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Abstract.  

Edward H. Livingston

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

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Feb 2020
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Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0002
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Many readers will read only the abstract of a research article, so it should include as precise a summary of the content as possible. In addition, because readers may decide to review the entire article based on information in the abstract, it should be well written and carefully constructed....

Case Series.  

Edward H. Livingston

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

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Feb 2020
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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 ed.)

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Feb 2020
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Feb 2020
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10.1093/jama/9780190246556.003.0019.022.0015
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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 ...

Clinical Trials.  

Edward H. Livingston

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

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.021.0003
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The International Committee of Medical Journal Editors (ICMJE) defines a clinical trial as “any research project that prospectively assigns human participants to intervention, with or without concurrent comparison or control groups, to study the relationship between a health-related intervention and a health outcome.”6 All clinical trials must be registered at an appropriate online public registry. Interventions include but are not limited to drugs, surgical procedures, devices, behavioral treatments, educational programs, dietary interventions, quality improvement interventions, process-of-care changes, and the like....

Cluster Trials.  

Edward H. Livingston

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

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0011
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Cluster randomization is undertaken when performance of the intervention risks contamination of the control group. Imagine a multifaceted intervention that involves sedation protocols and measures of arousal levels and readiness for weaning from a mechanical ventilator in a trial of extubation.25 In this scenario, intensive care unit (ICU) personnel performing these functions may be influenced by the effectiveness of the interventions and consciously or unconsciously use them on patients assigned to the control group. In cases such as this, it is best to perform the intervention in one ICU and apply the control intervention in a separate ICU. Instead of randomizing individual patients to intervention or control groups, ICUs are randomized. Each ICU is considered a cluster of patients....

Cohort Studies.  

Edward H. Livingston

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

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10.1093/jama/9780190246556.003.0019.022.0014
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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 ed.)

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Feb 2020
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10.1093/jama/9780190246556.003.0019.022.0018
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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 ed.)

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10.1093/jama/9780190246556.003.0019.022.0016
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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 ...

Crossover Trials.  

Edward H. Livingston

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

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10.1093/jama/9780190246556.003.0019.022.0009
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In a crossover trial, participants receive more than 1 of the treatments under investigation, usually in a randomly determined sequence and with a prespecified amount of time (a washout period ) between sequential treatments. The participants and the investigators are generally blinded to the treatment assignment (double-blinded). This experimental design is often used for evaluating drug treatments. Each participant serves as his or her own control, thereby eliminating variability when comparing treatment effects and reducing the sample size needed to detect a statistically ...

Discussion.  

Edward H. Livingston

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

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Feb 2020
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10.1093/jama/9780190246556.003.0019.022.0006
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Authors should address whether the hypothesis was supported or refuted by the study results or how the study question was answered. The study result should be placed in the context of published literature. The limitations of the study should be discussed, especially possible sources of ...

Ecologic Studies.  

Edward H. Livingston

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

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Feb 2020
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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 ed.)

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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....

Equivalence Trials and Noninferiority Trials.  

Edward H. Livingston

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

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10.1093/jama/9780190246556.003.0019.022.0010
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It is sometimes desirable to compare a treatment or intervention that is already known to be effective with a treatment or intervention that is less expensive or has other advantages (eg, easier administration such as oral dosing).20 In these cases, it would be unethical to expose participants to an inactive ...

Glossary of Statistical Terms.  

Edward H. Livingston

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

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10.1093/jama/9780190246556.003.0019.021.0006
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In the glossary that follows, terms defined elsewhere in the glossary are displayed in boldface and italic font . An arrow (→) indicates points to consider in addition to the definition. For detailed discussion of these terms, the referenced texts and the additional reading at the end of the chapter are useful sources....

Introduction.  

Edward H. Livingston

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

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Feb 2020
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Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0003
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In the Introduction, briefly review the literature that documents the nature and importance of the research and rationale for the study. An extended full literature review belongs in the Discussion section. The study hypothesis or research question should be clearly stated in the last sentence(s) of the Introduction before the Methods section, preferably including the word ...

The Manuscript: Presenting Study Design, Rationale, and Statistical Analysis.  

Edward H. Livingston

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

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Feb 2020
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Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.021.0002
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Each portion of the manuscript should facilitate the reader’s understanding of why and how the study was done and (1) clearly state a hypothesis or study question, (2) show that the methods adequately answer the research question and that the data were appropriately analyzed, (3) convince the reader that the results are valid and credible, and (4) place the implications of the research in context and show that the study limitations do not preclude interpretation of the results....

Mediation Analysis.  

Edward H. Livingston

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

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Feb 2020
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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 ed.)

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Feb 2020
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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 ed.)

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Feb 2020
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Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0019
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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....

Methods.  

Edward H. Livingston

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

Print Publication Year: 
Feb 2020
Published Online: 
Feb 2020
DOI: 
10.1093/jama/9780190246556.003.0019.022.0004
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section
The Methods section should include enough information to enable a knowledgeable reader to replicate the study and, given the original data, verify the reported results. Analyses should follow the Enhancing the Quality and Transparency of Health Research (EQUATOR) Network reporting guidelines4 and be consistent with the study protocol and statistical analysis plan or described as post hoc. Components should include as many of the following as are applicable to the study design:...

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