Interest in the presence and nature of trend arises frequently in science, public health, technology, and many other areas. In this article we discuss the notion of trend in the context of Recurrent event processes. We discuss different frameworks within which one can investigate trend and consider various ways in which trends may be manifest.Tests for trend are discussed in detail and the utility of intensity-based models is emphasized for characterizing event processes and understanding trends. Simulation studies are conducted to study the effect of heterogeneity in the investigation of trend. Data from a study of hospitalization patterns in patients with affective disorder are analysed for illustration.

Background: Restenosis after coronary angioplasty can have serious complications such as coronary artery bypass graft, myocardial infarction, and death. Objectives: The present study aimed at investigating the factors affecting the recurrence of coronary artery stenosis in patients undergoing angioplasty using the Recurrent event data analysis. Methods: A cohort study was performed on patients undergoing coronary angioplasty from March 23, 2009, to January 21, 2011. All patients were followed up from angioplasty to January 21, 2015. First, each of the independent variables was entered into the univariate Cox model with a frailty component. Then, variables with p-values of less than 0. 2 were entered into the multivariate analysis. The statistical analysis was done using R software, version 3. 6, at the significance level of 0. 05. Results: The present study was conducted on 1, 000 patients who underwent coronary angioplasty. We found that 441 patients experienced restenosis at least once in the study period. The mean survival time to the first event of restenosis was 44. 08 1. 06 months. Patients with a history of diabetes, unstable angina, and myocardial infarction had a significantly higher hazard of restenosis compared to other patients (P < 0. 05). Conclusions: The results of the Recurrent event survival analysis confirmed the significant role of risk factors such as a history of diabetes, unstable angina, and myocardial infarction. Therefore, training to enhance the patients’ awareness and attitude seems necessary to prevent them from exposing whit known risk factors. The periodic follow-up of patients with risk factors and more ongoing care are also necessary.

Background and Objectives: In many medical situations, people can experience Recurrent events with a terminal event. If the terminal event is considered a censor in this type of data, the assumption of independence in the analysis of survival data may be violated. This study was conducted to investigate joint modeling of frequent events and a final event (death) in breast cancer patients using a frailty model. Methods: In this retrospective cohort study, 443 patients with breast cancer registered at the Hospital of Shohadaye Tajrish Cancer Research Center were studied. The model of Liu (2004) was applied for joint modeling of Recurrent events and a terminal event in which a shared frailty with gamma-distribution was used. Data modeling and data analysis were done using the R software. Results: Four hundred and forty three women with breast cancer were studied. Univariate and multivariate analysis were performed in these patients. Of these, 338 cases (76. 3%) had recurrence events, and 105 (23. 7%) were censored. The obtained results of joint frailty model indicated that the relative risk of relapse in patients with a positive first-degree family history was 36% higher than that of other people (P<0. 05). The relative risk of relapse in patients with stage 3 disease was 19% more than other stages and also the relative risk of relapse in patients with chemotherapy was 2. 5 times higher than those without chemotherapy. Conclusion: In this study, the presented model, in addition to simultaneous modeling capability of the event, could help prevent a higher prevalence of the terminal event (death) and thus reduce the adverse effects of reversible diseases.

Background: Pemphigus is an autoimmune bullous disease and it is unclear what triggers and deteriorates it. The current study aimed to evaluate whether increasing the IgG antibody titer represents a good indicator of the pemphigus recurrence.Objectives: The current study aimed to evaluate whether increasing IgG titer is an indicator of the expected recurrence.Patients and Methods: The current study was conducted at the Department of Dermatology, Imam Khomeini Hospital, Tehran University of Medical Sciences, between March 2007 and December 2012. A total of 112 patients with confirmed diagnosis of pemphigus based on clinical, histological and immuno-histological criteria were engaged in the study. The primary outcomes of the study were Recurrent event times and IgG (Immunoglobulin G) antibody titer at each attendance. Joint model with shared random-effects was applied to assess the association between the two processes and investigate the affective factors.Results: Up to 8 recurrences were observed during the study time, but only 10% of the patients experienced more than 5 recurrences. A significant linear increasing trend in IgG antibody titer over time was found, IgG antibody titer increased 2.43% each month (P<0.0001). The results showed positive correlation between IgG antibody titer and recurrence of pemphigus (P<0.0001).Conclusions: The patients with higher IgG antibody titer were more likely to experience pemphigus recurrence. Therefore it can be concluded that titer of IgG and its increase may provide information regarding the progression of the pemphigus and the hazard of its recurrence.

Objectives: This study aims to examine the relationship between childbirth, abortions, and maternal death in determining maternal health. The research specifically focuses on the birth rate in Hamadan province.Methods: This retrospective cohort study considers birth and abortion as Recurrent events, with the times to birth, abortion, and maternal death as outcome measures. The parents' education level is also taken into account as a covariate. The rate of birth is estimated using a mixture cure frailty model, a bivariate joint frailty mixture cure model, and a multivariate joint frailty mixture cure model, depending on the presence of cure and terminal event.Results: A total of 633 mothers who gave birth to their first child in 2012 at Fatemiyeh Hospital in Hamadan participated in this study. The majority of couples (60.6%) had two children, and 526 (83.1%) had no abortions. The results show a significant decrease in the probability of childbirth among parents with an education level below a diploma (P-value < 0.05). Furthermore, the education level of mothers was found to have a significant impact on the birth rate. Specifically, having a diploma (Hazard Ratio = 0.826) or below a diploma (Hazard Ratio = 0.905) was associated with a lower rate of birth.Conclusion: The findings suggest a decline in the birth rate in Hamadan province over the past decade. Further research is needed to investigate the factors contributing to this decrease, taking into account the impact of abortions and maternal deaths on population growth.

