The prevalence of a disease in a population is defined as the proportion of people who are infected. Selection bias in disease prevalence estimates occurs if non-participation in testing is correlated with disease sta...The prevalence of a disease in a population is defined as the proportion of people who are infected. Selection bias in disease prevalence estimates occurs if non-participation in testing is correlated with disease status. Missing data are commonly encountered in most medical research. Unfortunately, they are often neglected or not properly handled during analytic procedures, and this may substantially bias the results of the study, reduce the study power, and lead to invalid conclusions. The goal of this study is to illustrate how to estimate prevalence in the presence of missing data. We consider a case where the variable of interest (response variable) is binary and some of the observations are missing and assume that all the covariates are fully observed. In most cases, the statistic of interest, when faced with binary data is the prevalence. We develop a two stage approach to improve the prevalence estimates;in the first stage, we use the logistic regression model to predict the missing binary observations and then in the second stage we recalculate the prevalence using the observed data and the imputed missing data. Such a model would be of great interest in research studies involving HIV/AIDS in which people usually refuse to donate blood for testing yet they are willing to provide other covariates. The prevalence estimation method is illustrated using simulated data and applied to HIV/AIDS data from the Kenya AIDS Indicator Survey, 2007.展开更多
Objectives To investigate the causes, theraputic and preventive methods of com- plications associated with transcatheter occlusion of at- rial septal defect ( ASD) using the Amplatzer septal oc- cluder (ASO) in childr...Objectives To investigate the causes, theraputic and preventive methods of com- plications associated with transcatheter occlusion of at- rial septal defect ( ASD) using the Amplatzer septal oc- cluder (ASO) in children. Methods 289 cases un- derwent transcatheter closure of ASD with ASO. Com- plications occurred in 9 cases. The complications in procedure included systemic circulatory systemic air embolism in 2, pulmonary air embolism in 1, pericar- dial tamponade in 1, ASO malposition requiring emer- gency surgical removal in 1, transient atrial extrasysto- les in 1 and sizing balloon rupture in 1 case. 2 cases with postoperative complications were found in the fol- low-up studies. These included perforation of mitral valve and ASO partially dislodged. In this study, 5 children with intraoperative complication received e- mergency therapy including surgical intervention, and others needed only follow-up, as the complications were transient or asymptomatic. Results There were no children death in this study. The 5 cases who re- ceived treatment were completely healing, and the oth- ers with intra - procedure complications were also had no sequela existed. Cases with mitral valve and ASO partially dislodged were still in follow-up studies, as the 2 patients having no symptoms. Conclutions Air embolism were occurred easily in atrial septal defect cases who received ASO therapy. Complications mainly caused by inappropriate operative procedure and some complications needed emergency treatments. Follow-up studies were important to cases with transcatheter oc- clusion therapy.展开更多
Based on the noise survey in China ,the formula (H=H+N-HN/120 ) of ISO/DIS 1999.2 (' Acoustics - Determination of Occupational noise exposure and estimation of noise induced hearing impairment ' , 1985) was ap...Based on the noise survey in China ,the formula (H=H+N-HN/120 ) of ISO/DIS 1999.2 (' Acoustics - Determination of Occupational noise exposure and estimation of noise induced hearing impairment ' , 1985) was applied to the calculation of the hearing threshold level associated with age and noise (HTLAN) of the noise - impaired people . According to the Gausscian distribution , when the noise - exposure level LEX8h was 85 ,90 ,95, 100 dB and the hearing threshold frequency is from 0.5k to 6kHz , the HTLAN of noise - exposed people withdifferent duration of exposure and its relation values to the hearing threshold frequency associated with age (HTLA) were obtained . The ISO /DIS 1999.2 has been proved to be applicable in China .展开更多
文摘The prevalence of a disease in a population is defined as the proportion of people who are infected. Selection bias in disease prevalence estimates occurs if non-participation in testing is correlated with disease status. Missing data are commonly encountered in most medical research. Unfortunately, they are often neglected or not properly handled during analytic procedures, and this may substantially bias the results of the study, reduce the study power, and lead to invalid conclusions. The goal of this study is to illustrate how to estimate prevalence in the presence of missing data. We consider a case where the variable of interest (response variable) is binary and some of the observations are missing and assume that all the covariates are fully observed. In most cases, the statistic of interest, when faced with binary data is the prevalence. We develop a two stage approach to improve the prevalence estimates;in the first stage, we use the logistic regression model to predict the missing binary observations and then in the second stage we recalculate the prevalence using the observed data and the imputed missing data. Such a model would be of great interest in research studies involving HIV/AIDS in which people usually refuse to donate blood for testing yet they are willing to provide other covariates. The prevalence estimation method is illustrated using simulated data and applied to HIV/AIDS data from the Kenya AIDS Indicator Survey, 2007.
文摘Objectives To investigate the causes, theraputic and preventive methods of com- plications associated with transcatheter occlusion of at- rial septal defect ( ASD) using the Amplatzer septal oc- cluder (ASO) in children. Methods 289 cases un- derwent transcatheter closure of ASD with ASO. Com- plications occurred in 9 cases. The complications in procedure included systemic circulatory systemic air embolism in 2, pulmonary air embolism in 1, pericar- dial tamponade in 1, ASO malposition requiring emer- gency surgical removal in 1, transient atrial extrasysto- les in 1 and sizing balloon rupture in 1 case. 2 cases with postoperative complications were found in the fol- low-up studies. These included perforation of mitral valve and ASO partially dislodged. In this study, 5 children with intraoperative complication received e- mergency therapy including surgical intervention, and others needed only follow-up, as the complications were transient or asymptomatic. Results There were no children death in this study. The 5 cases who re- ceived treatment were completely healing, and the oth- ers with intra - procedure complications were also had no sequela existed. Cases with mitral valve and ASO partially dislodged were still in follow-up studies, as the 2 patients having no symptoms. Conclutions Air embolism were occurred easily in atrial septal defect cases who received ASO therapy. Complications mainly caused by inappropriate operative procedure and some complications needed emergency treatments. Follow-up studies were important to cases with transcatheter oc- clusion therapy.
文摘Based on the noise survey in China ,the formula (H=H+N-HN/120 ) of ISO/DIS 1999.2 (' Acoustics - Determination of Occupational noise exposure and estimation of noise induced hearing impairment ' , 1985) was applied to the calculation of the hearing threshold level associated with age and noise (HTLAN) of the noise - impaired people . According to the Gausscian distribution , when the noise - exposure level LEX8h was 85 ,90 ,95, 100 dB and the hearing threshold frequency is from 0.5k to 6kHz , the HTLAN of noise - exposed people withdifferent duration of exposure and its relation values to the hearing threshold frequency associated with age (HTLA) were obtained . The ISO /DIS 1999.2 has been proved to be applicable in China .
