Background and Aim: Case-Control studies provide evidence in the area of health. Validity and accuracy of such studies depend to a large extent on the similarity (similar distributions) of the case and control groups according to confounding variables. matching is a method for controlling or eliminating the effects of important confounders. matching using Propensity score has recently been introduced to control the effect of confounders, especially when there are many of them in a study. Materials and Methods: matching according to Propensity score was used in a genetic association study-a case-control study involving 300 subjects-to assess the effect of candidate genes on Alzheimer's disease in the Iranian population. Propensity score was calculated using STATA.8 software; age, sex, education level, job and genetic background were included in the model to calculate the score. Results: A total of 385 blood samples were taken from the participants. We managed to extract DNA in 155 of the 173 case subjects and in 161 of the 212 control subjects. The model for Propensity score was statistically significant. Of the total of 316 DNA samples, 302 were matched based on their calculated Propensity scores, while the individual matching method could only deliver 28 pairs.Conclusion: The Propensity-score matching method results in selection of a larger number of pairs, as compared with the conventional individual matching method. We propose to use this method, which also ensures a similar distribution of confounders between the case and control groups, particularly when there are limitations in the number of subjects available for matching.

Background: Many patients with mitral valve diseases need surgical procedures for the repair or replacement of their mitral valve. There is a great deal of controversy over the outcomes of the transseptal (TS) and left atrial (LA) approaches to the mitral valve. We sought to evaluate the outcomes of each approach more accurately by eliminating the possible biases in case selection and matching.Methods: This retrospective study included patients who had surgery for mitral valve diseases via either the TS approach or the LA approach between 2004 and 2011 in Tehran Heart Center. Patients with surgical approaches other than the TS and LA were excluded. To control for the confounding effects, a Propensity score matching technique was applied and the patients were matched for 14 demographic and preoperative variables. After the selection of controls, the effect of the TS approach (163 patients) versus the LA approach (652 patients) on the outcomes was presented through odds ratio (OR) with 95% confidence intervals (CI).Results: The mean age of the patients was 53.15 ± 12.02 years in the TS group and 52.93 ± 13.56 years in the LA group. Females comprised 119 (73.0%) patients in the TS group and 462 (70.9%) in the LA group. There was a significant association in the prevalence of new postoperative atrial fibrillation in the two groups (OR=1.539, 95%CI: 1.072-2.210; p value=0.019). Temporary pacemaker placement had no statistically significant difference between the two groups (p value =0.418). The TS patients had significantly longer pump (p value<0.001) and cross-clamp (p value<0.001) times. The mortality rate was 4.1% (27 patients) in the LA group and 6.1% (10 patients) in the TS group (p value=0.274).Conclusion: In our study population, the TS approach was associated with higher pump and cross-clamp times as well as risk of postoperative atrial fibrillation, but it did not increase the rates of permanent pacemaker placement, re-operations, and mortality.

Background: Brucellosis is the most widespread zoonosis worldwide and one of the most neglected zoonotic diseases. At present, large-scale farms are growing rapidly, increasing the risk of disease transmission. Objectives: In this study, the Propensity score matching (PSM) method was used to analyze the epidemiological characteristics of brucellosis and explore the risk factors of brucellosis infection in Hulunbuir, Inner Mongolia, China. Methods: A questionnaire for brucellosis was designed based on general knowledge and the protection of key groups of brucellosis. Epidata 13. 0 software was used to establish the questionnaire, and Propensity score matching was used to select cases that met the requirements of case-controls. Results: A total of 152 cases and 456 controls were included. The results of the study show that feeding livestock, carrying lambs regularly, and raising livestock without protective measures can increase the risk of brucellosis infection. Conclusions: Behavioral factors are the main risk factors for brucellosis, and livestock keepers should strengthen self-protection when working.

