Showing 13 results for Cohort
R Chaman, A Shamshiri, K Kamali, Ghr Khalili, K Holakouie Naieni,
Volume 2, Issue 1 (3-2006)
Abstract
Background & Objectives: This investigation was prompted by the growing importance of nested case-control studies and the increasing frequency with which they are done in epidemiologic research. After a brief explanation of nested case-control studies, we evaluate the trends in research methodology over the last decade, especially with regard to cohort, case-control, and nested case-control designs.
Methods: Data for this study were extracted from the PubMed database, using these keywords: Nested Case-Control, Risk-Set Sampling and Density Sampling. The search was confined to the 10-year period from 1996 to the end of 2005. As for other methodologies, we used keywords Cohort and Case-Control for a search over the same time period. The search itself was performed on April 25, 2006.
Results: We found 2011 articles reporting nested case-control studies. There were 95 such articles in 1996 the number had increased to 289 in 2005. Case-control and cohort designs accounted for 68456 and 60479 articles, respectively.
The number of case-control articles rose from 4378 in 1996 to 10270 in 2005, while that of cohort articles increased from 2981 to 9771 over the same period.
Conclusions: The number of cohort and nested case-control articles followed similar upward trends over the last decade and their rate of increase was greater than that of simple case-control articles.
J Poorolajal, P Tajik, B Yazdizadeh, M Sehat, Ar Salehi, M Rezaei, K Holakouie Naieni,
Volume 5, Issue 1 (6-2009)
Abstract
Background & Objectives: Observational studies are not often reported in detail and clear enough, so that assessment of the strengths and weaknesses of these studies is not straightforward. To improve the reporting of observational studies, a checklist of items called ‘Strengthening the Reporting of Observational Studies in Epidemiology’ (STROBE) was developed by some experts in October 2007. The aim of this study was to assess the quality of reporting of observational studies before STROBE statement.
Methods: We included randomly sixty cohort studies published in six important international journals until October 2007. Then, we used STROBE checklist to assess the strengths and weaknesses of these included studies.
Results: On average, more than 81% (95% CI: 77%-87%) of included studies pointed to 43 items of aim of this study. The most reported (100%) items were "scientific background" and "rationale for the investigation" and the less reported (30%) item was “flow chart”.
Conclusions: Although, the quality of reported cohort studies’ results was acceptable, the type of study, journal and date of publication could influence on the quality of observational studies.
M Moradi Lakeh, M Montazer, M Moradi, Smh Mahmoodi, Sap Alemzadeh Bahreini, S Askari,
Volume 5, Issue 3 (12-2009)
Abstract
Background & objectives: The trend of stunting indicates of long term health status and the efficacy of different health interventions for chronic malnutrition in children. The objective of this study was to investigate the trends of stunting prevalence in preschool children living in rural area of Robat-Karim.
Methods: The method of Age-Period-Cohort analysis was utilized. Existing height data of all children whom registered in health houses of Robat-Karim health network were converted to Standard Deviation Scores (SDS) using Anthro2005 software The SDS≤ -2 for height-for-age was defined to be the moderate/severe forms of stunting. Age-Period-Cohort analysis was done with two graphical and statistical methods. The statistical method was based on logistic regression modeling in which stunting was assumed to be the dependent variable and age, birth cohort and time period were independent variables.
Results: Growth data of 970 (51.9%) boys and 898 (48.1%) girls were analyzed. The overall stunting prevalence was estimated 8.0%. This estimation by Logistic regression models (P<0.001) and graphical analyses were similar and showed that the prevalence of stunting has a decreasing trend in different birth cohorts and time periods. The prevalence of stunting was higher in the 2nd and 5th-6th years of life. The stunting prevalence was significantly higher in boys (9.3%) and non-Iranian children (9.5%) (P<0.001).
Conclusions: The prevalence of stunting appears to be decreasing in the investigated population. Appropriate interventions is thought to be essential for reducing stunting of 2nd and 5th-6th years of life, boys, and non-Iranian children.
K Holakouie Naieni, A Ostovar, A Danesh, S Sadjedinejad, L Ghalichee, Gh Moradi, Ma Mansournia, Ss Hashemi Nazari,
Volume 6, Issue 2 (9-2010)
Abstract
Background and objective: The nested case-control study has become popular as an efficient alternative to the full-cohort design. This study compares the results of a nested case-control analysis approach with the full cohort analysis.
