A negative Cronbach's alpha indicates inconsistent coding (see assumptions) or a mixture of items measuring different dimensions, leading to negative inter-item correlations Cronbachs alfa (α) (engelska: Cronbach's alpha), är ett statistiskt mått på den interna konsistensen hos ett test, beskrivet som ett tal mellan 0 och 1. [1] Intern konsistens avser hur väl olika delar av ett test mäter samma bakomliggande koncept My Cronbach Alpha stated -0.656. The note below says: The value is negative due to a negative average covariance among items. This violates reliability model assumptions Cronbachs alfa (engelska: Cronbach's alpha) är ett statistiskt mått på den interna konsistensen hos ett test eller index, beskrivet som ett tal mellan 0 och 1. Intern konsistens avser hur väl olika delar av ett sammanslaget index mäter samma bakomliggande koncept. Cronbachs alfa betecknas vanligen med den grekiska bokstaven alfa, α Tau-equivalent reliability (), also known as Cronbach's alpha or coefficient alpha, is the most common test score reliability coefficient for single administration (i.e., the reliability of persons over items holding occasion fixed).. Recent studies recommend not using it unconditionally. Reliability coefficients based on structural equation modeling (SEM) are often recommended as its alternative

Below, for conceptual purposes, we show the formula for the Cronbach's alpha: α = N c ¯ v ¯ + ( N − 1) c ¯. Here N is equal to the number of items, c ¯ is the average inter-item covariance among the items and v ¯ equals the average variance Cronbach's alpha is a measure used to assess the reliability, or internal consistency, of a set of scale or test items. In other words, the reliability of any given measurement refers to the extent to which it is a consistent measure of a concept, and Cronbach's alpha is one way of measuring the strength of that consistency

Cronbach's Alpha ranges between 0 and 1, with higher values indicating that the survey or questionnaire is more reliable. When reporting the value of Cronbach's Alpha in a final report, you need to include the following two values: The number of items used on the subscale. The value of Cronbach's Alpha Cronbach's alpha is the most common measure of internal consistency (reliability). It is most commonly used when you have multiple Likert questions in a survey/questionnaire that form a scale and you wish to determine if the scale is reliable ghada8888 said: Hi to all, I have a question about the Cronbach's Alpha. The value that I got is -.30 which is negative! And I found this comment on the spss output: The value is negative due to a negative average covariance among items. This violates reliability model assumptions. You may want to check item coding Cronbach's alpha is certainly among the most used statistics in the social sciences, but many students and researchers don't really know what it tells us - or how to interpret it. Fortunately, Chad Marshall wrote a wonderful introduction to Cronbach's Alpha, below. Chad Marshall is currently a DBA student in the Mitchell College of Business at the University of South Alabama

Cronbachsches Alpha. (Alpha) ist eine nach Lee Cronbach benannte Maßzahl für die interne Konsistenz einer Skala und bezeichnet das Ausmaß, in dem die Aufgaben bzw. Fragen einer Skala miteinander in Beziehung stehen (interrelatedness ). Es ist hingegen kein Maß für die Eindimensionalität einer Skala **Cronbachs** alfa is een maat voor interne consistentie oftewel voor de homogeniteit van de vragen. Een hoge score, zeg groter dan 0,70, wijst op een hoge mate van betrouwbaarheid zodat je een somscore kunt maken. Alles wat je moet weten over onderzoek vind je in het Online Kenniscentrum Onderzoek en Statistiek >>> 克朗巴哈系数（Cronbach's alpha或Cronbach's α）是一个统计量，是指量表所有可能的项目划分方法的得到的折半信度系数的平均值，是最常用的信度测量方法。. 它最先被美国教育学家Lee Cronbach在1951年命名。. 若一份量表有n题，题间的平均相关系数为r，则此量表的标准化α系数为α=nr/ [ (n-1)r+1]。 크론바흐 알파 (Cronbach's α)란.. 1951년 Lee Cronbach가 만들었으며, Likert scale 형식의 설문, 혹은 그와 비슷한 시험 등의 문항에 대한. 내적일관성 (Internal Consistency)을 측정하는 척도를 말합니다. 알파값 또는 알파계수, 크론바흐 계수 등으로 불리며, 이 크론바흐 알파 값은 0 ~ 1 사이의 값을 범위로. 가집니다. 동일한 개념 혹은 동일 구성으로 되었는지 측정을 하여 Survey나. Cronbach's alpha is een manier om vast te stellen of meerdere items samen één schaal mogen vormen. Het wordt ook wel een betrouwbaarheidsanalyse genoemd. De Cronbach's alpha zelf is de maatstaf. Dit wordt getoetst op basis van de onderlinge correlatie van de verschillende items

