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Case Series.  

Edward H. Livingston

in AMA Manual of Style: A Guide for Authors and Editors (11th edn)

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0017
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In a case series study, observations are made on a series of individuals, before and after they have received the same intervention, exposure, or diagnosis but have no control group. Case series describe characteristics of a group of patients or participants with a particular disease, disorder, signs, or symptoms or a group of patients or participants who have undergone a particular procedure or experienced a specific exposure or event. A case series may also examine larger units, such as groups of hospitals or municipalities. Case series can be useful to formulate a case definition of a disease or describe the experience of an individual or institution in treating a disease or performing a type of procedure. Case series should comprise consecutive patients or observations seen by the individual or institution to minimize ...

Case-Control Studies.  

Edward H. Livingston

in AMA Manual of Style: A Guide for Authors and Editors (11th edn)

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0015
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section
Case-control studies , which are always retrospective, compare those who have had an outcome or event ( cases ) with those who have not ( controls ). Cases and controls are then evaluated for exposure to various risk factors and thus should not be selected on the basis of their exposure to the risk factors under investigation. Cases and controls generally are matched according to specific characteristics (eg, age, sex, duration of disease) to reduce ...

Cohort Studies.  

Edward H. Livingston

in AMA Manual of Style: A Guide for Authors and Editors (11th edn)

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0014
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section
In a cohort study , a defined group of people (the cohort) is followed up over time to examine associations between different interventions and subsequent interventions. Cohort studies may be concurrent (prospective) or nonconcurrent (retrospective). A prospective cohort study follows up a group, or cohort , of individuals who are initially free of the outcome of interest. Individuals in a cohort generally share some underlying characteristic, such as age, sex, or exposure to a ...

Comparative Effectiveness Studies.  

Edward H. Livingston

in AMA Manual of Style: A Guide for Authors and Editors (11th edn)

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0018
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section
A comparative effectiveness study compares different interventions or strategies to prevent, diagnose, treat, and monitor health conditions to determine which work best for which patients and under what circumstances and which are associated with the greatest benefits and harms. Comparative effectiveness studies evaluate how effective existing therapies are in achieving various clinical outcomes. The outcomes may be tested by conducting RCTs or by observational analysis of existing data. Thus, from a study design perspective, they differ little from conventional studies of clinical efficacy....

Cross-sectional Studies.  

Edward H. Livingston

in AMA Manual of Style: A Guide for Authors and Editors (11th edn)

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0016
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section
Cross-sectional studies observe individuals at a single point or during a specific interval, in which exposure and outcome are ascertained simultaneously. Such studies may be helpful for suggesting associations among variables but cannot address whether one condition may precede or follow another. Thus, cross-sectional studies cannot establish ...

Ecologic Studies.  

Edward H. Livingston

in AMA Manual of Style: A Guide for Authors and Editors (11th edn)

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0025
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Ecologic studies examine groups or populations of patients but not the individuals themselves. They are useful for understanding disease prevalence or incidence and facilitating analysis of large numbers of people. These studies may uncover associations between exposure factors and diseases. Ecologic studies are limited by the ...

Economic Analyses.  

Edward H. Livingston

in AMA Manual of Style: A Guide for Authors and Editors (11th edn)

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Feb 2020
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Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0020
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Although a treatment or screening technique may be proven effective in an RCT, it still may not be clinically useful. Some interventions are prohibitively expensive, may benefit only a small fraction of a population, or may lead to significant downstream costs that preclude short-term savings or benefits....

Mediation Analysis.  

Edward H. Livingston

in AMA Manual of Style: A Guide for Authors and Editors (11th edn)

Print Publication Year: 
Feb 2020
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Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.2125
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In studies that use mediation analysis , the relationship between intervention and outcome is partitioned into indirect and direct effects or associations. These relationships are often shown in a diagram89 (see Figure 19.3-2). Mediation analysis can estimate indirect and direct relationships and the proportion mediated, a statistical measure estimating how much of the total intervention works through a particular mediator.The explicit objective of mediation analyses is to demonstrate potential causal relationships; however, this may not be possible and requires that specific assumptions be met. In a mediation analysis, the intervention-outcome, intervention-mediator, and mediator-outcome relationships must be unconfounded to permit valid causal inferences. In a randomized trial, participants are randomly assigned to intervention groups, so the intervention-outcome and intervention-mediator effects can be assumed to be unconfounded. However, trial participants are not usually randomly assigned to receive or not receive the mediator, so the mediator-outcome relationship may be confounded, even in randomized trials. To overcome this potential source of bias, investigators can control for known confounders of the mediator-outcome effect by using techniques such as regression adjustment. However, unmeasured confounding may still introduce bias even if known confounders have been adjusted for. Sensitivity analyses should be used to assess the potential bias caused by unmeasured confounding in mediation analyses. The risk of confounding in mediation analyses is greater in observational studies than in randomized trials, and in these cases, caution is required when interpreting findings and is best reported as interpreting estimates of indirect and direct associations....

Mendelian Randomization Studies.  

Edward H. Livingston

in AMA Manual of Style: A Guide for Authors and Editors (11th edn)

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0026
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Mendelian randomization uses genetic variants to determine whether an observational association between a risk factor and an outcome is consistent with a potential causal effect.90 , 91 Mendelian randomization relies on the natural, random assortment of genetic variants during meiosis, yielding a random distribution of genetic variants in a population. Individuals are naturally assigned at birth to inherit a genetic variant that affects a risk factor (eg, a gene variant that raises low-density lipoprotein cholesterol [LDL-C] levels) or not to inherit such a variant. Individuals who carry the variant and those who do not are then followed up for the development of an outcome of interest. Because these genetic variants may be unassociated with confounders, differences in the outcome between those who carry the variant and those who do not can be attributed to the difference in the risk factor. For example, a genetic variant associated with higher LDL-C levels that also is associated with a higher risk of coronary heart disease may provide supportive evidence to infer a potential causal effect of LDL-C on coronary heart disease....

Meta-analyses.  

Edward H. Livingston

in AMA Manual of Style: A Guide for Authors and Editors (11th edn)

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0019
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section
A meta-analysis is a systematic, statistical pooling of the results of 2 or more similar studies to address a question of interest or hypothesis. According to Moher and Olkin,50 [Meta-analyses] provide a systematic and explicit method for synthesizing evidence, a quantitative overall estimate (and CIs) derived from the individual studies, and early evidence as to the effectiveness of treatments, thus reducing the need for continued study. They also can address questions in specific subgroups that individual studies may not have examined....

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