Methods: A cohort of 276 subjects (new cases from a TB registry) was used for this study. Cox Regression model was used for the full cohort analysis. In order to do the nested case-control analysis, for each death, three random controls were selected from those who did not suffer from the outcome at the time of the outcome took place. Case control data was analyzed by the conditional logistic regression model.
Results: Results from both cohort and nested case-control analyses show that treatment group is the only variable that affects on the outcome. Gender, place of residence, and age has no effect on the outcome. For binary exposure variables with trivial effects (e.g. Gender and place of residence), the relative efficiency of nested case-control study design is approximately 75%.
Conclusion: Results of this study show that nested case-control study is not only an easy and cost-effective method for data analysis but also is as robust as cohort analysis in rate ratio and its variance estimation.
Ab Mohammadian Hafshejani, H Baradaran, N Sarrafzadegan, M Asadi Lari, A Ramezani, Sh Hosseini, F Allahbakhshi Hafshejani,
Volume 8, Issue 2 (9-2012)
Abstract
Background & Objectives: Despite decreasing the trend of coronary artery
diseases in developed countries and outstanding improvements in clinical
management of these patients, case fatality rate after an acute myocardial
infarction (AMI) remains high in both genders. Identifying predicting factors
of short-term survival in patients with AMI may play an important role in
reducing mortality in these patients.
Methods: In
this cohort study, all patients with acute myocardial infarction (AMI) admitted
to all hospitals in Isfahan, Iran, during 2000-2008 which registered in Isfahan
cardiovascular research Institute were analyzed. We used Cox regression models,
uni- and multi-variable analysis.
Results: Within
the study period, 8800 AMI patients (73.6% male) were admitted with mean age of
61.85±12.5, and overall 28-day survival of 90.5%. Relative risk (RR) of death
for 50-70 years old patients was 2.5 (CI:2-3.1), for over 70 years old RR=5
(CI:4-6.3), for women RR=1.7 (CI:1.5-1.9), for patients who had not received
streptokinase RR=0.9 (CI:0.8-1.1), for inferior MI RR=4.2 (CI:2.2-7.8) and for
anterior MI, RR was equal to 7.2 (CI:4-13.3).
Conclusion: Recognizing
the predicting factors of short-term survival of AMI patients may help health
professionals to provide better healthcare services for more at risk patients,
i.e. elderly, women and patients with an anterior MI.
M Nazarzadeh, D Khalili, B Eshrati, F Hadaegh, F Azizi,
Volume 9, Issue 4 (3-2014)
Abstract
Background & Objectives: The case-cohort study is one of the youngest designs in epidemiology and some methodological aspects of it are still in debate. This study aimed at comparing the estimated hazard ratio, standard error, and interaction hazard ratio between the case-cohort and cohort studies for assessing the relationship between diabetes and cardiovascular diseases.
Methods: A total of 1701 men and 2253 women aged between 40 and 75 years were considered as the main cohort. Subcohort sampling was performed using simple random sampling with a sampling fraction of 0.3%. The hazard ratio of the cohort study was calculated using Cox regression model and the 3 methods of Prentice, Self-Prentice, and Barlow were used for calculating the hazard ratio of the case-cohort study. The mentioned regression models were used to assess the interactions.
Results: The results of the two studies were similar in populations with higher incidence (cohort of men) and lower incidence (the cohort of women) when frequency percent of exposure variable was greater than 10%. When the sample size of the initial cohort was less than 1250 subjects, discrepancies were observed between the results of the two studies. In addition, the standard error of the case-cohort study was higher than the cohort study. The results of both studies were similar in assessing the considered interactions.
Conclusion: The results are similar when the initial cohort sample sizes are sufficient. Meanwhile, unlike the percentage of exposure frequency, the outcome incidence has a negligible impact on the discrepancy between the results while the effect of the relative frequency of the exposure levels on the results discrepancy is noticeable.
A Motevalian, R Sahebi, A Rahimi Movaghar , M Yunesian,
Volume 11, Issue 2 (9-2015)
Abstract
Background & Objectives: The aim of the study was to determine age, period, and cohort effects on trend of alcohol and drug use in the students of Tehran University of Medical Sciences from 2006 to 2009.
Methods: Between 2006 and 2009, the students of Tehran University of Medical Sciences were surveyed annually using a structured self-administered and anonymous questionnaire. Intrinsic estimator, which is a new method for resolving linear dependency between age, period, and cohort in linear regression models, was used for data analysis.
