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Study Designs and Measures of Effect Size
Published in Mohamed M. Shoukri, Analysis of Correlated Data with SAS and R, 2018
A nested case-control study is within a cohort study. At the beginning of a cohort study, the time is t = 0. Thereafter, members of the cohort are assessed for risk factors. Cases and controls are identified subsequently at time t = 1. The control group is selected from the risk set (cohort members who do not meet the case definition at t = 1).
Sources of Data to Enable Benefit–Risk Assessment
Published in Qi Jiang, Weili He, Benefit-Risk Assessment Methods in Medical Product Development, 2017
Christy Chuang-Stein, George Quartey, Weili He, Qi Jiang, Haijun Ma, Jonathan Norton, John Scott, Jesse A. Berlin
The nested case–control study is something of a compromise between the cohort and case–control studies. In this setting, the cohort is established and defines the population from which both cases and controls are sampled (although often, a 100% sample of cases is taken). Because the cohort is defined, data collection took place before the cases became cases; hence, the temporality is the same as it would be under the cohort design. The efficiency is gained from having to get detailed information only for a sample of the noncases. Sampling of controls often uses a technique called incidence-density sampling, under which controls are sampled at the same point in follow-up as the corresponding matched case. For example, a case with the defining event after 2 years in the cohort would be matched with a control who has been in the cohort for at least 2 years and has not had the event. Information is collected from both the case and control over the same period, looking backward at exposures before that shared time point.
Observational Data Analysis
Published in Demissie Alemayehu, Joseph C. Cappelleri, Birol Emir, Kelly H. Zou, Statistical Topics in Health Economics and Outcomes Research, 2017
Demissie Alemayehu, Marc Berger, Vitalii Doban, Jack Mardekian
In a nested case-control study, which is a variation of the case-cohort design, controls are matched to the cases at the time of diagnosis (referred to as density sampling). Typically, one or more controls are selected for each case from subjects in the original cohort who are still at risk at the time a case is identified. Controls for a given case may later become cases after the time they are selected as controls. While such designs may be more susceptible to measurement error than cohort studies, one potential advantage in their favor is that controls are at risk for a comparable amount of time as the matched cases (Kleinbaum et al., 2013). However the analytical strategy should take into account aspects of the design, especially when subjects serve as their own control. In a purely self-controlled study, outcomes are compared before and after exposure in the same subject. An advantage of this design is that covariates that don’t vary within a person during the study period are automatically controlled. Typical analytical techniques under these conditions include conditional logistic and Poisson regression models, depending on the outcome measures (e.g., all occurrences versus only the first occurrence of an event).
Healthcare costs and outcomes associated with surgical site infections after coronary artery bypass grafting surgeries in Oman
Published in Annals of Medicine, 2023
Fatma M. AlRiyami, Omar M. Al-Rawajfah, Sulaiman Al Sabei, Hilal A. Al Sabti, Atika Khalaf
We implemented the nested case-control study design based on retrospective existing data, which was conducted from 2016 to 2017. All CABG patients within the study period constituted the study population. The data were collected from the two referral hospitals in Oman where all CABG surgeries are performed. Therefore, data from this study are generalizable to CABG surgeries in Oman. The inclusion criteria applied in this study were:Omani nationals >18 years old patients;Underwent CABG surgeries between 2016 and 2017 in the study hospitals. Patients who underwent CABG surgery more than once during the study period were counted as new case for each surgery; andHad electronic medical record in the study hospitals.
Nuts consumption and hypertension risks in children: a mediating role of circulating lipid metabolites
Published in Clinical and Experimental Hypertension, 2023
Liu Qin, Yanling Ren, Lan Chen, Ye Feng, Shunqing Luo, Ping Zhang, Wei Zhang, Xiaohua Liang
There are two strengths in our study. The first strength lies in its longitudinal design. We used a nested case–control study to minimize the potential effect of these confounding factors and obtain reliable results. In addition, we performed measurements and analyses of lipid metabolites to examine the effect that nuts may induce the change of lipids, and the lipids would impact blood pressure levels in children, which contributed to elucidate the underlying mechanisms linking nuts to lipid metabolism and hypertension. A further strength of the study was the fact that on three occasions blood pressure measurements were made to identify the hypertensive cases, which may reduce the number of false positive cases. Our study also has some limitations. First, as our sample size is relatively small, the power to detect the associations of nuts, lipids, and BP is limited after adjustment for multiple testing. Second, our findings were based on Chinese primary students without an available replication cohort to validate our lipidomic findings. Although, to our knowledge, these results are the first to link PG (43:6) to nut protective effect on BP, specific metabolic pathways involved in such a process, which have yet to be elucidated. It is essential to address these interactions and its regulatory mechanism in future study through a well-designed large sample size study.
The safety of metronidazole in pregnancy
Published in Health Care for Women International, 2021
Ozioma C. Nwosu, Kathaleen Bloom
The nested case-control study by Muanda et al. (2017) was appraised using the rapid critical appraisal of case control studies (Melnyk & Fineout-Overholt, 2015). Assessment of the validity examined how the cases were obtained and includes an examination of how the cases were selected and the appropriateness of the controls and data collection methods for cases and controls (Melnyk & Fineout-Overholt, 2015). The study was a nested one and this contributed positively to the validity of the study. All cases and controls were selected from the Quebec pregnancy cohort (1998-2000). The cases were pregnancies with a spontaneous abortion prior to the 20th week of gestation. Data were derived from medical records. Exposure was derived from pharmaceutical records as were antibiotic prescriptions overlapping with the index date. For all intents and purposes, the cases and controls were selected from the same population. Controls were randomly selected to ensure uniformity and each case was matched to ten controls. The use of data from medical records and registries decreased bias. The results were considered valid because of the methodology used and the results are judged to be reliable, as they are reflective of prior studies on the subject. The results also have high applicability, as antibiotics may be needed during pregnancy and knowledge is needed to guide the decision to prescribe them.