**A B C D E
F G H I J K
L M N O
P Q R S T U
V** W X Y Z

**Evidence Based Medicine:** when best evidence from research
meets clinical information and patient values, optimal decisions are
possible.

**Absolute risk**: The observed or calculated
probability of an event in the population under study.

(*Harm/Etiology,
Therapy*)

**Absolute risk difference**: The difference in the risk
for disease or death between an exposed population and an unexposed population.
(*Harm/Etiology*)

**Absolute risk reduction**
**(ARR)**: the difference in the absolute risk (rates of adverse
events) between study and control populations. (*Therapy*)

**Adjustment**:
A summarizing procedure in which the effects of differences in composition of
the populations being compared have been minimized by statistical methods. See
Confounding variable (*Harm/Etiology*)

**ARR **: see
Absolute risk reduction

**Bias (systematic error)**: Deviation of results or
inferences from the truth, or processes leading to such deviation.

See also Referral bias,
Selection bias, Verification bias.

(*Harm/Etiology,
Therapy*)

**Blind assessment**: The evaluation of an outcome is
made without the evaluator knowing which results are from the test under
study and which are from the control or gold standard.

(*Diagnosis*)

**Blind(ed)
study (masked study**): A study in which observer(s) and/or subjects are
kept ignorant of the group to which the subjects are assigned, as in an
experimental study, or of the population from which the subjects come, as in a
nonexperimental or observational study. Where both observer and subjects are
kept ignorant, the study is termed a **double-blind study**. If
the statistical analysis is also done in ignorance of the group to which
subjects belong, the study is sometimes described as **triple
blind**. The purpose of "blinding" is to eliminate sources of bias.
(*Diagnosis, Harm/Etiology, Therapy*)

**Case-control
study**: Retrospective comparison of exposures of persons with disease
(cases) with those of persons without the disease (controls)
(*Harm/Etiology*). See Retrospective
study.

**Case-series**: Report of a number of cases of disease.
*(Harm/Etiology*)

**Causality**: The relating of causes to the effects they
produce. Most of epidemiology concerns causality and several types of causes
can be distinguished. It must be emphasized, however, that epidemiological
evidence by itself is insufficient to establish causality, although it can
provide powerful circumstantial evidence. (*Harm/Etiology)*

**CER**: see
Control Event Rate

**CI**: see see
Confidence Interval

**Clinical
outcome**: Measures patient health or well being. Ideally it should be
credible, comprehensive, sensitive to change, accurate, sensible, and
biologically sensible. Compare with Surrogate
outcome. (*Diagnosis, Harm/Etiology, Prognosis, Therapy*)

**Clinical Practice
Guideline**: A systematically developed statement designed to assist
clinician and patient decisions about appropriate health care for specific
clinical circumstances.

**Co-interventions**:
Interventions other than the treatment under study that may have been applied
differently to the study and control groups. Co-intervention is a serious
problem when double-blinding is absent or when the use of
very effective non-study treatments is permitted. (*Therapy*)

**Cohort
study**: A study that begins with the gathering of two matched groups
(the cohorts), one which has been exposed to a prognostic factor,risk
factor or intervention and one which has not. The groups are then followed
forward in time (prospective) to measure the
development of different outcomes. In a retrospective
cohort study**,** cohorts are identified at a point of time in
the past and information is collected on their subsequent outcomes.

