JAMAevidence Glossary

Terms are derived from Users' Guides to the Medical Literature: A Manual for Evidence-Based Practice, 2nd Edition and The Rational Clinical Examination: Evidence-Based Clinical Diagnosis. Updated December 2009.
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P value
The probability that results as extreme as or more extreme than those observed would occur if the null hypothesis were true and the experiment were repeated over and over. A P value <0.05 means that there is a less than 1 in 20 probability that, on repeated performance of the experiment, the results as extreme as or more extreme than those observed would occur if the null hypothesis were true. See also Probability.

Palliate
Palliative care or treatment is a set of actions taken for patients in whom cure is unlikely. Stedman's defines palliative as mitigating or reducing the severity of symptoms without reducing the underlying disease. These actions are often multiple and can include family members and significant others.

Paracentesis
A surgical puncture of a bodily cavity with a trocar, aspirator, or other instrument usually to draw off an abnormal effusion for diagnostic or therapeutic purposes. Paracentesis can also be done as a therapeutic procedure when large volumes of fluid are removed to provide the patient relief from symptoms.

Parenchyma
The essential tissue of an organ or an abnormal growth as distinguished from its supportive framework.

Partial verification bias
Occurs when only a selected sample of patients who underwent the index test is verified by the reference standard, and that sample is dependent on the results of the test. For example, patients with suspected coronary artery disease whose exercise test results are positive may be more likely to undergo coronary angiography (the reference standard) than those whose exercise test results are negative. See also Bias.

Pastia sign
A scarlatiniform ("scarlet fever") rash in the antecubital fossae is one of the signs for streptococcal pharyngitis.

Patient expected event rate
The probability of the occurrence of the endpoint or outcome of interest in the patient group of which the individual under consideration is representative.

Patient preferences
The relative value that patients place on various health states. Preferences are determined by values, beliefs, and attitudes that patients bring to bear in considering what they will gain—or lose—as a result of a management decision. Explicit enumeration and balancing of benefits and risks that is central to evidence-based clinical practice brings the underlying value judgments involved in making management decisions into bold relief.

Patient-important outcomes
Outcomes that patients value directly. This is in contrast to surrogate, substitute, or physiologic outcomes that clinicians may consider important. One way of thinking about a patient-important outcome is that, were it to be the only thing that changed, patients would be willing to undergo a treatment with associated risk, cost, or inconvenience. This would be true of treatments that ameliorated symptoms or prevented morbidity or mortality. It would not be true of treatments that lowered blood pressure, improved cardiac output, improved bone density, or the like, without improving the quality or increasing the length of life.

Patient-mediated interventions
A strategy for changing clinician behavior. Any intervention aimed at changing the performance of health care professionals through interactions with, or information provided by or to, patients.

Pedigree
A diagram depicting heritable traits across 2 or more generations of a family.

Peek sign
A sign for myasthenia gravis elicited by having the patient close their eyelids to hold them in apposition. Despite effort to keep them closed, the lids gradually separate and the examiner will be able to see the sclera in a positive sign.

Per-protocol analysis
An analysis restricted to patients who adhered to their assigned treatment in a randomized trial (omitting patients who dropped out of the study or for other reasons did not actually receive the planned intervention). This analysis can provide a misleading estimate of effect because all patients randomized are no longer included, raising concerns about whether important unknown factors that influence outcome are equally distributed across comparison groups.

Performance criteria
Concerns how interventions are performed without regard to whether they should be performed. An example would be the acceptable range of results reported for reference cholesterol samples sent to clinical laboratories.

Periumbilical
Adjacent to the navel.

Phalen sign
Paresthesias in the distribution of the median nerve when the patient flexes both wrists 90 degrees for 60 seconds.

Phase I studies
Studies often conducted in normal volunteers that investigate a drug’s physiologic effect and evaluate whether it manifests unacceptable early toxicity.

Phase II studies
Initial studies on patients that provide preliminary evidence of possible drug effectiveness.

Phase III studies
Randomized controlled trials designed to test the magnitude of benefit and harm of a drug.

Phase IV studies
Studies conducted after the effectiveness of a drug has been established and the drug marketed, typically to establish the frequency of uncommon or unanticipated toxic effects.

Phenomenology
In qualitative research, an approach to inquiry that emphasizes the complexity of human experience and the need to understand the experience holistically as it is actually lived.

Phenotype
The observable characteristics of a cell or organism, usually being the result of the product coded by a gene (genotype).

Phi statistic (φ)
A measure of chance-independent agreement calculated by the following formula: [square root of (OR – 1)]/[square root of (OR + 1)].

PICO 
A method for answering clinical questions.

Placebo
A biologically inert substance (typically a pill or capsule) that is as similar as possible to the active intervention. Placebos are sometimes given to participants in the control arm of a drug trial to help ensure that the study is blinded.

Placebo effect
The impact of an intervention independent of its biological effect.

Point estimate
The single value that best represents the value of the population parameter.

