matrix for item true scores Ct; and the inter-item error covariance matrix Ce (ten Berge and Soan, 2004). We started with Cronbachs alpha to measure the stability of the stations. 22, 209213. However, it need not be free of systematic erroranything that might introduce consistent and chronic distortion in measuring the underlying concept of interestin order to be reliable; it only needs to be consistent. Although it is considered a good index for station stability, it has some disadvantages: The measure is affected by exam time and dimensionality. Data Anal. Values closer to 1.0 indicate a greater internal consistency of the variables in the scale. Performance & security by Cloudflare. A Simulation Study for Comparing Three Lower Bounds to Reliability. Psychometrika 69, 613625. The rediscovery of bifactor measurement models. The number of medical students accepted into medical programs is increasing, which has made the traditional long/short case style of examination difficult to conduct. Streiner D. Starting at the beginning: an introduction to coefficient alpha and internal consistency. (2011). 1 Cronbach's alpha is a measure of inter-item reliability. Spearmans rank correlation and R2 coefficient determinants were used to correlate the checklist results with the global score to arrive at an internal consistency score. Analyses of the correlation of each item with its hypothesized scale revealed the Pearson's correlation coefficients to be 0.49-0.73 for the anxiety subscale and 0.56-0.71 for the depression subscale. academics and students, Inter-Rater or Inter-Observer Reliability, the analysis of the nonequivalent group design. In addition, as demonstrated in Table 3, the Cronbach's alpha coefficient was 0.892 with 95% confidence . Reliability of summed item scores using structural equation modeling: an alternative to coeficient Alpha. And, if your study goes on for a long time, you may want to reestablish inter-rater reliability from time to time to assure that your raters arent changing. software after being evaluated by Cronbach alpha reliability coefficient method and EFA . 2023 Analytics Simplified Pty Ltd, Sydney, Australia. Cronbach's alpha is a conservative measure (least lower bound for reliability) because it treats all of the items as making equal contributions. Assess. Correspondence to Alternatively, you might want to use the option reverse(ITEMS) to reverse the signs of any items/variables you list in between the parentheses. Methodol. Res. It is generally used as a measure of internal consistency or reliability of a psychometric instrument. Psychol. The internal consistency and reliability results improved in general, which can be explained by the time effect and the examiner misunderstanding the global score. Study with Quizlet and memorize flashcards containing terms like Identify 3 concepts that are related to reliability., What are the two types of tests for stability?, Match the following example with the appropriate test for internal consistency: "The odd items of the test had a high correlation with the even numbers . The test-retest estimator is especially feasible in most experimental and quasi-experimental designs that use a no-treatment control group. Test Theory: a Unified Treatment. doi: 10.1207/s15327906mbr3204_2, Raykov, T. (2001). An introduction and orientation about the OSCE was also given to each student group on the first day of the course. Share Cite Improve this answer Follow answered Mar 3, 2016 at 11:23 The resulting \( \alpha \) coefficient of reliability ranges from 0 to 1 in providing this overall assessment of a measures reliability. This website is using a security service to protect itself from online attacks. 75, 365388. The OSCE score analysis for the students is shown in detail in Table2. The principal results can be seen in Table 1 (6 items) and Table 2 (12 items). The parallel forms estimator is typically only used in situations where you intend to use the two forms as alternate measures of the same thing. First, this study was conducted on a single department within a single institution and involved only 4th-year medical students who agreed to the new examination format. Anal. R Development Core Team (2013). Psychometrika 74, 121135. Cronbach's alpha coefficient measures the internal consistency, or reliability, of a set of survey items. PubMed Central Pell G, Fuller R, Homer M, Roberts T. How to measure the quality of the OSCE: a review of metricsAMEE guide no. Res. By closing this message, you are consenting to our use of cookies. What is coefficient alpha? This approach also uses the inter-item correlations. Manage cookies/Do not sell my data we use in the preference centre. Psychometrika 80, 182195. A reliable measure is one that contains zero or very little random measurement errori.e., anything that might introduce arbitrary or haphazard distortion into the measurement process, resulting in inconsistent measurements. Nevertheless, in small samples, under the assumption of normality, it tends to overestimate the true reliability value (Shapiro and ten Berge, 2000); however its functioning under non-normal conditions remains unknown, specifically when the distributions of the items are asymmetrical. CAS McDonald, R. (1999). Congeneric model with 1 = 0.3, 2 = 0.4, 3 = 0.5, 4 = 0.6, 5 = 0.7, 6 = 0.8 > Cr <-matrix(c(1.00, 0.12, 0.15, 0.18, 0.21, 0.24, 0.12, 1.00, 0.20, 0.24, 0.28, 0.32, 0.15, 0.20, 1.00, 0.30, 0.35, 0.40, 0.18, 0.24, 0.30, 1.00, 0.42, 0.48, 0.21, 0.28, 0.35, 0.42, 1.00, 0.56, 0.24, 0.32, 0.40, 0.48, 0.56, 1.00), ncol = 6), > omega(Cr,1)$alpha # standardized Cronbach's [1] 0.717, > glb.fa(Cr)$glb # GLB factorial procedure [1] 0.754, Keywords: reliability, alpha, omega, greatest lower bound, asymmetrical measures, Citation: Trizano-Hermosilla I and Alvarado JM (2016) Best Alternatives to Cronbach's Alpha Reliability in Realistic Conditions: Congeneric and Asymmetrical Measurements. Trochim. Teach Learn Med. R syntax to estimate reliability coefficients from Pearson's correlation matrices. However, when there is a low or moderate test skewness GLBa should be used. Privacy In this case, the percent of agreement would be 86%. 2004;38:82531. How do I view content? doi:10.4103/0300-1652.137191. Descriptive statistics for modern test score distributions: skewness, kurtosis, discreteness, and ceiling effects. Although it is considered a good index for station stability, it has some disadvantages: The measure is affected by exam time and dimensionality.

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