Results: In the present study, in the descriptive method, the prevalence of alcohol consumption increased in males and females with an increase in age. The prevalence of illicit drug use was higher in 2007 in comparison with other periods for males and females. In the analytical method (intrinsic estimator), there were no age, period and cohort effects for alcohol and drug use for females. For males, the age effect exhibited an increasing-decreasing-increasing trend and period and cohort effects showed a decreasing trend for alcohol use. As for drug use, the age effect exhibited gradual increases. The period effect displayed an increasing-decreasing trend and the cohort effect exhibited an increasing-decreasing-increasing trend.
Conclusion: The IE method showed no age, period and cohort effects for alcohol and drug use in females. The prevalence of drug and alcohol use increased with an increase in age in males. The high prevalence of drug use could be due to easy accessibility and low price of drugs.
K Holakouie Naieni , Ma Mansournia, Mh Panahi, A Elduma, Sh Nematollahi ,
Volume 12, Issue 3 (10-2016)
Abstract
Case-Cohort and nested case-control designs are the most well-known and cost-effective derivatives of prospective studies. Due to the popularity of these designs in recent years, the aim of this study is to provide a comprehensive and up-to-date description of them with respect to methodological issues such as sampling scheme, effect measure estimation, and analysis strategies. Overall, random sampling of controls in case-cohort and matching for time in nested design are considered their hallmarks. Eventually, decision on a better design depends on study objectives, sub-cohort selection, case and control determination, and method of data collection. It should be kept in mind that any particular study requires unique elaboration and delicate examination to choose from the designs.
R Sahebi, Sa Motevalian, L Sahebi, H Sharifi,
Volume 13, Issue 2 (9-2017)
Abstract
Background and Objectives: The aim of this study was to compare the intrinsic estimator method and the age, period and cohort accounting model used for identifying age, period, and cohort trends in incidence, prevalence, and mortality rates.
Methods: The data of 2 studies " Age, Period, and Cohort Effects on Alcohol and Drug use Among Students of Tehran University of Medical Sciences from 2006 to 2009" and "The Role of Age, Period, and Cohort Effects on Smoking among the Students of Tehran University of Medical Science "were used. First the age, period and cohort accounting model and then The IE method are explained, their advantages and disadvantages are discussed, and their results are compared.
Results: Both methods showed an increasing, decreasing, and increasing trend for age, cohort, and cohort effect for the prevalence of smoking. IE could predict a preventing effect for an early age factor for smoking. In the descriptive model, a decreasing trend was seen from old cohorts to younger cohorts in nearly all age groups. However, the IE method did not show any cohort effects for alcohol consumption in female studnets.
Conclusion: Currently, the IE method is the best method for solving linear dependence between three variables of age, birth cohort, and period in this type of studies. However, researchers should use it with caution because it has many pitfalls.
S Ebrahimi Kebria , Ss Hashemi Nazari, Y Mdehrabi, B Nazparvar , A Shojaei, Sd Mirtorabi,
Volume 15, Issue 1 (5-2019)
Abstract
Background and Objectives: Suicide is one of the psychosocial problems in Lorestan Province due to its socio-cultural and economic structure. The aim of this study was to investigate the effect of age group, time period, and birth cohort on the suicide incidence in Lorestan Province during the 2006-2015.
Methods: In this study, to overcome the identifiability problem, the Carstensen approach and natural cubic smoothing character were used in age-period-cohort models (APC). Cohort effect was calculated as the relative rate from the 1984 reference cohort for men and 1987 cohort for women. The period effect in both sexes constrained to be relative to 1390 and to be 0 on average with 0 slope. The best APC model for both sexes was the models with "AC-P" parameter, 7 knots, and natural splines for men and B splines for women. All analyses were performed using the R software with Epi package.
Results: The age effect showed that the highest suicide incidence rate was seen in the elderly. Two strong birth cohort effects were observed, one increasing one in the 1980 cohort and one decreasing one in 1991 cohort. The most significant period effect was seen in men in 2011.
Conclusion: The effects of 1991 and 1980 birth cohorts could be due to the consequences of imposed war in Iran. The three economic phenomena, oil price change, increased divorce rate, and increased unemployment rate can be effective in the emergence of the period effect in year 2011.
R Bayrami, R Latifnejad Roudsari ,
Volume 16, Issue 3 (11-2020)
Abstract
Background and Objectives: The results of cohort studies could be used in evidence-based medicine in case they have a good quality and robust methodology. Therefore, this study was conducted to assess the quality of cohort studies investigating preconception risk factors of gestational diabetes.
