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Evidence-based Practice in Healthcare

This guide is designed to assist health care professionals and students become effective and efficient users of the medical literature.

Definitions for Study Methodolgies

Case Control Studies [MeSH]* - Studies which start with the identification of persons with a disease of interest and a control (comparison, referent) group without the disease. The relationship of an attribute to the disease is examined by comparing diseased and non-diseased persons with regard to the frequency or levels of the attribute in each group.

Case Report (Study) [MeSH]* - A single, clinical presentation that may be followed by evaluative studies.

Case Series - Usually a coherent and consecutive set of cases of a disease (or similar problem) which derive from the practice of one or more health care professionals or health care settings.

Clinical Trial [MeSH]* - Work that is the report of a pre-planned clinical study of the safety, efficacy, or optimum dosage schedule of one or more diagnostic, therapeutic, or prophylactic drugs, devices, or techniques in humans selected according to predetermined criteria of eligibility and observed for predefined evidence of favorable and unfavorable effects. While most clinical trials concern humans, this publication type may be used for clinical veterinary articles meeting the requisites for humans. Specific headings for specific types and phases of clinical trials are also available.

Cohort Studies [MeSH]* - Studies in which subsets of a defined population are identified. These groups may or may not be exposed to factors hypothesized to influence the probability of the occurrence of a particular disease or other outcome. Cohorts are defined populations which, as a whole, are followed in an attempt to determine distinguishing subgroup characteristics.

Controlled Clinical Trial [MeSH]* - Work consisting of a clinical trial involving one or more test treatments, at least one control treatment, specified outcome measures for evaluating the studied intervention, and a bias-free method for assigning patients to the test treatment. The treatment may be drugs, devices, or procedures studied for diagnostic, therapeutic, or prophylactic effectiveness. Control measures include placebos, active medicine, no-treatment, dosage forms and regimens, historical comparisons, etc. When randomization using mathematical techniques, such as the use of a random numbers table, is employed to assign patients to test or control treatments, the trial is characterized as a RANDOMIZED CONTROLLED TRIAL.

Critically Appraised Topics (CATs) - A CAT is a short summary of the evidence to a focused clinical question.  It allows users to store the results of their critical appraisal in such a way that they can easily be shared or stored for later use.

Cross-sectional Study - The observation of a defined population at a single point in time or time interval. Exposure and outcome are determined simultaneously.

Follow-up Studies [MeSH]* - Studies in which individuals or populations are followed to assess the outcome of exposures, procedures, or effects of a characteristic, e.g., occurrence of disease.

Longitudinal Studies [MeSH]* - Studies in which variables relating to an individual or group of individuals are assessed over a period of time.

Meta-Analysis [MeSH]* - Works consisting of studies using a quantitative method of combining the results of independent studies (usually drawn from the published literature) and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc. It is often an overview of clinical trials. It is usually called a meta-analysis by the author or sponsoring body and should be differentiated from reviews of literature.

Practice Guideline [MeSH]* - Work consisting of a set of directions or principles to assist the health care practitioner with patient care decisions about appropriate diagnostic, therapeutic, or other clinical procedures for specific clinical circumstances. Practice guidelines may be developed by government agencies at any level, institutions, organizations such as professional societies or governing boards, or by the convening of expert panels. They can provide a foundation for assessing and evaluating the quality and effectiveness of health care in terms of measuring improved health, reduction of variation in services or procedures performed, and reduction of variation in outcomes of health care delivered.

Randomized Controlled Trial [MeSH]* - Work consisting of a clinical trial that involves at least one test treatment and one control treatment, concurrent enrollment and follow-up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process, such as the use of a random-numbers table.

Retrospective Cohort Study- starting with specific groups and looking at all of the past data to see if there was some sort of intervention and see how people have adapted overtime to present.

Systematic review - A summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies, and that uses appropriate statistical techniques to combine these valid studies.

*National Library of Medicine's Medical Subject Heading (MeSH) definition

Absolute Risk Reduction - The absolute arithmetic difference in rates of outcomes between experimental and control groups in a trial.

Bias - Prejudice or the lack of neutrality.  A systematic deviation from the truth that affects the conclusions and occurs in the process or design of the research.

Blinding - Process by which the participants and/or some of the researchers do not know the groups to which the participants have been assigned.

Co-intervention - Interventions other than the treatment under study that are applied differently to the treatment and control groups. his is a serious problem when double blinding is absent or when the use of very effective non-study treatments is permitted.

Confounder - A factor that distorts the true relationship of the study variables of interest by virtue of being related to the outcome of interest.

Confounding -A mixing of the effects within an experiment because the variables have not been sufficiently separated.  Possible confounding variables should be discussed in the report of the research.

Control Group - The group that does not receive the treatment, etc.

Decision Analysis - The application of explicit, quantitative methods that quantify prognoses, treatment effects, and patient values in order to analyze a decision under conditions of uncertainty.

Dependent variable - The component of an experiment that changes, or not, as a result of the independent variable (for example - the existence of a disease).

Hypothesis - A statement that is believed to be true but has not yet been tested.

Independent variable - The component of an experiment that is controlled by the researcher (for example - a new therapy).

Intention to treat analysis - A method of analysis for randomized trails in which all patients randomly assigned to one of the treatments groups is analyzed with the assigned group, regardless of whether or not they completed or received the treatment.

Loss to Follow-up/Intention to Treat - Research design concept that not all of the participants will complete the research study but that they should be accounted for even though they did not fully participate.

Number needed to treat (NNT) - The number of patients that we need to treat with a specific therapy in order to prevent one additional bad outcome. NNT can also be stated as the number of patients who must be treated for one patient to benefit. Calculated as the inverse of the absolute risk reduction 1/ARR.

P Value - The probability of any observed differences having happened by chance.  The convention is that .05 is required.   

Power - The likelihood that a study will detect a statistically significant difference.  The convention is that a power of at least 80% is required.

Randomization - Process that assigns participants by chance to either the treatment group or the control group.

*National Library of Medicine's Medical Subject Heading (MeSH) definition