Showing 7 results for Cohort Study
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.
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.
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.
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.
Zahra Gaeini, Sevda Alvirdizadeh, Parvin Mirmiran, Fereidoun Azizi,
Volume 20, Issue 2 (9-2024)
Abstract
Background and Objectives: The association between the consumption of dairy products and the risk of cardiovascular disease (CVD) is not well-known yet. Here, we aimed to determine the potential effects of total intake and subtypes of dairy products on the development of CVD in an Iranian adult population.
Methods: Among adult participants of the third phase of the Tehran Lipid and Glucose Study (TLGS), after excluding those with incomplete dietary, biochemical and anthropometric data, and those who had CVD events at baseline, 2635 adults were selected and followed up till the sixth phase of the TLGS. Baseline dietary intakes were evaluated using a validated food frequency questionnaire with 168 items. There was no significant difference between the baseline characteristics of participants who did not complete the FFQ and those of the total population in the third phase of the TLGS. Finally, the risk of CVD events after adjusting for potential confounding variables was evaluated across the tertile categories of dairy products using the Cox proportional hazard regression models.
Results: During a 10.6-year follow-up, the incidence rate of CVD was 6.5%. After adjusting for confounding factors, there was no significant association between CVD risk and total dairy, low-fat and high-fat dairy, fermented and non-fermented dairy products, high- and low-fat milk, high- and low-fat yogurt, cheese, and cream cheese, as well as ice cream.
Conclusion: According to numerous evidence in previous studies that revealed there is no association between the consumption of dairy products, and CVD risk, independent of high-fat or low-fat dairy products. Hence, it is vital to reconsider dietary recommendations on lowering the intake of high-fat dairy products for the prevention of CVD.
