Arabic
Bulgarian
Chinese
Croatian
Czech
Danish
Dutch
English
Estonian
Finnish
French
German
Greek
Hebrew
Hindi
Hungarian
Icelandic
Indonesian
Italian
Japanese
Korean
Latvian
Lithuanian
Malagasy
Norwegian
Persian
Polish
Portuguese
Romanian
Russian
Serbian
Slovak
Slovenian
Spanish
Swedish
Thai
Turkish
Vietnamese

Arabic
Bulgarian
Chinese
Croatian
Czech
Danish
Dutch
English
Estonian
Finnish
French
German
Greek
Hebrew
Hindi
Hungarian
Icelandic
Indonesian
Italian
Japanese
Korean
Latvian
Lithuanian
Malagasy
Norwegian
Persian
Polish
Portuguese
Romanian
Russian
Serbian
Slovak
Slovenian
Spanish
Swedish
Thai
Turkish
Vietnamese

definition of Wikipedia

Advertizing ▼

**Cronbach's (alpha)**^{[1]} is a coefficient of reliability. It is commonly used as a measure of the internal consistency or reliability of a psychometric test score for a sample of examinees. It was first named alpha by Lee Cronbach in 1951, as he had intended to continue with further coefficients. The measure can be viewed as an extension of the Kuder-Richardson Formula 20 (KR-20), which is an equivalent measure for dichotomous items. Alpha is not robust against missing data. Several other Greek letters have been used by later researchers to designate other measures used in a similar context.^{[2]} Somewhat related is the average variance extracted (AVE).

This article discusses the use of in psychology, but Cronbach's alpha statistic is widely used in the social sciences, business, nursing, and other disciplines. The term *item* is used throughout this article, but items could be anything — questions, raters, indicators — of which one might ask to what extent they "measure the same thing." Items that are manipulated are commonly referred to as *variables*.

## Contents |

Cronbach's is defined as

where is the number of components (*K-items* or *testlets*), the variance of the observed total test scores, and the variance of component *i* for the current sample of persons. See Develles (1991).

Alternatively, the Cronbach's can also be defined as

where is as above, the average variance, and the average of all covariances between the components across the current sample of persons.

The *standardized Cronbach's alpha* can be defined as

where is as above and the mean of the non-redundant correlation coefficients (i.e., the mean of an upper triangular, or lower triangular, correlation matrix).

Cronbach's is related conceptually to the Spearman–Brown prediction formula. Both arise from the basic classical test theory result that the reliability of test scores can be expressed as the ratio of the true-score and total-score (error plus true score) variances:

Theoretically, alpha varies from zero to 1, since it is the ratio of two variances. Empirically, however, alpha can take on any value less than or equal to 1, including negative values, although only positive values make sense ^{[3]}. Higher values of alpha are more desirable. Some professionals^{[4]} as a rule of thumb, require a reliability of 0.70 or higher (obtained on a substantial sample) before they will use an instrument. Obviously, this rule should be applied with caution when has been computed from items that systematically violate its assumptions.^{[specify]} Furthermore, the appropriate degree of reliability depends upon the use of the instrument. For example, an instrument designed to be used as part of a battery of tests may be intentionally designed to be as short as possible, and therefore somewhat less reliable. Other situations may require extremely precise measures with very high reliabilities.

This has resulted in a wide variance of test reliability. In the case of psychometric tests, most fall within the range of 0.75 to 0.83 with at least one claiming a Cronbach alpha above 0.90 (Nunnally 1978, page 245-246).

Main article: Internal consistency

Cronbach's alpha will generally increase as the intercorrelations among test items increase, and is thus known as an internal consistency estimate of reliability of test scores. Because intercorrelations among test items are maximized when all items measure the same construct, Cronbach's alpha is widely believed to indirectly indicate the degree to which a set of items measures a single unidimensional latent construct. However, the average intercorrelation among test items is affected by skew just like any other average. Thus, whereas the modal intercorrelation among test items will equal zero when the set of items measures several unrelated latent constructs, the average intercorrelation among test items will be greater than zero in this case. Indeed, several investigators have shown that alpha can take on quite high values even when the set of items measures several unrelated latent constructs (e.g., Cortina, 1993; Cronbach, 1951; Green, Lissitz & Mulaik, 1977; Revelle, 1979; Schmitt, 1996; Zinbarg, Yovel, Revelle & McDonald, 2006). As a result, alpha is most appropriately used when the items measure different substantive areas within a single construct. When the set of items measures more than one construct, coefficient omega_hierarchical is more appropriate (McDonald, 1999; Zinbarg, Revelle, Yovel & Li, 2005).

