The factorial analysis of a quality of life scale for people addicted to drugs in methadone programs

Background: The evaluation scale of drug users Quality of life (QoL) in a substitution program with methadone, was developed with 21 items, twosubscales,“family and economic situation”(11 items) and“personalsatisfaction”(10 items) [1]. Concerning their reliability, in the valid-ation study for the Portuguese population in 2005 (n=236) was ob-tained an Alfa of Cronbach of 0.88 and in a recent study in2011(n=308) of 0.93 [1]. Objective: To determine a scale factorial structure and its psychometricproperties.Methods: Methodological study. Participants–180 drug users participated, agingan average of 41 years (SD=7.58 [24-69]), mostly men (73.3%), single(55.6%) and with children (52.8%), from 3 outpatients drug units. Dataanalyses - The correlation matrix of the items was evaluated throughexploratory and confirmatory factorial analysis. The factorial load as wellas the internal consistency estimated the dimensionality.Results: In the reliability analysis with 21 items was found an Alfa of Cron-bach of 0.89, all communalities >0.40, KMO=0.88 (p<0.001) and58.42% of explained variance by 5 factors. When extracted item 18(item-total correlation 0.16), all items assumed an item-total correl-ation > 0.20; alpha increased (α=0.90) and KMO increased to 0.88maintaining the stability of the Bartlett test; communalities main-tained above 0.40; total variance explained by the 5 factors increasedto 60.4%, but 5 factors diverged from theoretical matrix and 10 itemsweighed in more than one factor. Through confirmatory analysis (ex-cluding item 18) forcing for the 2 original scale factors, we verifiedthat 4 items had commonalities <0.30. The total variance explainedafter the spin fell to 43.11% and 4 items weighed in more than onefactor. We explored with 3 factors, KMO maintained in 0.88, Bartletttest remained within criteria, total variance explained after de rota-tion stayed 49.6%. Although this structure presents 3 items weigh inmore than one factor, justifies its maintenance by underlying the the-oretical model. Alpha is higher to initial (α=0.90). The extraction ofany item will weaken scale consistency. The most stable structurewas with 3 renamed factors: 1- Personal satisfaction and self-care (8items) (38.5% explained variance); Social Family situation (8 items)(7.4%); 3- Socio professional and economic situation (4 items) (6.5%).The fidelity of the scale is reinforced by the internal consistency ofits subscales, factor 1α=0.85; factor 2α=0.79; factor 3α=0.72 and bythe correlation between them (0.51-0.67; p<0.01). Conclusions: Good internal consistency. Factorial analysis supported by the theor-etical matrix. Good discriminant capacity by differences pointed outin some variables.