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Objective: The generalized estimating equations (GEE) which is a method for estimating and belongs to the population average models is used in correlated data analysis. For the GEE method researcher must make guess for the working correlation structure. A related method to GEE is the quadratic inference functions (QIF). We aimed to compare two methods via an illustrative example and to estimate the relationship between sex, marital status, age, educational level, smoking status and obesity in participants who aged 20-65 years old. Material and Methods: This study compares two methods to estimate the odds of obesity (BMI ≥30 kg/m2) as a function of age, sex, marital status, educational level and smoking status by using data from" Tehran Lipid and Glucose Study (TLGS)" database which include 1106 households and 3203 participants aged 20-65 years. Results: The odds ratio estimates for two methods changed only slightly but the relative efficiency of parameter estimates from GEE and QIF was 1.23. QIF can produce sample size saving for a given power. Two methods showed that increased age, being a nonsmoker, lower educational level, and being married, as well as female sex were positively associated with obesity. Conclusion: According to the results of this study, QIF is better than GEE in the case of misspecification of the working correlation structure and provides more efficient parameter estimates than GEE method. [ABSTRACT FROM AUTHOR]

Background: We aimed to investigate the trend of childhood obesity in Tehranian population during a median follow-up of 10 years., Methods: Within a prospective cohort study, using data collected from Tehran Lipid and Glucose Study (TLGS), 1406 participants, aged 3-11 yr were selected and monitored in 4 phases: phase I (1999-2001), phase II (2002-2005), phase III (2006-2008) and phase IV (2009-2011)., Results: Total prevalence of obesity in children increased from 5.5% to 9.4% from phase I to IV. Performing GEE (Generalized Estimating Equation) analysis, relative risk of obesity was calculated, comparing each phase to its previous phase: phase II in reference to phase I (RR=1.06, CI=1.04-1.08), phase III in reference to phase II (RR=1.01, CI=1.00-1.03) and phase IV in reference to phase III (RR=0.96, CI=0.94-0.98). Between group difference was significant in all subgroups (age, gender, parental obesity) except parental education. Test of interaction for effect of time was insignificant in all subgroups except for the age group. For children younger than 7 yr old at phase I, trend of obesity throughout the study was higher compared to those with 7 yr of age and older at phase I., Conclusion: During a decade of follow-up, trend of obesity was rising in this Tehranian children in both genders, especially in younger children. Any preventive interventions for stopping this trend should focus on early stages of childhood., Competing Interests: Conflict of interest The authors declare that there is no conflict of interests., (Copyright© Iranian Public Health Association & Tehran University of Medical Sciences.)

Context: The prevalence of overweight and obesity are increasing worldwide and have frequently been associated with health risks. This review highlighted several studies regarding obesity, outlining contributions of over a span of almost two decades in the Tehran Lipid and Glucose Study (TLGS)., Evidence Acquisition: A systematic review was undertaken to retrieve articles related to all aspects of obesity from the earliest available date up to January 30, 2017., Results: Prevalence of excess weight, including overweight and obesity were 20.8 and 63.6% among those aged below and above 20 years, respectively. TLGS found a high incidence of obesity with higher incidence in women among Tehranian adults; the cumulative incidence of obesity was 31.3, 38.1 and 23.4% for the whole population, women, and men, respectively. In children and adolescents, younger non-obese 7 - 9 years old, compared to 10 - 11 year olds are at greater risk of obesity. Prevalences of abdominal obesity in men and women were 52.8% and 44.4% respectively. Similar to generalized obesity, a high incidence of abdominal obesity was observed; the total cumulative incidence of abdominal obesity was 76.0% (83.6% for men and 70.9% for women). Metabolically healthy obese (MHO) and metabolically healthy abdominal obese (MHAO) are two important obesity phenotypes. People with these phenotypes have different risks for cardiovascular disease (CVD), type 2 diabetes (T2DM), and mortality. In the TLGS participants, MHO was found in 2% and 7.7% of the whole and obese population, respectively, whereas MHAO phenotype was reported in 12.4% and 23.5% of the whole and abdominal obese population. In these unstable conditions, during the long term follow up the metabolic risks developed in nearly half of the individuals. During a 12-year follow-up, incident CVD did not increase in the MHO phenotype compared to metabolically healthy normal weight (MHNW) individuals, but the risk of CVD events had increased in all metabolically unhealthy phenotypes. However in another report, over a 10-year follow-up, MHAO phenotype had an increased risk for CVD in comparison to the reference group, metabolically healthy non-abdominal obese (MHNAO) individuals., Conclusions: The TLGS studies bridged the significant gap in knowledge regarding prevalence, incidence, trends, morbidities and mortalities for obesity among Iranian population.