van der Lende 2018.

Methods	Nested case‐control study in two epilepsy residential care facilities in the Netherlands and the UK
Participants	60 SUDEP cases under the age of 60 years, which occurred at two epilepsy residential care facilities in the Netherlands and the UK (Stichting Epilepsie Instellingen Nederland (SEIN) and Chalfont Centre for Epilepsy (CCE)) between 1987 and 2014. 4 controls per case were matched on age (±5 years) and residential unit, with the date of death of the SUDEP cases uses as an index date for matching controls. The cases were 42 males and 18 females, mean age 39.3 years. The controls were 132 males and 66 females, mean age 40 years.
Interventions	Nocturnal supervision was 1 of 5 listed as assessment variables between groups (see 'Outcomes' below for details of other factors not relevant to this review).
Outcomes	Association of case or control status with factors including nocturnal supervision. (Other factors not relevant to this review: having convulsive seizures, frequency of convulsive seizures, having nocturnal convulsive seizures, frequency of nocturnal convulsive seizures).
Notes	Characteristics of SUDEP cases and controls were mostly similar (epilepsy etiology, epilepsy duration, seizure types, number of antiepileptic drugs and use of benzodiazepines). However SUDEP cases had a higher frequency of convulsive seizures (P = 0.001), particularly nocturnal convulsive seizures (P < 0.001), and a higher intelligence quotient compared with controls (P = 0.005).
Risk of bias
Bias	Authors' judgement	Support for judgement
Bias due to confounding	Unclear risk	Moderate risk of bias: the objective of the study means that confounding is inevitable; however from the information available, it seems that confounders were measured fairly accurately and an appropriate adjusted analysis adjusting for convulsive seizure frequency (an important confounder) was performed.
Bias in selection of participants into the study	Unclear risk	Moderate risk of bias: unclear how many participants were reviewed when establishing SUDEP cases and exactly how matched controls were selected from the residential facilities. Unclear if any selection bias could have been present.
Bias in measurement of interventions	High risk	Serious risk of bias: likely that the 'grades of intervention' were defined for this study rather than at the start of the intervention, unclear whether the grades could have changed over time and it is possible that classification of the grade of intervention may have been affected by knowledge of case or control status.
Bias due to departures from intended interventions	High risk	Serious risk of bias: intervention of interest to us was not necessarily intended to be the only 'intervention' in the study. No information is given regarding adherence to the intervention, the consistency of the intervention and whether the 'grade' of the intervention could have changed over time and co‐interventions may have been present.
Bias due to missing data	Unclear risk	Moderate risk of bias: around 20% of included cases and controls were excluded from analysis due to missing data but as the amount of missing data is relatively small and balanced across cases and controls, it is unlikely conclusions would have been changed by this missing data.
Bias in measurement of outcomes	Unclear risk	Moderate risk of bias: objective outcome measurement, but unclear exactly how cases and controls were selected into the study and whether intervention status was determined after outcome status.
Bias in selection of the reported result	Unclear risk	Moderate risk of bias: results for 1 multivariable model reported, unclear if results would have been different for other multivariable models or if 'grade of intervention' could have been classified differently.

SUDEP: Sudden Unexpected Death in Epilepsy

Due to different options for the 'Risk of bias' judgement in the non‐randomised studies tool (Sterne 2016), we have assigned 'critical serious risk of bias' and 'serious risk of bias' as 'high risk of bias' and 'moderate risk of bias' as 'unclear risk of bias' in the table above. See the 'Support for judgement' column for more information and Table 3, Table 4, Table 5 and Table 6 for full quality assessments with signalling questions.