Missing data plagues almost all surveys and researches. The occurrence of missing data will cause losses of original sample information and undermine the validity of the research results to some extents, so researchers should attach great importance to this problem. In this article, we introduced 3 kinds of missingness mechanism, namely missing completely at random, missing at random, and not missing at random. We summarized some common approaches to deal with missing data, including deletion, weighting approach, imputation and parameter likelihood method. Since these methods had its pros and cons , we should carefully select the proper way to handle missing data according to the missingness mechanism.

Objective: To explore the relationship between prenatal anxiety and cesarean section (c-section) with non-medical indication.
Methods: Nested case-control study was used to analyze the risk factors for c-section with no medical needs: 433 pregnant women with gestational age longer than 24 weeks were enroled in this study. According to the mode of delivery, we divided them into a vaginal delivery group, a c-section group without medical need and a c-section group with medical need.
Results: The c-section rate was 62.1%, 55.8% of which was c-section without medical need at family request. The score of state anxiety (S-AI) and trait anxiety (T-AI) was 42.53±11.04 and
44.40±10.23 respectively, much higher than that of normal population. After the adjustment of maternal social economic status and other prenatal statuses for this pregnancy, the prenatal anxiety was still associated with c-section with non-medical indication. The adjusted odd ratio for prenatal anxiety state, prenatal trait anxiety state and c-section with non-medical indication was 1.41 (95%CI: 1.06-1.87) and 1.23 (95% CI: 1.08-1.40), respectively.
Conclusion: Prenatal anxiety state is a risk factor for c-section with non-medical indication.

Objective:To explore the incidence of PTSD and its risk factors among adults in flood district.Methods:Diagnostic and Statistical Manual of Mental Disorders(Ⅳ Edition) were used to examine and diagnose the victims.Results:The positive rate of PTSD was 33.8%.The results of logistic regression analysis showed that style of flood (OR=4.07),having been besieged by the flood when waiting for resue(OR=2.65),seeing other people drowned by flood(OR=2.77),having the experience of staying with the dead in flood(OR=3.14) and level of satisfaction with sustaining(OR=0.72) were risk factors.Conclusion:PTSD is a not uncommon mental disorder among adults in flood district in our country and psychosocial intervention is needed.

Objectives To know the affecting degree of snail status by the flood in schistosomiasis epdemic areas.Methods The eight embankments suffered from disasterous floods and collapsed were selected in Dongting Lake; the changes of snail states and snail-killed etc.Before and after disasterous floods were surveyed by retrospectively. Results In the eight embankments, the snail areas inside embankment increased at different degree except two embankments where snail was not found after disaster, it was 10.8 times of that before disaster; Furthermore, after disaster the snail was found in the embankment enclosing village areas inside where it was not found before disaster; in most of embankments collapsed, the mean density of living snail inside embankment and mean density of infected snail and positive rates of snail outside embankment descended at different degree after disaster. Conclusions Inside embankment, the disastrous floods could lead to snails speading in most of embankments collapsed. Otherwise, outside embankment the flood led to reduce the mean density of infected snail and positive rates of snail in most of embankments collapsed, and the degree of snails spreading was affected by the factors such as the snail states at the collapsed place, mean density of living snail,immersed area by water, mud and sand ect.

Objective In order to explore the incidence of PTSD and its risk factors after flood. Methods Diagnostic and Statistical Manual of Mental Disorders (Ⅳ Edition) was used to examine and diagnose the victims in flood district. Results The positive rate of PTSD was 30 9%.The results of logistic regression analysis showed that sex(OR=2 32), age (OR=1 83),style of flood (OR=3 71)and dissatisfaction for sustaining (OR=0 84)were risk factors. Conclusions PTSD is a common mental disorder after flood in our country. Preventive measures should be taken to protect population from PTSD in flood district.

Objective:To explore the prognosis of posttraumatic stress disorder (PTSD) in flood survivors 13 years after they had been diagnosed with PTSD symptoms,and investigate the relationship between their personality traits and the prognosis of PTSD.Method:In this cross-sectional study,the survivors of Dongting Lake flood in 1998-1999 in Hunan in China,who were investigated and screened as PTSD symptoms positive in 2000 were selected as the target population,from which a sample of 200subjects was drawn using amulti-stage random sampling method.The Posttraumatic Stress Disorder Scale Civilian Version (PCL-C) was used to examine and re-screen the participants of PTSD symptoms in order to explore the prognosis of PTSD.Participants whose PCL-C scores were equal to 44 or higher were classified as the PTSD symptoms positive group,while those with PCL-C scores less than 44 were classified as the recovered group.Personality traits were then assessed,using the Revised Eysenck Personality Questionnaire Short Scale for Chinese (EPQ-RSC),in both the recovered group and the PTSD symptoms positive group.Finally,the multivariate logistic regression analysis was used to investigate the relationship between the prognosis of PTSD and personality traits.Results:Totally 200 subjects were eligible for this study and completed the questionnaires,but 16 of them had their questionnaires excluded from data analysis because they provided incomplete information.Thus,the response rate was 92.0％.According to the PCL-C's cut-off score,22 participants were still screened as PTSD symptoms positive and were classified as the PTSD symptoms positive group,whereas the other 162 participants were screened as PTSD symptoms negative and were classified as the recovered group.Compared with the recovered group,the EPQ-RSC extroversion scores for the PTSD symptoms positive group were significantly lower [(51.8 ± 10.7) vs.(45.1 ± 13.2),P ＜ 0.05] and their neuroticism scores were significantly higher [(46.5 ± 10.1) vs.(58.3 ± 12.2),P ＜ 0.05].The multivariate logistic regression analysis showed,after adjusting for the variables such as gender and age,that higher neuroticism (OR ＝ 3.63,95％ CI:1.05 -12.54) was a risk factor for the persistent PTSD symptoms in the flood survivors.Conclusions:It suggests that neuroticism is associated with prognosis of PTSD in flood survivors,those with higher neuroticism scores appear to have problems to recover from PTSD.

