DUMC Library: EBM Glossary - P

  • Patient Expected Event rate (PEER)
    This refers to the rate of events expected in a patient who received conventional therapy or no treatment.

  • PEER -- see Patient Expected Event Rate

  • Positive predictive value
    Proportion of people with a positive test who have the target disorder.

  • Post-test odds
    The odds that the patient has the target disorder after the test is carried out (calculated as the pre-test odds x likelihood ratio).

  • Predictive value
    In screening and diagnostic tests, the probability that a person with a positive test is a true positive (i.e., does have the disease), or that a person with a negative test truly does not have the disease. The predictive value of a screening test is determined by the sensitivity and specificity of the test, and by the prevalence of the condition for which the test is used.

  • Pre-test probability (prevalence)
    The proportion of people with the target disorder in the population at risk at a specific time (point prevalence) or time interval (period prevalence).

  • Prevalence
    The proportion of persons with a particular disease within a given population at a given time.

  • Prognostic factor
    Demographic, disease-specific, or co-morbid characteristics associated strongly enough with a condition's outcomes to predict accurately the eventual development of those outcomes. Compare with risk factors. Neither prognostic or risk factors necessarily imply a cause and effect relationship.

  • Prospective study
    Study design where one or more groups (cohorts) of individuals who have not yet had the outcome event in question are monitored for the number of such events which occur over time.

  • P-value
    The probability that the difference(s) observed between two or more groups in a study would occurred if there were no differences between the groups other than those created by random selection. Many researchers use a probability (p-value) of less than 0.05 as the cut-off for "statistical significance", i.e. when the sort of result seen in a study would occur by chance less than once in 20 studies.

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    Last modified on: 16-Dec-04