(*Diagnosis, Harm/Etiology, Prognosis, Therapy*)

An
**inception cohort** is a group identified at the onset of a
disorder or a first exposure to a potential risk
factor, and followed forward in time. (*Harm/Etiology,
Prognosis*)

**Comparison group**: Any group to which the index group
is compared. Usually synonymous with control group. (*Harm/Etiology,
Therapy*)

**Co-morbidity**: Coexistence of a disease or
diseases in a study participant in addition to the index condition that is the
subject of study. (*Harm/Etiology*,* Prognosis, Therapy*)

**Confidence interval
(CI**): "The CI gives a measure of the precision (or uncertainty) of
study results for making inferences about the population of all such patients".
(Strauss, 2005 p. 263) The 95% CI is the range of values within which we can be
95% sure that the true value lies for the whole population of patients from
whom the study patients were selected. Wide confidence intervals indicate less
precise estimates of effect. CI is affected by sample size and by variability
among subjects. The larger the trial's sample size is, the larger the number of
outcome events and the greater the confidence that the true relative risk
reduction is close to the value stated: the confidence intervals narrow and
"precision" is increased.

(*Harm/Etiology, Therapy*)

**Confounding
variable** **(confounder)**: A characteristic that may be
distributed differently between the study and control groups and that can
effect the outcome being assessed. Confounding may be due to chance or
bias. See Adjustment, Selection bias

(*Harm/Etiology,
Therapy*)

**Cost-benefit analysis**: Assesses whether the cost of
an intervention is worth the benefit by measuring both in the same units;
monetary units are usually used.

**Cost-effectiveness analysis**: Measures the net cost of
providing a service as well as the outcomes obtained. Outcomes are reported in
a single unit of measurement.

**Crossover study design**: The administration of 2 or
more experimental therapies one after the other in a specified or random order
to the same group of patients.

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

**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.

**Dose-response
relationship**: A relationship in which change in amount, intensity, or
duration of exposure is associated with a change--either an increase or
decrease--in frequency or intensity of a specified outcome.
(*Harm/Etiology*)

**Determinant**: Any definable factor that effects a
change in a health condition or other characteristic.
(*Harm/Etiology*)

**Ecological survey:** A survey based on aggregate data
for some population as it exists at some point or points in time; to
investigate the relationship of an exposure to a known or presumed risk factor
for a specified outcome.

**EER:** see Experimental Event
Rate

**Effectiveness:** A measure of the benefit resulting
from an intervention administered under usual conditions of clinical care for a
particular group of patients. See Intention to
treat**.** (*Therapy*)

**Efficacy**: A
measure of the benefit resulting from an intervention for a given health
problem administered to patients under ideal conditions (i.e., perfect
compliance). (*Therapy*)

**Etiology: **The study of the cause or origin of a
disease.

**Event rate: **The proportion of patients in a group in
whom the event is observed. Thus if out of 100 patients, the event is observed
in 27, the event rate is 0.27.

**Evidence based health care:** The conscientious,
explicit and judicious use of current best evidence in making decisions about
the care of individual patients. Involves all professions associated with
health care including purchasing and management.

**Evidence-based medicine (EBM):** The conscientious,
explicit and judicious use of current best evidence in making decisions about
the care of individual patients. The practice of EBM means integrating
individual clinical expertise with the best available external clinical
evidence from systematic research.

**Exclusion criteria:** Stated conditions which preclude
entrance of candidates into an investigation even if they meet the inclusion
criteria. (*Diagnosis, Harm/Etiology, Prognosis, Therapy*)

**Experimental event rate (EER)**: The
percentage of intervention/exposed group who experience outcome in
question.

**Follow-up**:
Observation over a period of time of an individual, group, or initially defined
population whose relevant characteristics have been assessed in order to
observe changes in health status or health-related variables.
(*Harm/Etiology, Prognosis*, *Therapy*)

G

**Gold standard
(also Reference standard):** Ideally, the criterion used to
unequivocally define the presence of a condition; or practically, the method,
procedure or measurement that is widely accepted as being the best available to
detect the presence of a condition. (*Diagnosis*)

H

**Heterogeneity**: This occurs when there is more
variation between the study results (in a systematic review) than would be
expected to occur by chance alone.