Alpha treats any covariance among items as *true-score* variance, even if items covary for spurious reasons. For example, alpha can be artificially inflated by making scales which consist of superficial changes to the wording within a set of items or by analyzing speeded tests.

A commonly accepted rule of thumb for describing internal consistency using Cronbach's alpha is as follows^{[5]}^{[6]}, however it should be noted that a greater number of items in the test can artificially inflate the value of alpha^{[7]} and so this rule of thumb should be used with caution:

Cronbach's alpha |
Internal consistency |
---|---|

α ≥ .9 | Excellent |

.9 > α ≥ .8 | Good |

.8 > α ≥ .7 | Acceptable |

.7 > α ≥ .6 | Questionable |

.6 > α ≥ .5 | Poor |

.5 > α | Unacceptable |

Cronbach and others generalized some basic assumptions of classical test theory in their generalizability theory. If this theory is applied to test construction, then it is assumed that the items that constitute the test are a random sample from a larger universe of items. The expected score of a person in the universe is called the universe score, analogous to a true score. The generalizability is defined analogously as the variance of the universe scores divided by the variance of the observable scores, analogous to the concept of reliability in classical test theory. In this theory, Cronbach's alpha is an unbiased estimate of the generalizability. For this to be true the assumptions of essential -equivalence or parallelness are not needed. Consequently, Cronbach's alpha can be viewed as a measure of how well the sum score on the selected items capture the expected score in the entire domain, even if that domain is heterogeneous.

Cronbach's alpha is said to be equal to the stepped-up consistency version of the intra-class correlation coefficient, which is commonly used in observational studies. But this is only conditionally true. In terms of variance components, this condition is, for item sampling: if and only if the value of the item (rater, in the case of rating) variance component equals zero. If this variance component is negative, alpha will underestimate the stepped-up intra-class correlation coefficient; if this variance component is positive, alpha will overestimate this stepped-up intra-class correlation coefficient.

Cronbach's alpha also has a theoretical relation with factor analysis. As shown by Zinbarg, Revelle, Yovel and Li (2005), alpha may be expressed as a function of the parameters of the hierarchical factor analysis model which allows for a general factor that is common to all of the items of a measure in addition to group factors that are common to some but not all of the items of a measure. Alpha may be seen to be quite complexly determined from this perspective. That is, alpha is sensitive not only to general factor saturation in a scale but also to group factor saturation and even to variance in the scale scores arising from variability in the factor loadings. Coefficient omega_hierarchical (McDonald, 1999; Zinbarg, Revelle, Yovel & Li, 2005) has a much more straightforward interpretation as the proportion of observed variance in the scale scores that is due to the general factor common to all of the items comprising the scale.

This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (December 2009) |

**^**Cronbach (1951)**^**Revelle & Zinbarg (2009)**^**Ritter, N. (2010). Understanding a widely misunderstood statistic: Cronbach's alpha. Paper presented at Southwestern Educational Research Association (SERA) Conference 2010, New Orleans, LA (ED526237).**^**Nunnally (1978)**^**George, D., & Mallery, P. (2003). SPSS for Windows step by step: A simple guide and reference. 11.0 update (4th ed.). Boston: Allyn & Bacon.**^**Kline, P. (1999). The handbook of psychological testing (2nd ed.). London: Routledge**^**Cortina, J.M. (1993). What is coefficient alpha? An examination of theory and applications. Journal of Applied Psychology, 78, 98-104.

