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help for factortest                                          Joao Pedro Azevedo
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Calculate specification tests before factor or pca


        factortest [varlist] [if exp] [in range]


Description

    factortest performs the Bartlett's test for sphericity and the
    Kaiser-Meyer-Olkin Measure of Sampling Adequacy. Both tests should be
    used prior to a factor or a principal component analysis.


Technical details

    Determinant of the matrix of correlation: This determinant will equal 1.0
    only if all correlations equal 0, otherwise the determinant will be less
    than 1.

    Bartlett's test for sphericity: Calculates the determinant of the matrix
    of the sums of products and cross-products (S) from which the
    intercorrelations matrix is derived. The determinant of the matrix S is
    converted to a chi-square statistic and tested for significance.
    
    The null hypothesis is that the intercorrelation matrix comes from a
    population in which the variables are noncollinear (i.e. an identity
    matrix), and that the non-zero correlations in the sample matrix are due
    to sampling error.
    
    Kaiser-Meyer-Olkin Measure of Sampling Adequacy: is an index for
    comparing the magnitudes of the observed correlation coefficients to the
    magnitudes of the partial correlation coefficients.
    
    Large values for the KMO measure indicate that a factor analysis of the
    variables is a good idea.
    
                                90 or above, excelent
                                80 or above, meritorious
                                70 or above, middling
                                60 or above, mediocre
                                50 or above, miserable; and
                                below .50, unacceptable.

Examples

        . factortest price mpg rep78 rep77 hdroom rseat trunk


References

    Box,G.E.P.(1949) "A general distribution theory for a class of likelihood
        criteria." Biometrica, 36: 317-346.

    Cureton, E.E., & D'Agostino, R.B. (1983). Factor analysis: An applied
        approach. Hillsdale, NJ: Erlbaum.


Authors

    Joao Pedro Azevedo, IPEA, Brazil
    jazevedo@ipea.gov.br


Aknowledgements

    I would like to thank May M. Boggess for her help and Roberto De Miguel
        for his suggestions.


Also see

    Manual:  [R] factor [R] pca [R] alpha
    Online:  help for factor; pca; alpha