Cronbach's alpha will generally increase when the correlations between the items increase. For this reason the coefficient measures the internal consistency of the test. Its maximum value is 1, and usually its minimum is 0, although it can be negative (see below) * Cronbach's alpha is a statistic commonly quoted by authors to demonstrate that tests and scales that have been constructed or adopted for research projects are fit for purpose*. Cronbach's alpha is regularly adopted in studies in science education: it was referred to in 69 different papers published in 4 leading science education journals in a single year (2015)—usually as a measure of.

L'alpha di Cronbach è l'indice statistico più utilizzato per valutare l'affidabilità delle dimensioni di un test o di un questionario.In questo articolo scoprirai quando utilizzarlo e quando no, come interpretarlo in modo corretto e anche quali sono le principali alternative.. Indici di affidabilità: cosa sono. Secondo la Teoria Classica dei Test (TCT), qualsiasi misurazione. Cronbach's alpha (of: Cronbachs alfa in het Nederlands) wordt gebruikt om de mate van samenhang (interne consistentie) tussen meerdere enquêtevragen te meten. Voorbeeld: Je wilt klanttevredenheid meten met drie vragen: Hoe schoon vind je de winkel?, Ben je tevreden met het assortiment? en Hoe waardeer je de behulpzaamheid van het personeel? * Cronbachs α is een maat voor de betrouwbaarheid van psychometrische tests of van vragenlijsten*. De waarde van α {\displaystyle \alpha } is een schatting voor de ondergrens van de betrouwbaarheid van de betrokken test. Om een schatting te bepalen van de betrouwbaarheid van een test zijn ten minste twee testafnames nodig. Op basis van één testafname kan Cronbachs α {\displaystyle \alpha } berekend worden om zo een schatting van de ondergrens te verkrijgen. Cronbachs α.

* Cronbach's Alpha is the dominant measure of scale reliability in psychology and the social sciences*. Its importance can't be overstated and you'll find it in almost every quantitative empirical study you'll read. Surprisingly, there hasn't been a single article published on Medium covering its application in Python Cronbach's Alpha ranges between 0 and 1, with higher values indicating that the survey or questionnaire is more reliable. The easiest way to calculate Cronbach's Alpha is to use the cronbach.alpha() function from the ltm package. This tutorial provides an example of how to use this function in practice Cronbach's alpha using Minitab Introduction. Cronbach's alpha is a common measure of internal consistency (reliability), often used when you have multiple Likert questions in a survey/questionnaire that form a scale and you want to determine if the scale is reliable This video describes how to calculate and interpret Cronbach's alpha using SPSS Cronbach's Alpha Reliability Coefficient for Likert-Type Scales Joseph A. Gliem Rosemary R. Gliem Abstract: The purpose of this paper is to show why single-item questions pertaining to a construct are not reliable and should not be used in drawing conclusions. By comparing the reliability of a summated

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 Cronbach's alpha is a coefficient of internal reliability, and it is a function (essentially) of the average correlation. It is larger for a larger number of items in the scale with the same average r. It can be negative when you have negative correlations If your Cronbach Alpha is low, that means some of your items are not representatives of the domain of behaviour. What you can do to improve the reliability is to remove some odd items (items less than 0.30) in the internal consistency (i.e if you have so many items) and the overall coefficient will shoot up

Cronbach's alpha gives us a simple way to measure whether or not a score is reliable. It is used under the assumption that you have multiple items measuring the same underlying construct: so, for the Happiness Survey, you might have five questions all asking different things, but when combined, could be said to measure overall happiness ** Cronbach's Alpha (Reliability of test scores) The Jefferson Scale of Empathy consisted of 20 items with three subscales**. The Perspective Taking subscale consisted of 10 items (Alpha = 0.74), the Compassionate Care subscale consisted of 8 items (Alpha = 0. 70), and the Waking in the Patient's Shoes subscale consisted of 2 items (Alpha= 0.58) Cronbach's alpha tests to see if multiple-question Likert scale surveys are reliable. These questions measure latent variables — hidden or unobservable variables like: a person's conscientiousness, neurosis or openness. These are very difficult to measure in real life

