title: Intraclass correlation and design effect in BMI, physical activity and diet: a cross-sectional study of 56 countries.
abstract: OBJECTIVE
  Measuring the intraclass correlation coefficient (ICC) and design effect (DE) may help to modify the public health interventions for body mass index (BMI), physical activity and diet according to geographic targeting of interventions in different countries. The purpose of this study was to quantify the level of clustering and DE in BMI, physical activity and diet in 56 low-income, middle-income and high-income countries.
  
  
  METHODS
  Cross-sectional study design.
  
  
  METHODS
  Multicountry national survey data.
  
  
  METHODS
  The World Health Survey (WHS), 2003, data were used to examine clustering in BMI, physical activity in metabolic equivalent of task (MET) and diet in fruits and vegetables intake (FVI) from low-income, middle-income and high-income countries. Multistage sampling in the WHS used geographical clusters as primary sampling units (PSU). These PSUs were used as a clustering or grouping variable in this analysis. Multilevel intercept only regression models were used to calculate the ICC and DE for each country.
  
  
  RESULTS
  The median ICC (0.039) and median DE (1.82) for BMI were low; however, FVI had a higher median ICC (0.189) and median DE (4.16). For MET, the median ICC was 0.141 and median DE was 4.59. In some countries, however, the ICC and DE for BMI were large. For instance, South Africa had the highest ICC (0.39) and DE (11.9) for BMI, whereas Uruguay had the highest ICC (0.434) for MET and Ethiopia had the highest ICC (0.471) for FVI.
  
  
  CONCLUSIONS
  This study shows that across a wide range of countries, there was low area level clustering for BMI, whereas MET and FVI showed high area level clustering. These results suggested that the country level clustering effect should be considered in developing preventive approaches for BMI, as well as improving physical activity and healthy diets for each country.
authors.affiliation: Department of Global Public Health, Jeffrey Cheah School of Medicine and Health Science, Monash University, Bandar Sunway, Malaysia Faculty of Dentistry, Center of Studies for Population Oral Health and Clinical Prevention, Universiti Teknologi MARA, Shah Alam, Malaysia.
authors.forename: Mohd
authors.initials: M
authors.lastname: Masood
authors.affiliation: Department of Global Public Health, Jeffrey Cheah School of Medicine and Health Science, Monash University, Bandar Sunway, Malaysia.
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Reidpath
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D016000:Cluster Analysis; D003430:Cross-Sectional Studies; D019049:Developed Countries; D003906:Developing Countries; D004032:Diet; D015444:Exercise; D005247:Feeding Behavior; D005260:Female; D006293:Health Promotion / Q000379:methods*; D006801:Humans; D007182:Income; D008297:Male; D055686:Metabolic Equivalent; D009043:Motor Activity; D009765:Obesity / Q000209:etiology / Q000517:prevention & control; D011203:Poverty; D011795:Surveys and Questionnaires
keywords: Body Mass Index (BMI); Intraclass correlation coefficient (ICC); Physical activity (METs)