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Time series analyses are often used to model a continuous response for all individuals at equally spaced time points. With the rapid advance of social network sites, network data are becoming increasingly available. The network vector autoregression (NAR) model incorporates the network information among individuals. The response of each individual can be explained by its lagged value, the average of its neighbors, and a set of node-specific covariates. However, all individuals are assumed to be homogeneous because they share the same autoregression coefficients. To express individual heterogeneity, we develop a grouped NAR (GNAR) model. Individuals in a network can be classified into different groups characterized by sets of parameters. The strict stationarity of the GNAR model is established. Two estimation procedures are developed, as well as the asymptotic properties of the proposed model. Numerical studies are conducted to evaluate the finite-sample performance of our proposed methodology. Lastly, two real-data examples are presented, based on studies on user posting behavior on the Sina Weibo platform and on air pollution patterns (especially PM2,5) in mainland China, respectively. [ABSTRACT FROM AUTHOR]

BACKGROUND: Pesticides have been associated with reproductive disorders, but there is limited research on pesticide exposures and human fertility. OBJECTIVE: We aimed to investigate the effects of preconception exposure to pesticides on time to pregnancy (TTP) and on infertility in a general population of couples planning to become pregnant in Shanghai, China. METHODS: A total of 615 women who were planning a pregnancy were enrolled before conception and were prospectively followed for 1 y to observe their TTP. Preconception pesticide exposures were assessed by measuring urinary metabolites of organophosphates (OPs) and pyrethroids (PYRs). Fecundability odds ratios (FORs) and odds ratios (ORs) of infertility were estimated using Cox and logistic regression models, respectively. All analyses were repeated after restricting the sample to nulliparous women (n=569). RESULTS: After adjusting for age, prepregnancy BMI, current smoking, education, annual household income, age at menarche, and two items from the Perceived Stress Scale (PSS-10), women in the highest quartile of diethylthiophosphate (DETP; an OP metabolite) had significantly longer TTP [adjusted FOR=0:68 (95% CI: 0.51, 0.92)] and increased infertility [adjusted OR=2:17 (95% CI: 1.19, 3.93)] compared with women in the lowest quartile. The highest versus lowest quartile of 3-phenoxybenzoic acid (3PBA; a PYR metabolite) was associated with longer TTP and infertility, with significant associations in nulliparous women [adjusted FOR=0:72 (95% CI: 0.53, 0.98); adjusted OR for infertility=2:03 (95% CI: 1.10, 3.74)]. CONCLUSION: Our study provides some of the first evidence that preconception OP and PYR exposures are associated with decreased fertility in Chinese couples. Given that OPs and PYRs are rapidly metabolized in humans, more studies are needed to confirm our findings. [ABSTRACT FROM AUTHOR]