Bild 4. Hur man testar för Cronbach's alpha. Man får då ut output som ser ut som i Bild 5. Det intressantaste är rutan Reliability statistics. Där står det i kolumnen Cronbach's Alpha ett värde som kan variera mellan 0 och 1, där högre värden betyder högre reliabilitet. I det här fallet blir värdet ,602 35264: Can I get Cronbach's coefficient alpha from JMP®? Yes. Choose Analyze Multivariate Methods Multivariate , specify your continuous columns in the dialog box, and click OK to create the analysis. In the output window, click on the Multivariate red triangle menu and select Item Reliability Cronbach's α, or Standardized α for Cronbach's. Before alpha, researchers were limited to estimating internal consistency of only dichotomously scored items using the KR-20 formula. Cronbach's (1951) alpha was developed based on the necessity to evaluate items scored in multiple answer categories. Cronbach (1951) derived the alpha formula from the KR-20 formula: KR - 20 K / (K -1) [1 - / 2)]

Cronbach's Alpha coefficient α (Cronbach, 1951) is such a lower bound for the reliability, that is, Rel(O) >= α. The standardized Cronbach α coefficient is defined as the following: Where is the mean correlation of all n items from the scale So alpha should be 1, as high as it can get. But Cronbach would suggest you are wasting researcher and participant effort by having many items if they all elicit the same response. The point of scales having several items is that we assume no one item directly catches perfectly what we are trying to measure. Whether they do or not, there is no. This study disproves the following six common misconceptions about coefficient **alpha**: (a) **Alpha** was first developed by **Cronbach**. (b) **Alpha** equals reliability. (c) A high value of **alpha** is an indication of internal consistency. (d) Reliability will always be improved by deleting items using **alpha** if item deleted. ** Those who have access to Microsoft Excel, they can carry out the same calculation in an Excel ® spreadsheet as described above**. It was possible to calculate α of a questionnaire with the help of free computer software. Cronbach's alpha for any number of questions and responses can be calculated in similar fashion

- Typically, I begin my guides with a brief review of the statistic; however, one of my prior DBA students, Chad Marshall, wrote a fantastic introduction to Cronbach's alpha which was previously featured on MattCHoward.com.. If you need to learn more about Cronbach's alpha, click here to read it. Once you are familiar with Cronbach's alpha, we can then use R to calculate it
- Cronbach's alpha showed the questionnaire to reach acceptable reliability, α = 0.81. Most items appeared to be worthy of retention, resulting in a decrease in the alpha if deleted. The one exception to this was item 4, which would increase the alpha to α = 0.83. As such, removal of this item should be considered
- Tavakol et al. Cronbach's alpha 54 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 underes

Cronbach's alpha. Cronbach's alpha is a way of assessing reliability by comparing the amount of shared variance, or covariance, among the items making up an instrument to the amount of overall variance. The idea is that if the instrument is reliable, there should be a great deal of covariance among the items relative to the variance ** Cronbach's alpha Cronbach's Alpha Based on Standardized Items N of Items 0**.724 0.659 10 Table (1 to 4) shows the item-analysis output from SPSS for the multi-item scale of paediatrician attitude towards self-esteem. The terms used in this study can be interpreted as follows: Scale statistics: These are summary statistics for the 1

- is Cronbach's alpha, although this was not explicitly stated. As such examples can only be assumed to report the Cronbach alpha (as there are other statistics labelled alpha), they were not included in the survey, and no attempt was made to systematicallyidentify such papers in thesampled volumes
- Cronbach's alpha is a statistic. It is generally used as a measure of internal consistency or reliability of a psychometric instrument. In other words, it measures how well a set of variables or items measures a single, one-dimensional latent aspect of individuals. Generally, many quantities of interest in medicine, such as anxiety or degree.
- Alpha is a very nice command used to calculate Cronbach's alpha for scales. The basic syntax is simply alpha [variables in the scale] and requires at least two items. Then there are a few options which can be used to finetune the command. First of all, the reverse (variable list) causes Stata to reverse score items for you

