DUMC Library: EBM Glossary - R

  • Randomization (random allocation)
    Method analogous to tossing a coin to assign patients to treatment groups (the experimental treatment is assigned if the coin lands 'heads' and a conventional 'control' or placebo treatment is given if the coin lands 'tails').

  • Randomized control clinical trial (RCT)
    Study design where treatments, interventions, or enrollment into different study groups are assigned by random allocation rather than by conscious decisions of clinicians or patients. If the sample size is large enough, this study design avoids problems of bias and confounding variables by assuring that both known and unknown determinants of outcome are evenly distributed between treatment and control groups.

  • RCT -- see Randomized control clinical trial

  • Recall bias
    Systematic error due to the differences in accuracy or completeness of recall to memory of past events or experiences.

  • Referral filter bias
    The sequence of referrals that may lead patients from primary to tertiary centers raises the proportion of more severe or unusual cases, thus increasing the likelihood of adverse or unfavorable outcomes.

  • Relative Risk (RR, or Risk Ratio)
    The ratio of the probability of developing, in a specified period of time, an outcome among those receiving the treatment of interest or exposed to a risk factor, compared with the probability of developing the outcome if the risk factor or intervention is not present (i.e., the ratio of risk in the treated group to the risk in the control group: RR=EER/CER).

  • Relative Risk Reduction (RRR)
    The extent to which a treatment reduces a risk, in comparison with patients not receiving the treatment of interest (i.e., the percent reduction in events in treated compared to controls: RRR=[(CER-EER)/CER]).

  • Retrospective study
    Study design in which cases where individuals who had an outcome event in question are collected and analyzed after the outcomes have occurred.

  • Risk factor
    Patient characteristics or factors associated with an increased probability of developing a condition or disease in the first place. Compare with prognostic factors. Neither risk or prognostic factors necessarily imply a cause and effect relationship.

  • Risk ratio
    The ratio of risk in the treated group (EER) to the risk in the control group (CER). This is used in randomized trials and cohort studies and is calculated as EER/CER.

  • RR -- see Relative Risk

  • RRR -- see Relative Risk Reduction

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    Last modified on: 16-Dec-04