- Allen, M.J., & Yen, W. M. (2002).
*Introduction to Measurement Theory.*Long Grove, IL: Waveland Press. - Bland J.M., Altman D.G. (1997). Statistics notes: Cronbach's alpha. BMJ 1997;314:572.
- Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests.
*Psychometrika, 16(3)*, 297-334. - Cronbach, Lee J., and Richard J. Shavelson. (2004). My Current Thoughts on Coefficient Alpha and Successor Procedures.
*Educational and Psychological Measurement*64, no. 3 (June 1): 391-418. doi:10.1177/0013164404266386. - Cortina. J. M. ( 1993). What is coefficient alpha? An examination of theory and applications.
*Journal of Applied Psychology, 78*, 98- 104. - Devellis, R.F. (1991).
*Scale Development*, Sage Publications, pp. 24–33. - Green, S. B., Lissitz, R.W., & Mulaik, S. A. (1977). Limitations of coefficient alpha as an index of test unidimensionality.
*Educational and Psychological Measurement, 37*, 827–838. - McDonald, R. P. (1999).
*Test Theory: A Unified Treatment*, Erlbaum, pp. 90–103.ISBN 0805830758 - Nunnally, J. C. (1978). Psychometric theory (2nd ed.). New York: McGraw-Hill.
- Revelle, W. (1979). Hierarchical cluster analysis and the internal structure of tests.
*Multivariate Behavioral Research, 14*, 57-74. - Revelle, W., Zinbarg, R. (2009) "Coefficients Alpha, Beta, Omega, and the glb: Comments on Sijtsma",
*Psychometrika*, 74(1), 145–154. [1] - Schmitt, N. (1996). Uses and abuses of coefficient alpha.
*Psychological Assessment, 8*, 350-353. - Zinbarg, R., Revelle, W., Yovel, I. & Li, W. (2005). Cronbach’s , Revelle’s , and McDonald’s : Their relations with each other and two alternative conceptualizations of reliability.
*Psychometrika, 70*, 123-133. - Zinbarg, R., Yovel, I., Revelle, W. & McDonald, R. (2006). Estimating generalizability to a universe of indicators that all have an attribute in common: A comparison of estimators for .
*Applied Psychological Measurement, 30*, 121 – 144.

sensagent's content

- definitions
- synonyms
- antonyms
- encyclopedia

Dictionary and translator for handheld

New : sensagent is now available on your handheld

Advertising ▼

Webmaster Solution

Alexandria

A windows (pop-into) of information (full-content of Sensagent) triggered by double-clicking any word on your webpage. Give contextual explanation and translation from your sites !

SensagentBox

With a SensagentBox, visitors to your site can access reliable information on over 5 million pages provided by Sensagent.com. Choose the design that fits your site.

Business solution

Improve your site content

Add new content to your site from Sensagent by XML.

Crawl products or adds

Get XML access to reach the best products.

Index images and define metadata

Get XML access to fix the meaning of your metadata.

Please, email us to describe your idea.

Lettris

Lettris is a curious tetris-clone game where all the bricks have the same square shape but different content. Each square carries a letter. To make squares disappear and save space for other squares you have to assemble English words (left, right, up, down) from the falling squares.

boggle

Boggle gives you 3 minutes to find as many words (3 letters or more) as you can in a grid of 16 letters. You can also try the grid of 16 letters. Letters must be adjacent and longer words score better. See if you can get into the grid Hall of Fame !

English dictionary

Main references

Most English definitions are provided by WordNet .

English thesaurus is mainly derived from The Integral Dictionary (TID).

English Encyclopedia is licensed by Wikipedia (GNU).

Copyrights

The wordgames anagrams, crossword, Lettris and Boggle are provided by Memodata.

The web service Alexandria is granted from Memodata for the Ebay search.

The SensagentBox are offered by sensAgent.

Translation

Change the target language to find translations.

Tips: browse the semantic fields (see From ideas to words) in two languages to learn more.

last searches on the dictionary :

Quartz ·
Hnivan ·
Alan A'Court ·
Mila Mulroney ·
Urinalysis ·
Aloha Week ·
1356 ·
Affeton Castle ·
Georgeta Damian ·
ANTONI LITERES ·

3928 online visitors

computed in 0.046s

I would like to report:

section :

a spelling or a grammatical mistake

an offensive content(racist, pornographic, injurious, etc.)

a copyright violation

an error

a missing statement

other

please precise: