Table 2.

Description of quality criteria

Unbiased randomised population sample (either from census list, or patient registers)

Adequate sample size (>1,000) (adapted from Loney and Stratford)[45]

Adequate response rate (>70%) (adapted from Loney and Stratford) [45]

Precise definition of NP provided (either written or drawing)

NP definition validated (either own validation or a reference)

Prevalence estimates with 95% CI provided (to estimate precision of data)

Analysis of non-responders (any comparison between responders and non-responders)

Each item was weighted equally and was given either 0 (criterion not fulfilled) or 1 (criterion fulfilled) point. Maximum score was seven points