Objective

To compare the psychometric properties of scales top measure activities of daily living, constructed with different scaling methods, and to check whether the most complex scales have higher discriminatory capacity.

Method

Sample of elderly people from theSpanish Survey on Disability, Personal Autonomy and Dependency We used 14 items that measured activities of daily living. Five scaling methods were applied: Sum and Rasch (both for dichotomous and polytomous items) and Guttman (dichotomous). We evaluated the discriminatory capacity (relative precision [RP]) and area under the curve (AUC).

Results

All methods showed high Pearson correlations among them (0.765-0.993). They had similar discriminatory power when comparing extreme categories of individuals with no disability with severely limited (RP: 0.93-1.00). The polytomous Sum procedure showed the highest AUC (0.934; 95% confidence interval [95%CI]: 0.928-0.939) and Guttman the lowest (0.853; 95%CI: 0.845-0.861).

Conclusions

Polytomous items have greater reliability than the dichotomous ones. Simplest methods (Sum) and most complex (Rasch) are equally valid. Guttman method presented worse discriminatory capacity.

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