Statistics - Using Cronbach Alpha This first week of CECS 6510 Dr. Knezek had us look at correlations using Pearson Correlations, reliability and validity computing Cronbach Alpha to measure internal consistency, and effect size using Cohen's D. What kicks me is that it is fascinating to me and I only want to read more abou How to say Cronbach's alpha in English? Pronunciation of Cronbach's alpha with 2 audio pronunciations and more for Cronbach's alpha Thoughts on Cronbach's Coefficient Alpha I have a few thoughts to share on coefficient alpha, the ubiquitous and frequently misused psychometric index of internal consistency reliability. These thoughts aren't new, people have thought and written about them before (references below), but they're worth repeating, as the majority of those who cite Cronbach (1951) seem to be unaware that cronbach.alpha () returns an object of class cronbachAlpha with components. the value of Cronbach's alpha. the number of sample units. the number of items. a copy of the standardized argument. the name of argument data. the confidence interval for alpha; returned if CI = TRUE. a copy of the probs argument; returned if CI = TRUE

Cronbach Coefficient Alpha. Variables. Alpha. Raw. 0.822134. Standardized. 0.985145. Because the variances of some variables vary widely, you should use the standardized score to estimate reliability. The overall standardized Cronbach's coefficient alpha of 0.985145 provides an acceptable lower bound for the reliability coefficient Cronbach's Alpha coefficient (Cronbach, 1951) is such a lower bound for the reliability, that is, Rel(O) >= . The standardized Cronbach coefficient is defined as the following: Where ̅is the mean correlation of all n items from the scale. Theoretically ranges from - t Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16, 297-334 (28,307 citations in Google Scholar as of 4/1/2016). Klaas Sijtsma—Tilburg University, The Netherlands . E-mail: k.sijtsma@tilburguniversity.edu. By far the most cited article in Psychometrika is Lee Cronbach's famous study of. Cronbach's alpha examines reliability by determining the internal consistency of a test or the average correlation of items (variables) within the test. In Stata, the .alpha command conducts the reliability test. For example, suppose you wish to test the internal reliability of ten variables, v1 through v10

The Problem with Cronbach's Alpha: Comment on Sijtsma and Van der Ark (2015) Abstract Knowledge of a scale's dimensionality is an essential preliminary step to the application of any measure of reliability derived from classical test theory--an approach commonly used is nursing research I think it is easier to consider the relationship between Cronbach's alpha and the the Pearson correlation in Standardized form as: α = k¯ρ 1+(k−1)¯ρ α = k ρ ¯ 1 + ( k − 1) ρ ¯. where k is the number of classes (e.g. # of test items, # of raters). Thus, coefficient alpha can be considered as a function of the average of the. Cronbach's alpha for any number of questions and responses can be calculated in similar fashion. This article would help researchers in resource-poor setting for calculation of Cronbach's alpha. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms

Cronbachs alfa (α) (engelska: Cronbach's alpha), är ett statistiskt mått på den interna konsistensen hos ett test, beskrivet som ett tal mellan 0 och 1. [1] Intern konsistens avser hur väl olika delar av ett test mäter samma bakomliggande koncept. En enkätundersökning kan tänkas innehålla ett antal olika frågor för att mäta ett personlighetsdrag hos deltagarna Cronbach's alpha can be carried out in SPSS Statistics using the Reliability Analysis procedure. In this section, we set out this 7-step procedure depending on whether you have version 26 (or the subscription version ) of SPSS Statistics or version 25 or earlier Internal consistency is usually measured with Cronbach's alpha, a statistic calculated from the pairwise correlations between items. Internal consistency ranges between negative infinity and one. Coefficient alpha will be negative whenever there is greater within-subject variability than between-subject variability The Cronbach's alpha coefficients based on the empirical covariance S, Wilcox midvariance W and T3 were 0.72, 0.72 and 0.73, respectively. On the other hand, robust Cronbach's alpha coefficients based on RMCD and the biweight S-estimator both are 0.77

