Of the 979 patients, 623 (64%) returned 1–6 questionnaires (median 1, IQR 1–2) and the time interval from surgery to returned questionnaires ranged from 1.6 to 10.5 years (median 3, IQR 2.3–4.5). The questionnaire replies were sorted into groups, as shown in Table 3. All responses from the patients are included in the respective groups, except for two patients who replied twice during the same year; only one of these replies from each patient was included.Table 3Replies to questionnaire on long-term evaluation of 979 iNPH patients operated on in Sweden in 2004–2011. Available patients at each year after surgery were defined as living patients with follow-up within each time rangeGroupTime interval (years)Returned questionnaires (n)Proportion of available patients (%)Two years1.6–2.4929733Three years2.5–3.4924729Four years3.5–4.4915023Five years4.5–5.4914432Six years5.5–6.495617Seven years6.5–7.49188Eight years7.5–8.4921Nine years8.5–9.4944Ten years9.5–10.5513Total923Ever replying patients n = 623Proportion64%