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Does more education mean less disability in people with dementia? A large cross-sectional study in Taiwan
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    Comment on statistics

    Poisson regression is unsuitable for analysing data from Likert scales, even in aggregate (see http://rcompanion.org/handbook/E_01.html).

    Summing enough Likert scales (as when summing enough random variables) might result in summary data which are suitable for least squares regression, via the central limit theorem. But, Poisson regression is suitable for count data where the variance is equal to the mean (count data that violate this equality may require negative binomial regression).

    Since the statistical analysis is inappropriate, the Results and Conclusions may be unsound.

    Multi-level IRT is probably an appropriate way to analyse multiple Likert scales (e.g. Luo & Wang, Stat Med. 2014 Oct 30; 33(24): 4279–4291)

    Conflict of Interest:
    None declared.