Cronbach's alpha. Författad av Ronny Gunnarsson och publicerad första gången January 28, 2018. Senast reviderad September 8, 2019. Du måste hänvisa till denna webbsida om du använder informationen någon annanstans. Hur detta skall se ut beror på var du återanvänder informationen Yes. Choose Analyze Multivariate Methods Multivariate, specify your continuous columns in the dialog box, and click OK to create the analysis.In the output window, click on the Multivariate red triangle menu and select Item Reliability Cronbach's α, or Standardized α for Cronbach's α, standardized.. Operating System and Release Informatio

Cronbach's α, Revelle's β, and McDonald's ω H: Their relations with each other and two alternative conceptualizations of reliability. Psychometrika, 70 (1), 123 - 133 . Google Scholar | Crossref | IS Cronbach's alpha with delete removes the question you're reviewing and recalculates the exam's overall reliability (i.e., Cronbach's Alpha, sometimes called, Correlation Alpha or Alpha for short) calculation without it. Here's an exceptional blog post on Cronbach's Alpha by Dr. Charles Zaiontz Although Cronbach's alpha is the most widely applied index of internal consistency reliability, there are misconceptions about its use and interpretation. This paper aims to guide assessment developers in paediatric occupational therapy, as well as practitioners who are evaluating outcome measures in using and interpreting the Cronbach's alpha estimates appropriately We can still add Cronbach's alpha (when it has unit tests), but I think it would be more useful to have an alternative that is more accepted in the recent literature, and to which we can point the users. Copy link vinyll commented May 20, 2017 • edited.

Cronbach's Alpha Cronbach‟s alpha is perhaps the most common estimate of internal consistency of items in a scale (Cronbach, 1951; Cronbach & Shavelson, 2004). Alpha measures the extent to which item responses (answers to survey questions) correlate with each other. In other words, The function of data analysis is to facilitate in testing hypotheses. There are 4 statistical tools will be carried out to analyse the results that are Cronbach's Alpha, Descriptive statistic, Person Correlation Coefficient and Simple Linear Regression. Firstly, reliability statistics will be analysed by using Cronbach's Alpha COEFFICIENT ALPHA 383 the year 1960 (the year in which citations of Cronbach's work began to appear) and ending with 1992. This meant that every article published in these journals wa What are some citations to use for Cronbach's Alpha? Green, S.B., Lissitz, R.W., and Mulaik, S.A.(1977) Limitations of coefficient alpha as an index of test unidimensionality. Educational and Psychological Measurement, 37, 827-838. Hattie, J. (1985) Methodology Review: Assessing unidimensionality of tests and items SPSS Statistics does not have an option within the Reliability procedure or other procedures to test group difference between Cronbach alphas or ICCs for a set of items. (The Average Measures ICC for the 2-way mixed model is equal to Cronbach's alpha. ) One formula for this test is provided in a paper by Feldt, Woodruff, & Salih (1987)

This discussion paper argues that both the use of **Cronbach's** **alpha** as a reliability estimate and as a measure of internal consistency suffer from major problems. First, **alpha** always has a value, which cannot be equal to the test score's reliability given the interitem covariance matrix and the usual R has the package psych which allows one to calculate the Cronbach's alpha very easily just by one line: psych::alpha(your_data, column_list) For Python, the situation is more tricky since there does not seem to exist any package for calculating Cronbach's alpha. Fortunately, the formula is not very complicated and it can be calculated in The Cronbach's alpha for each group was 0.7, 0.8, and 0.9. Correlations for all stations ranged from 0.7 to 0.8, which indicated good stability and internal consistency with minor differences in the progression of the indexes. The reliability of the written exam was 0.79,.