event studies have found several applications in financial and accounting researches as the standard method to assess the average effect of some types of announcement on stock prices. In a large sample of announcements, event window length can be standardized (fixed) across observations, because the errors from having too long or too short event window should have small impact in average by the Law of Large Numbers. But in small samples (in emerging markets) we cannot use this procedure. Here, we examine various potential rules for determining the length of an event window when looking at limited number of observations. We consider the announcements of adjustment of predicted earnings (by companies) in Tehran Stock Exchange during 1386 to 1388. To determining the length of time period affecting the market, tree methods are used. We also examine the relationship between the length of event window and the amount of unexpected earnings.

Objective Seizure is the most common neurological disorder in pediatric medicine. This disorder is often chronic and requires continuous treatment. Developmental disorders are conditions that can occur due to abnormal development or damage to the brain and central nervous periods (outof-hospital). However, in most studies, the severity of seizure relapse is mistakenly considered the same for each period. The present study aimed to identify factors related to the recurrence of seizure in children with developmental disorder. Materials & Methods In this retrospective cohort study, 228 children with developmental disorder and a history of seizures referred to the emergency department of the Children’ s Hospital Medical Center in Tehran, Iran in 2016. Relapse times, admission duration and discharge time, age, sex, birth weight, type of delivery, parental relatives, maternal age during pregnancy, mother's history of medication use and disease during pregnancy, history of seizure with fever, family history of seizure, maternal delivery problems, length of pregnancy, history of admission to neonatal intensive care unit were recorded as factors affecting recurrence of seizure. Inclusion criteria were having developmental disorder and a history of seizure recurrence. The patients who were hospitalized for any reason other than seizure were excluded from the study. No intervention was performed in this study. Patients' information was recorded with their permission and based on ethical principles and the results were presented in the form of tables. Survival model was used to investigate the effect of risk factors on the seizure recurrence. If the seizure recurrence in children was controlled in hospital by medical staff, response variable (relapse time) was considered as censored. A frailty parameter was used to explain the correlation between recurrence of seizures in one subject, and a correlation parameter was used to justify the difference in in the rate of correlation between seizures in a hospital and in somewhere other than hospital. The collected data were analyzed using frailty model for Recurrent event by considering restraint period. To achieve an effective and flexible approximation for estimating base intensities, the piecewise constant intensity method was used. Estimation of the parameters was performed using the Gaussian quadrature method and by NLMIXED procedure in SAS V. 9. 2 software. Results Of 228 children, 125 (54. 8%) were boys and half of them were under 3 years of old. The mothers of 200 children (87. 72%) had age of 18-35 years at the time of pregnancy; 96 (41. 67%) of these patients were admitted to neonatal intensive care unit during neonatal period. The birth weight of 199 (28. 27%) children was about 2. 5-4 kg and 119 did not experience any seizure during the restraint period (in the hospital). The frequency of seizure recurrence in hospital ranged from 1 (25. 88%) to 16 times (0. 44%), while in out-of-hospital, it ranged from 1 (7. 46%) to 11 times (0. 44%). The duration of seizure recurrence was between 1 to 6196 days. Furthermore, children aged 1-2 years (P<0. 001) with a history of admission to neonatal intensive care unit (P<0. 001) whose mothers were 18-35 years of old during pregnancy (P=0. 022) experienced more out-of-hospital seizure recurrence, while children aged 1-2 years (P=0. 007) with a birth weight of 2. 5-4 kg (P= 0. 037) experienced less seizure recurrence in hospital. Conclusion Considering the meaningful relationships and appropriate planning, the recurrence of seizure can be reduced in children with developmental disorder during hospitalization or after withdrawal.

Background: Repeated events in cohort studies can be terminated by loss to follow-up, end-of-study, or a major failure event such as death or stable disease. In this regard, the major failure event can be correlated with Recurrent events, thus the usual assumption (no-informative censoring of the Recurrent event process by death) required by most statistical analyses, can be violated. Joint modeling as an appropriate way of analysis for this kind of data, can investigating two processes, simultaneously and leads to unbiased and efficient parameter estimations.Methods: In the present study, joint frailty model with maximum penalized likelihood method is introduced and used for analyzing real clinical data of cohort study was included first-degree relatives (FDR) of type 2 diabetes patients who attending to Isfahan endocrine and metabolism research center. The R-software (version 2.15.2) was used to fit the models.Findings: The hazard ratios adjusted by energy intake showed that pre-diabetes Recurrent rate is 3.48 times higher in Individual with carbohydrate greater than 65 percent energy intake, than Individual with lower than 40 percent energy intake. The hazards for terminal events as diabetes adjusted by energy intake indicated that the rate of diabetes 0.19 times higher in individual with protein 12-15 percent energy intake than individuals with protein lower than 12 percent energy intake and 0.19 times higher in individuals with protein greater than 15 percent energy intake than individual with protein lower than 12 percent energy intake.Conclusion: Adjusting life style through the nutritional status and anthropometric measure adjustments can effect on the prevalence of diabetes between FDRs who have genetics risk factors.