The diagnostic method has a strong influence on classification of XXXX .

@entity1 @entity26 @entity27
Polygraphy (PG) and polysomnography (PSG) are used in clinical settings in Europe for diagnosing @entity27 ( @entity27 ), but their equivalence in unselected clinical cohorts is unknown. We hypothesized that the method would affect both diagnostic outcomes and disease severity stratification. Data from 11  049 @entity1 in the multi-centre European Sleep Apnea Cohort (ESADA) with suspected @entity27 (male and female, aged 18-80  years) were used in two groups of @entity1 to compare PG (n  =  5745) and PSG (n  =  5304). Respiratory events were scored using the 2007 American Association of Sleep Medicine (AASM) criteria. In subjects who underwent PSG, mean @entity27 index (AHI) using sleep time (AHIPSG 31.0      26.1  h(-1) ) and total analysed time (TAT) (AHITAT 24.7      22.0  h(-1) ) were higher than in subjects who underwent PG (AHIPG 22.0      23.5  h(-1) ) (P  <  0.0001). The @entity26 desaturation index (ODI) was lower in subjects investigated with PG (ODIPG 18.4      21.7  h(-1) ) compared to subjects investigated with PSG (ODIPSG 23.0      25.3  h(-1) ) but not different when the PSG was indexed by TAT (ODITAT 18.6      21.4  h(-1) , P  <  0.65). The proportion of @entity1 with an AHI >=   15 was 64% in the subjects who underwent PSG and 47% in the subjects who underwent PG (P  <  0.001). Overall, @entity1 investigated using PG are likely to have a 30% lower AHI on average, compared to @entity1 investigated by PSG. This study suggests that PG interpreted using standard guidelines results in underdiagnosis and misclassification of @entity27 . We advocate the development of PG-specific guidelines for the management of @entity27 @entity1 .
