Table 4.

Mean coverage of the 95% confidence interval by the true value over the three sample sizes for outcome Birthweight

	Death 4 covar.			Death 2 covar.			O2 dep. 4 covar			O2 dep 2 covar
Perc.	Random inter. var			Random inter. var			Random inter. var			Random inter. var
Twins	0.5	1	2	0.5	1	2	0.5	1	2	0.5	1	2
Logistic regression
2%	0.99	1.00	1.00	0.93	0.92	0.91	1.00	1.00	1.00	0.99	0.99	0.99
5%	0.99	1.00	1.00	0.95	0.94	0.94	1.00	1.00	1.00	0.99	0.99	0.99
10%	0.99	1.00	1.00	0.98	0.98	0.98	1.00	1.00	1.00	1.00	1.00	1.00
20%	0.99	1.00	1.00	0.99	0.98	0.98	1.00	1.00	1.00	1.00	1.00	1.00
Mixed logistic regression, PQL
2%	0.67	0.66	0.68	0.79	0.79	0.82	0.69	0.71	0.76	0.95	0.96	0.97
5%	0.59	0.58	0.58	0.91	0.91	0.92	0.76	0.79	0.85	1.00	1.00	0.99
10%	0.57	0.56	0.58	0.96	0.96	0.97	0.87	0.89	0.93	1.00	1.00	1.00
20%	0.56	0.55	0.60	0.99	0.99	0.99	0.95	0.96	0.97	1.00	1.00	1.00
Mixed logistic regression, Gauss-Hermite
2%	0.99	1.00	1.00	0.94	0.96	0.97	1.00	1.00	1.00	0.99	1.00	1.00
5%	0.98	0.99	0.99	0.94	0.96	0.98	1.00	1.00	1.00	0.99	1.00	1.00
10%	0.98	0.98	0.99	0.94	0.97	0.99	1.00	1.00	1.00	0.99	1.00	1.00
20%	0.97	0.97	0.98	0.95	0.98	0.99	1.00	1.00	1.00	0.99	1.00	1.00
GEE
2%	0.98	0.98	0.98	0.50	0.56	0.60	0.99	0.99	0.99	0.59	0.67	0.77
5%	0.98	0.98	0.98	0.54	0.63	0.68	1.00	1.00	1.00	0.66	0.76	0.86
10%	0.98	0.98	0.98	0.58	0.71	0.84	1.00	1.00	1.00	0.71	0.83	0.93
20%	0.98	0.98	0.98	0.65	0.80	0.92	1.00	1.00	1.00	0.78	0.90	0.97