Background: The main task of the emergency medical system is to provide primary care and transfer the patients to hospital. Studies have been conducted to investigate the outcome of air and ground ambulance patients, but they show different results. These different results may be due to the type of study, statistical methods, differences in prehospital emergency systems, and insufficient control of confounding variables. Thus, it is difficult to compare and generalize the results. This study aimed to investigate the outcomes of injured people transported by air and ground ambulance in road traffic accidents in Qom Province, Iran, during 2015-2019. Materials and Methods: In this retrospective analytical descriptive study, we used the numerical method and examined all road traffic accident patients transferred through ground or air to Qom Shahid Beheshti Hospital by the prehospital emergency from 2015 to 2019. The collected information included the type of transfer, age, sex, type of trauma, distance from the accident site to the hospital, initial vital signs, duration of the mission, and day of the accident. To control the confounding factors, we used Propensity score matching. Outcomes studied included length of hospital stay, length of stay in the intensive care unit, duration of mechanical ventilation, and the need for immediate surgery. Logistic regression was used to analyze the need for immediate surgery and a generalized linear model for other consequences. Results: After matching, the number of patients in each group transferred by ground ambulances and helicopter was 566. Trauma to the head (P=0. 028) and back (P=0. 002) were more common in helicopter-transported patients. The patients transported by helicopter had a longer time to reach the scene (7. 70 ± 5. 18 min) (P<0. 001), a shorter duration of presence on the scene (12. 17± 8. 33 min) (P=0. 041), and a shorter duration of transfer (13. 12± 4. 75 min) (P<0. 001) than the ground ambulance. There was no significant difference between the patients who transferred by ground and helicopter ambulance regarding the length of hospital stay in the intensive care unit (P=0. 718), mechanical ventilation (P=0. 507), and hospitalization (P=0. 089). The need for immediate surgery in helicopter-transported patients was 84. 8% higher than ground ambulance patients (95%CI: 0. 086-0. 267; P<0. 001). Conclusion: The patients transported by helicopter were not significantly different from ground ambulances transported patients regarding staying in the intensive care unit, mechanical ventilation, and hospitalization, but they more needed immediate surgery. If the patients are triaged adequately according to the type of injury and the level of consciousness at the scene and transferred to the appropriate hospital by ground or air, they can enjoy the benefits of the type of transfer

The impact of global climate change warnings and ozone depletion on the global economy has attracted many researchers in recent decades, and many international organizations have taken action in response to these problems, including co-engagement Montreal, Kyoto, and Paris treaties. The purpose of this study was to investigate the relationship between the emission of some pollutants as an indicator of environmental pollution and macroeconomic variables such as energy consumption and foreign trade, and the effects of the obligations of member states in these treaties on the emissions of these pollutants. To this end, the matching approach has been used based on the desirability and regression of the difference-in-difference. The results of the alignment approach indicate a reduction in the emissions of carbon dioxide and total greenhouse gases for the Kyoto Protocol, and for the Montreal Treaty, the results of the alignment approach have contributed to the reduction of pollutants of hydro-fluorocarbons.

Background and Objectives: In most observational studies, researchers try to find causal relationships between observations. This correlation is associated with error due to lack of controlling confounding variables. One of the methods used to control the confounding variables is Propensity score matching. Therefore, the purpose of this study is to explain the steps of Propensity score matching. Materials and Methods: Propensity score matching has 5 steps. The first step is to estimate the Propensity score, which includes selecting the appropriate model and variables. The second step is to select an appropriate matching method based on the estimated Propensity scores. The third step is overlap and common support. At this stage, observations that are outside the range of matching scores are removed. The quality of the match is then evaluated, and finally the sensitivity of the estimated effects must be estimated. Results: In the Propensity score matching, the observed basic variables are balanced between the exposure and nonexposure groups. However, if the statistical model used to calculate the Propensity score is not correctly selected, an imbalance between the basic characteristics of the two groups can still exist. Conclusion: Propensity score matching is useful in cases where the confounding variables of study are high. In observational studies, this method can be used as an alternative to randomization in experimental studies, which makes the estimates more accurate by reducing the selection bias and controlling confounding variables.