MINIMUM SAMPLE SIZE FOR CRONBACH'S COEFFICIENT ALPHA: A MONTE-CARLO STUDY CRONBACH ALFA KATSAYISI İÇİN MİNİMUM ÖRNEKLEM GENİŞLİĞİ: MONTE-CARLO ÇALIŞMASI Halil YURDUGÜL* ABSTRACT: The coefficient alpha is the most widely used measure of internal consistency for composite scores in the educational and psychological studies Cronbach's alpha results will show as follows: Conclusion: Cronbach's alpha of the scale was 0.869, the Corrected Item-Total Correlation in the scale are greater than 0.3 and no cases eliminate observed variables that can make the Cronbach's alpha of the scale this is greater than 0.869( last column) Understanding Cronbach's Alpha in SPSS. In this section, we are going to learn about Cronbach's alpha.Cronbach's alpha is a coefficient that gives us the measure of internal consistency of a test. By internal consistency, we mean to what extent the indicators of the test are related to each other and to what extent they are conversing on the main global construct that they are trying to address >AlphaA Cronbach's alpha for the 'DadosA[, -1:-5]' data-set Items: 53 Sample units: 62 alpha: 0.897 >AlphaB Cronbach's alpha for the 'DadosB[, -1:-5]' data-set Items: 53 Sample units: 71 alpha: 0.871 Which is the expected result! My doubt is how to insert only the alpha value in Knit, not all data. I have tried doing this: `r AlphaA` `r AlphaB

Find two estimates of reliability: Cronbach's alpha and Guttman's Lambda 6. Description. Internal consistency measures of reliability range from omega_hierchical to alpha to omega_total.This function reports two estimates: Cronbach's coefficient alpha and Guttman's lambda_6.Also reported are item - whole correlations, alpha if an item is omitted, and item means and standard deviations Cronbach's Alpha. Cronbach's alpha values are quite sensitive to the number of items in the scale. With short scales (e.g. scales with fewer than ten items) it is common to find quite low Cronbach's values (e.g. .5). Reliability is normally reported under the head of instrumentation in the methodology section I made some code for calculating Cronbach Alpha that works. But I am not too good using lambda functions. Is there a way to reduce the code and improve efficiency by using lambda instead of the sva.. If Cronbach's alpha is below 0.7, then the items may not reliably measure a single skill or characteristic to conclude that at least some of the items measure the same characteristic. However, the appropriate benchmark value to use also depends on the standards in your subject area and the number of items in the analysis The Cronbach Coefficient Alpha with Deleted Variables table in Output 2.6.4 does not show significant increase or decrease in the standardized alpha coefficients. See the section Cronbach's Coefficient Alpha for more information about Cronbach's alpha

Cronbach's alpha generally increases when the correlations between the items increase. For this reason the coefficient is also called the internal consistency or the internal consistency reliability of the test. Range. The value of alpha (α) may lie between negative infinity and 1. However only positive values of α make sense Step 3: Then the following dialog box will open.Drag the questions to the right in the item box for which you want to calculate Cronbach's Alpha. Here, the example variables measure the construct Means of communication, so I dragged the questions related to means of communications to the right box such as wireless, multiline, voice mail, pager, internet and so on Assumptions of Cronbach's Alpha in SPSS. In this section, we are going to learn about the assumptions of Cronbach's alpha in SPSS. Now we have seen people indiscriminately apply the Cronbach alpha without even bothering for the assumptions. That's fine if we have a large sample size Cronbach's alpha (Cronbach1951) assesses the reliability of a summative rating (Likert1932) scale composed of the variables (called items) speciﬁed. The set of items is often called a test or battery. A scale is simply the sum of the individual item scores, reversing the scoring for statement

Cronbach's Coefficient Alpha: A Meta-Analysis Study* Cronbach Alfa Katsayısı: Bir Meta Analizi Çalıúması Hatice İNAL , Esin YILMAZ KOĞAR , Eda DEMİRDÜZEN , Selahattin GELBAL Received: 10.03.2016 Accepted: 28.03.2016 Published: 31.01.201 and Cronbach's Alpha An Example - Melanie Hof - 1. Introduction The pleasure writers experience in writing considerably inﬂuences their motivation and consequently their writing performance (Hayes, 1996). Low-motivated writers perform worse, since they spend les the Cronbach's alpha value is low (near to 0), it means some or all of the items are not measuring the same dimension (2-3). To cite this article: Mohamad Adam B, Evi Diana O, Nur Akmal B. A review on sample size determination for Cronbach's alpha test: a simple guide for researchers Lee J. Cronbach アメリカの心理学者・教育学者 1916年～2001年 Stanford University School of Education Cronbach, L. J. 1951 Coefficient alpha and the internal structure of tests. Psychometrika, 16, 297-334