Polymorphism
The existence of 2 or more variants of a gene, occurring in a population, with at least 1% frequency of the less common variant. See also Mutation.

Pooled estimate
Estimate based on combining data from 2 or more samples.

Population stratification
Describes the situation in which a population may be composed of multiple sub-groups of different ethnicity; case and control group differences in the mix can confound the comparison and lead to spurious genetic associations.

Positive predictive value
See Predictive value.

Positive study
1. A study with results that are consistent with the researchers’ hypotheses. 2. A study with results that show a difference that investigators interpret as beyond the play of chance.

Posttest odds
The odds of the target condition being present after the results of a diagnostic test are available.

Posttest probability
The probability of the target condition being present after the results of a diagnostic test are available.

Power
The ability of a study to reject a null hypothesis when it is false (and should be rejected). It is linked to the adequacy of the sample size: if a sample size is too small, the study will have insufficient power to detect differences between groups, if differences exist.

Pre-processed
A process whereby someone has reviewed the literature and chosen only the methodologically strongest studies.

Predictive value
Two categories: Positive predictive value—the proportion of people with a positive test result who have the disease; negative predictive value—the proportion of people with a negative test result and who are free of disease.

Pretest odds
The odds of the target condition being present before the results of a diagnostic test are available.

Pretest probability
The probability of the target condition being present before the results of a diagnostic test are available.

Prevalence
Proportion of persons affected with a particular disease at a specified time. Prevalence rates obtained from high-quality studies can inform pretest probabilities.

Prevent
A preventive maneuver is an action that decreases the risk of a future event or the threatened onset of disease. Primary prevention is designed to stop a condition from developing. Secondary prevention is designed to stop or slow progression of a disease or disorder when patients have a disease and are at risk for developing something related to their current disease. Often, secondary prevention is indistinguishable from treatment. An example of primary prevention is vaccination for pertussis. An example of secondary prevention is administration of an antiosteoporosis intervention to women with low bone density and evidence of a vertebral fracture to prevent subsequent fractures. An example of tertiary prevention is a rehabilitation program for patients experiencing the adverse effects associated with a myocardial infarction.

Primary care
Medical care provided by the clinician of first contact for the patient. Typically, the primary care physician is a general practitioner, family practitioner, primary care internist, or primary care pediatrician. Primary care may also be administered by health professionals other than physicians, notably specially trained nurses (nurse practitioners) and paramedics. Usually, a general practitioner, family practitioner, nurse practitioner, or paramedic provides only primary care services, but an individual with specialty qualifications may provide primary care, alone or in combination with referral services. Thus, it is the nature of the contact (first vs. referred) that determines the care designation rather than the qualifications of the practitioner. See also Referred care.

Primary care setting
Medical care facility that offers first contact health care only. Patients requiring specialized medical care are referred elsewhere. Some primary care centers provide a mixture of primary and referred care. Thus, it is the nature of the service provided (first contact) rather than the setting per se that distinguishes primary from more advanced levels of care. See also Primary care; Referred care; Tertiary care center.

Primary studies
Studies that collect original data. Primary studies are differentiated from synopses that summarize the results of individual primary studies and they are different from systematic reviews that summarize the results of a number of primary studies.

Probability
Quantitative estimate of the likelihood of a condition existing (as in diagnosis) or of subsequent events (such as in an intervention study). See also P value.

Prognosis
The possible consequences and outcomes of a disease and the frequency with which they can be expected to occur.

Prognostic factors
Patient or study participant characteristics that confer increased or decreased risk of a positive or adverse outcome.

Prognostic study
A study that enrolls patients at a point in time and follows them forward to determine the frequency and timing of subsequent events.

Provider adherence
Extent that health care providers carry out the host of diagnostic tests, monitoring equipment, interventional requirements, and other technical specifications that define optimal patient management.

Publication bias
Occurs when the publication of research depends on the direction of the study results and whether they are statistically significant. See also Bias.

Puddle sign
A maneuver to detect ascites that is not currently recommended. To elicit the finding, the patient must prop them selves up on their hands and knees, while the examiner reaches underneath the abdomen to percuss.

Pulmonary edema
Abnormal accumulation of fluid in the lungs.

Purposeful sampling
In qualitative research, a type of nonprobability sampling in which theory or personal judgment guide the selection of study participants who will be most representative of the population. Depending on the topic, examples include (1) maximum variation sampling, to document range or diversity; (2) extreme or deviant case sampling, in which one selects cases that are opposite in some way; (3) typical or representative case sampling, to describe and illustrate what is typical and common in terms of the phenomenon of interest; (4) critical sampling, to make a point dramatically; and (5) criterion sampling, in which all cases that meet some predetermined criteria of importance are studied.

Pyelonephritis
Bacterial or fungal invasion of the kidney causing tubular cell necrosis and inflammation of both the parenchyma and the lining of its renal pelvis. Chronic pyelonephritis involves pelvicaliceal inflammation, fibrosis, and deformity of the kidney.

Pyrexia
Abnormal elevation of body temperature, fever.

Pyuria
The presence of pus in urine.