Objective: To investigate the blood lead level (BLL) in painters and the inlfuential factors, and to provide the theory foundation for the prevention and control of lead poisoning in painters. Methods: A total of 535 painters from Sany Heavy Industry Company Limited and Xiangjiang Kansai Paint Corporation, who participated in the health examination during October 2012 and December 2012, were recruited and divided into a positive blood lead group and a negative blood lead group according to the level of blood lead. Questionnaires survey and physical/biochemical examinations were performed. Chi-square Test and multivariate logistic regression were used to estimate the factors that contributed to the elevated blood lead. Results: hTe results from 525 questionnaires and physical/ biochemical examination were collected. There were 55 workers (10.4%) whose BLL were 0.04 mg/L. The maximum value of BLLs was 0.35mg/L. hTe multivariate logistic regression showed that smoking (OR=2.424), smoking or eating in the workplace (OR=2.139), not washing hands before smoking or eating (OR=1.624), and the cycle of changing masks longer than two weeks (OR=2.158) were positively associated with BLL. Conclusion: Smoking, smoking or eating in the workplace, not washing hands before smoking or eating, and the cycle of changing masks longer than two weeks are risk factors for higher BLL.

Objective To understand the current distribution and characteristics of advanced schistosomiasis patients who accepted medical assistance in Hunan Province in 2015,so as to provide the evidence for perfecting the policy and measures of the medical assistance to advanced schistosomiasis patients. Methods The patients who had been diagnosed as advanced schis-tosomiasis were verified and confirmed according to the standard of the medical assistance to advanced schistosomiasis patients in Hunan Province in 2015. The epidemiological survey was conducted to investigate the demographic characteristics,history of diagnosis and treatment,and medical assistance to these persons. Results There were 3850 advanced schistosomiasis patients who accepted the medical assistance in Hunan Province in 2015,and among them,2664 patients were male(69.19%),and 1186 were female(30.81%). Most of them(92.82%)came from the main schistosomiasis endemic areas,such as Yueyang, Changde and Yiyang. There were 2369 cases of ascites(61.53%),1466 cases of splenomegaly(38.08%),15 cases of colon proliferation and dwarf(0.39%). The mean age of advanced schistosomiasis patients who accepted the medical assistance was (62.94 ± 11.67)years old,with 64.31% of them being more than 60 years old. The age of initial diagnosis of advanced schistoso-miasis was(53.85 ± 21.32)years old,and it was concentrated in 40-60 years old(68.57%). The mean duration of advanced schistosomiasis was(9.58 ± 10.06)years,and it was mainly distributed in 10 years(75.95%). The mean duration from initial diagnosis of schistosomiasis to advanced schistosomiasis was(22.33 ± 14.20)years. The priority of the medical assistance to ad-vanced schistosomiasis patients was given to the county hospitals(76.57%);and the effective rate of assistance was 94.46%. To-tally 86.57% of the patients with advanced schistosomiasis got the medical insurance(rural cooperative medical care,urban medical care,etc.). Conclusions The burden of the medical assistance to advanced schistosomiasis patients is still heavy be-cause of many patients and low cure rate in Hunan Province. The ascites patients and high age patients should be the important objects of the medical assistance.

As a metabolic disorder during pregnancy,gestational diabetes mellitus (GDM) has an important effects on fetal development,neonatal health and maternal long-term health,and is one of the pregnancy complications with high incidence.It is of great significance that we have an accurate understanding of the etiology and risk factors of GDM for its prevention and control.GDM is a complex disease with multiple etiologies.Current studies have shown that the occurrence of GDM may be the result of combined effect of heredity and environment,but the exact etiology is still unclear.In this paper,we summarized the possible etiologies and risk factors of GDM,so as to understand the occurrence and development of GDM better and to provide possible references for prevention and further etiological studies of GDM.

Objective To determine the prevalence and the risk factors for childhood obesity in Changsha and Shenzhen, China.Methods A case-control study was conducted in 209 obese children (the cases) identified in the investigation on childhood obesity in 6 288 children aged 6 to 9 years in Changsha and Shenzhen in China and 209 children with normal weight (the controls). The cases and controls were matched by gender, age, and school. Adjusted odds ratio (aOR) and 95% confidence intervals (CI) for the risk factors were measured.Results The prevalence rate of overweight and obese children was 9.28% and 3.30% in Changsha, and 12.17% and 4.22% in Shenzhen, respectively. The rate of overweight children is significantly higher in Shenzhen than in Changsha. No statistical difference was observed in the rate of obesity between the children in both cities. Paternal obesity (OR 1.78, 95% CI 1.01 to 3.16), maternal weight gain during pregnancy ≥15.0 kg (OR 5.22, 95% CI 2.78 to 9.80), birth weight ≥4.00 kg (OR 2.55, 95% CI 1.24 to 5.26), unhealthy snacks ≥1 per week (OR 3.94, 95% CI 1.11 to 13.99), and watching television ≥2 hours per day(OR 2.35, 95% CI 1.01 to 5.47) were associated with childhood obesity when potential confounding factors were adjusted by multi-variable logistic regression analysis. Conclusion Paternal obesity, gestational weight gain, high birth weight, and unhealthy life-style are important risk factors for obesity in urban children in south China.