[Analysis of the factors affecting survival of the kidney transplant patients by means of penalized splines model]

Background and Aim: Various methods are used to analyze the data in survival studies. The aim of this study was to compare the analysis results of penalized splines in Cox model and Cox proportional hazards model in relation to the effects of prognostic factors related to the survival of renal transplant patients

Material and Methods: This retrospective study included data of 876 renal transplant patients in Kermanshah, in Iran, from 2001 to 2015. Cox proportional hazards model and penalized splines in cox model were used. We used R version 3.3.2 for data analysis. The significance level was set at 0.05 and Akaike information criterion was used to compare the efficacy rates of these models

Results: Using Cox proportional hazards model, one, three and five year survival rates of the patients were 94.9, 92.3 and 90.2 percent, respectively. But the corresponding figures for penalized spline model were 95.6, 93.3 and 91.4 percent. The recipient's age, postoperative creatinine, urea after surgery and underlying diabetes were significantly associated with the patients' survival rates [p < 0.05]. Akaike's criteria for Cox proportional hazards model and penalized spline model were 1016.3 and 984.1, respectively

Conclusion: Considering lower Akaike information criterion and suitability of penalized spline model for continuous variables affecting the survival of renal transplant patients, this model can be used instead of Cox proportional hazards model for more accurate estimate of survival rate of the renal transplant patients

Investigating the impacts of retrofitted CNG vehicles on air pollutant emissions in Tehran

The present study was conducted to investigate the impacts of retrofitted CNG vehicles on air pollutant emissions in Tehran over a 20 years period using available statistical data, precise automobile tests, data analysis, and LEAP Software. The obtained results revealed an increase in air pollutant emissions including CO [equal to 1030.77 thousand tons], NO[x] [equal to 1030.77 thousand tons], THC [269.02 thousand tons] and CO[2] [equal to 38.43 thousand tons] resulting from utilizing retrofitted CNG vehicles within the studied period. Considering the obtained results, if the current trend of producing retrofitted CNG vehicles continues, a total cost of 435 million USD will impose on the environment, annually. According to the emission test results, by implementing retrofitted CNG vehicles policy, a higher emission rate of dual-fuel vehicles will be expected compared to their petrol-fueled counterparts. This is due to poor quality of the policy implementation such the use of substandard conversion kits and old technology of retrofit technologies