Cases were identified using a prediction model that estimates the probability of being treated for PD in a given year based on drug claims. The predictors include: cumulative dose or ever use between 1 January and 31 December of antiparkinsonian drugs (levodopa, dopamine agonists—pramipexole, ropinirole, pergolide, apomorphine, bromocriptine, lisuride—selegiline/rasagiline, piribedil, anticholinergics, catechol-O-methyl transferase inhibitors), proportion of the time treated, number of neurologist/general practitioner’s visits and sex. This model was validated against a gold standard (clinical examination), and we have previously shown this method to identify treated cases with a sensitivity of 92.5% and specificity of 86.4%.9 (link)
We first identified all persons with at least one antiparkinsonian drug reimbursement in 2009–2010 and excluded persons aged <20 years, women aged <50 years who were reimbursed for bromocriptine alone (lactation suppression), and persons only on anticholinergics and neuroleptics (drug-induced parkinsonism). We then applied the prediction model for the year 2010. Prevalent cases were persons predicted by the model as cases in 2010 and alive on 31 December 2010; incident cases were those persons predicted by the model as cases in 2010 who did not have antiparkinsonian drug reimbursements in 2009.
We used the sensitivity and specificity of the model to compute an overall corrected number of prevalent cases; this correction allows one to exclude false positives (eg, other causes of parkinsonism) and to correct for the imperfect sensitivity.10 (link) The corrected number of prevalent cases by sex and 5-year age groups was computed by assuming the same age and sex distributions for uncorrected and corrected numbers. The corrected number of incident cases was computed by assuming the same proportion of incident cases among all cases as for the uncorrected number of cases.
We first identified all persons with at least one antiparkinsonian drug reimbursement in 2009–2010 and excluded persons aged <20 years, women aged <50 years who were reimbursed for bromocriptine alone (lactation suppression), and persons only on anticholinergics and neuroleptics (drug-induced parkinsonism). We then applied the prediction model for the year 2010. Prevalent cases were persons predicted by the model as cases in 2010 and alive on 31 December 2010; incident cases were those persons predicted by the model as cases in 2010 who did not have antiparkinsonian drug reimbursements in 2009.
We used the sensitivity and specificity of the model to compute an overall corrected number of prevalent cases; this correction allows one to exclude false positives (eg, other causes of parkinsonism) and to correct for the imperfect sensitivity.10 (link) The corrected number of prevalent cases by sex and 5-year age groups was computed by assuming the same age and sex distributions for uncorrected and corrected numbers. The corrected number of incident cases was computed by assuming the same proportion of incident cases among all cases as for the uncorrected number of cases.
