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Table 1 Estimates of prevalence (P), intracluster correlation coefficients (ICC), their respective 95% CI, design effect (Deff), and mean cluster size (n a ) for categorical maternal characteristics

From: Intracluster correlation coefficients for the Brazilian Multicenter Study on Preterm Birth (EMIP): methodological and practical implications

Variables P (%) ICC 95% CI for ICC Deff na
Skin color (white) 43.1 0.145 0.058-0.233 42.2 265
Marital status (with a partner) 77.7 0.008 <0.001-0.016 3.2 265
Schooling (>8 years) 60.5 0.030 0.008-0.053 10.6 261
Children under 5 years (≥1) 27.1 0.005 <0.001-0.011 2.4 265
Time since last delivery (until 12 months) 8.4 0.011 <0.001-0.022 2.8 155
Previous cerclage 1.1 0.001 <0.001-0.004 1.2 264
Previous preterm birth 17.3 0.007 <0.001-0.013 3.2 264
Previous preterm birth of multiples 1.0 <0.001 <0.001-0.003 1.2 264
Previous preterm labor 7.4 0.011 0.001-0.021 4.3 264
Previous prelabor PROM 7.2 0.002 <0.001-0.006 1.8 264
Previous indicated preterm birth 7.7 0.004 <0.001-0.009 2.0 263
Previous newborn weight < 2500 g 14.8 0.010 <0.001-0.019 4.1 262
Previous chronic diseases:
   Chronic hypertension 8.2 0.004 <0.001-0.009 2.4 265
   Diabetes mellitus 2.1 0.010 0.001-0.019 3.6 265
   Thyroid disease 1.8 0.012 0.002-0.023 4.4 265
   Cardiac disease 1.3 0.002 <0.001-0.005 1.4 265
   Lung disease 2.9 0.006 <0.001-0.012 2.8 265
   Renal disease 1.8 0.013 0.002-0.024 4.7 265
   Digestive disease 1.3 0.009 0.001-0.018 3.3 265
   Hematological disease 1.4 0.012 0.002-0.023 4.7 265
   Neurological disease 1.2 0.008 <0.001-0.016 3.7 265
   Psychiatric disease 1.4 0.022 0.005-0.038 7.0 265
   HIV 1.3 0.006 <0.001-0.012 2.6 265
   Other 6.5 0.033 0.009-0.057 11.8 265