Methods: In this cross-sectional study, the cohort studies investigating the preconception risk factors of gestational diabetes during 2008-2018 indexed in PubMed, Scopus and Science Direct were searched. Keywords used for search included cohort study, pre pregnancy, preconception, risk factor and gestational diabetes. Out of 312 retrieved articles, 26 were critically appraised using the STROBE checklist. The maximum and minimum score that each article could obtain was 34 and 0, respectively. Data were analyzed using SPSS version 16.
Results: Of 26 articles that were reviewed, the overall agreement rate with STROBE was 78.8%. Of these, 18 articles (69/23%) were rated as moderate and eight articles (30.76%) were graded as good quality. The method and result sections were the weakest parts of the published articles.
Conclusion: The quality of the reported cohort studies investigating preconception risk factors of gestational diabetes is not optimal. It is recommended that chief editors, reviewers, and authors as well as obstetricians and midwives use the STROBE criteria to appraise articles critically, before using their findings in clinical practice.
K Holakoui-Naeini, Ma Mansournia, Sh Naderian, R Beiranvand, M Bidkhori, Kh Maajani, Sh Nematollahi,
Volume 17, Issue 2 (9-2021)
Abstract
Background and Objectives: Pre-natal mental health problems are major causes of disease burden, especially in lower socio-economic groups of population. The present study used data of a prospective cohort study to estimate the risk of mental health problems, including depression, anxiety, and stress, on birth weight.
Materials and Methods: This study used data of 398 pregnant women who were participants of the Bandar Abbas Pregnancy Cohort Study (BAPC) during 2017-2020. Data of depression, anxiety, and stress were collected using DASS-21items questionnaire in pregnancy. Low Birth Weight (LBW), as birthwieght below 2500 grams, was calculated according to infant`s vaccination log. Modified Poisson regression models with logarithm link function and significance level of 5% were applied to estimate the effect of depression, anxiety and stress on LBW.
Results: Compared to the subjects without mental health problems, the risk of LBW increased by 8.03 times in the severe depression (95% CIs: 5.55-11.62), by 8.06 times in the moderate stress (95% CIs: 5.64-11.51), by 3.13 times in the severe anxiety (95% CIs: 1.18-8.31), and by 8.43 in the highly severe anxiety (95% CIs: 5.80-12.25).
Conclusions: Severe and moderate levels of depression, anxiety, and stress all had statistically significant effects on LBW. Pre-natal screening services can help mitigate the burden of mental health by timely detection and referral. Moreover, designing and implementing consultation programs for pregnant women and their fsmilies, expecially their spouses, to provide emotional support and to improve marital relationship are amongst the suggestions.
Mohsen Mahdinia, Seyyed Hassan Adeli, Hamidreza Heidari, Abolfazl Mohammadbeigi, Mohammadreza Khaksar, Ahmad Soltanzadeh,
Volume 17, Issue 2 (9-2021)
Abstract
Background and Objectives: Pulmonary consequences of exposure to low concentrations of ammonia have been less studied. The purpose of this study was to model the pulmonary consequences of exposure to low concentrations of ammonia.
Methods: This historical cohort study was conducted in the fertilizer industries in 2019. The participants were divided into two groups of exposed (n=98) and non-exposed (n=105). The exposure level, pulmonary symptoms, and pulmonary function parameters were assessed using the NMAM 6016 and American Thoracic Society and European Respiratory society (ATS&ERS) protocols. Data analysis was performed using the IBM SPSS v. 22.0, and multivariate linear and logistic regression models.
Results: The ammonia exposure level was 4.80±1.54 ppm in the exposed group. There was no significant difference in most of the individual variables between the two groups (P>0.05). The frequency of all pulmonary symptoms was significantly higher in the exposed group compared to the non-exposed group (P<0.05). The highest prevalence of pulmonary symptoms in the exposed group was for cough (25.51%), wheezing (19.39%) and shortness of breath (18.37%). All lung function parameters were significantly lower in the exposed group versus the non-exposed group (P<0.05). The values of lung function parameters in the exposed group including FVC, FEV1 and FEV1 / FVC were 86.0%, 82.47% and 81.97%, respectively. Regression modeling results showed that ammonia exposure had a significant relationship with all pulmonary symptoms and lung function parameters (P<0.05).
Conclusion: The findings indicated that exposure to low concentrations of ammonia should be considered as a major risk factor in the prevalence of pulmonary symptoms and reduced lung function parameters.
