Table 1 Percentages of missing values (minimum, maximum) for each of the three groups of variables (predictor variables, covariates and outcome variables).

	Predictor variables	Covariates	Outcome variables
Finland	0%; 16.6%	0%; 8.1%	0%; 31.7%
Denmark	0%; 14.0%	0%; 12.8%	0%; 29.9%
Netherlands	0%; 11.3%	0%; 16.8%	0%; 19.6%
United Kingdom	0%; 10.3%	0%; 18.7%	0%; 20.3%
Spain	0%; 11.4%	0%; 25.7%	0%; 20.1%
Portugal	0%; 7.6%	0%; 21.5%	0%; 14.6%