Table 4

Zero inflation model of number of hospitalisations within a 10-year period of entering the study

Variable0 diseases (ref)Zero inflation model
Binary part*Count part†
OR95% CIP valueRisk ratio95% CIP value
Count of morbidities
1 disease0.73(0.67 to 0.80)<0.0011.24(1.18 to 1.31)<0.001
2 diseases0.57(0.52 to 0.63)<0.0011.53(1.45 to 1.62)<0.001
3 diseases0.51(0.45 to 0.58)<0.0011.70(1.59 to 1.80)<0.001
4+ diseases0.36(0.31 to 0.42)<0.0012.01(1.88 to 2.17)<0.001
SexFemales (ref)
Males1.03(0.99 to 1.07)0.05
AgeAge at entrance0.96(0.95 to 0.96)<0.0011.01(1.01 to 1.01)<0.001
EducationNo-education (ref)
Education1.22(1.13 to 1.31)<0.0010.95(0.91 to 0.99)0.01
Wealth quintilesWealth quintile 1 (ref)
Wealth quintile 20.89(0.82 to 0.97)0.007
Wealth quintile 30.89(0.82 to 0.96)0.003
Wealth quintile 40.86(0.80 to 0.94)<0.001
Wealth quintile 50.86(0.79 to 0.95)<0.001
EthnicityTurkmen (ref)
Not Turkmen0.76(0.70 to 0.81)<0.0011.15(1.11 to 1.20)<0.001
Smoking statusNever smoked (ref)
Current/ex-smoker0.86(0.79 to 0.94)<0.0011.07(1.02 to 1.12)0.001
BMIBMI <18.5 or ≥25 (ref)
BMI: 18.5≤x<251.16(1.08 to 1.24)<0.001
BMIBMI <25(ref)
BMI: ≥251.11(1.07 to 1.16)<0.001
Physical activityPhysical activity 1 (ref)
Physical activity 21.20(1.13 to 1.28)<0.001
Physical activity 31.24(1.15 to 1.35)<0.001
Physical activityPhysical activity 1–2 (ref)
Physical activity 30.93(0.89 to 0.97)<0.001
  • The following changes were made through backwards elimination.

  • Area of living and marital status were excluded from both models due to insignificance.

  • Sex was not a significant predictor of the outcome in the binary part of the model and was therefore excluded.

  • Wealth was not a significant predictor of the outcome in the count part of the model and was therefore excluded; BMI categories were changed to BMI 18.5–25 vs not for the binary part and <25 vs not for the count part.

  • Physical activity categories were changed to 1–2 vs 3 for the count part.

  • The zero inflation (binary) part shows ORs of how variables affect a participant being in the inflated zero-hospitalisations group, then a count model is fitted to show risk ratios for the number of hospitalisations which occur if a participant could have more than 0 hospitalisations.

  • *Predicting if a participant had certainly 0 hospitalisations in study period.

  • †Number of times of hospitalisations, if participant did not have certainly 0 hospitalisations.

  • BMI, body mass index.