**Inception cohort**: A group
of patients who are assembled near the onset of the target disorder.

**Incidence**: The rate of
new cases of illness commencing during a specified time period in a given
population See also Prevalence.
(*Harm/Etiology*)

**Index test**: The test whose diagnostic accuracy is
being measured against the reference or gold
standard. (*Diagnosis*)

**Intention to treat
analysis**: Individual outcomes in a clinical trial are analyzed
according to the group to which they have been randomized, regardless of
whether they dropped out, fully complied with the intervention or crossed over
to the other treatment. By simulating practical experience intention to treat
analysis provides a better measure of effectiveness (as opposed to
efficacy). (*Therapy*)

**Interviewer
bias**: Systematic error due to interviewer's subconscious or conscious
gathering of selective data. (*Harm/Etiology*)

**Lead-time bias**: : Overestimation of survival because
of earlier diagnosisâ€”time of death does not change, just time
of diagnosis. (*Harm/Etiology, Prognosis*)

**Likelihood
ratio**: The likelihood ratio for a test result compares the likelihood
of that result in patients with disease to the likelihood of that result in
patients without disease.

**Likelihood ratio of a
negative test**: Ratio of the probability of a false negative result if
the disease is present to the probability of a true negative result if the
disease is absent.

**Meta-analysis**: Statistical synthesis of the results
from several studies that address the same question.

**N-of-1 trials**:
In such trials, the patient undergoes pairs of
treatment periods organized so that one period involves the use of the
experimental treatment and the other involves the use of an alternate or
placebo therapy. The patient and physicians are blinded, if possible, and
outcomes are monitored. Treatment periods are replicated until the clinician
and patient are convinced that the treatments are definitely different or
definitely not different.

**Negative predictive value**:
The proportion of people who receive a negative
test result who are truly free of the target disorder.

**NNT**: see Number Needed to
Treat

**Number needed to
treat (NNT): **The number of patients with a particular condition who
must receive an intervention to prevent the occurrence of one adverse outcome.

*(Therapy*)

**Number needed to harm (NNH)**: The number of
patients for whom there is one additional patient who experiences a harmful
outcome.

**Observational study (non-experiemental study)**:
Changes or differences in one characteristic (e.g. whether or not people
received a specific treatment or intervention) are studied in relation to
changes or differences in other(s) (e.g. whether or not they died), without the
intervention of the investigator. Examples are case
control and__ __cohort
studies.

**Odds**: A ratio between two
probabilitiesâ€”the probability of an event to a non-event.
(*Etiology/Harm, Therapy*)

**Odds ratio (OR): **The odds of
the experimental group showing positive (or negative) effects of an
intervention or exposure, in comparison to the control group.
(*Etiology/Harm, Therapy*)

**OR**: see Odds Ratio

P

**P value: **The possibility that any particular
outcome would have occurred by chance. Statistical significance is usually
p<0.05. Considered to be inferior to confidence intervals
in determining significance of studies.

**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).

**Power**:The ability of a study to demonstrate an
association or causal relationship between two variables, given that an
association exists. For example, 80% power in a clinical trial means that the
study has a 80% chance of showing a statistically significant treatment effect
if there really was an important difference between outcomes. If the
statistical power of a study is low, the study results will be questionable
(the study might have been too small to detect any differences).

By
convention, 80% is an acceptable level of power. (Bandolier; April 1, 2008.
http://www.jr2.ox.ac.uk/bandolier/booth/glossary/statpow.html
)

**Precision (statistical precision):** The range in which
the best estimates of a true value approximate the true value.

(*Diagnosis, Harm/Etiology, Prognosis, Therapy*)

See Confidence interval.

**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 target 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.

(*Diagnosis*)

**Prevalence**:
The proportion of persons with a particular disease within a given population
at a given time. (*Diagnosis)*

**Primary research:** Individual studies such as
randomized controlled trials, cohort studies, case-control studies,
cross-sectional studies, etc.

**Prognosis**: the
possible outcomes of a disease or condition and the likelihood that each one
will occur. (*Prognosis*)

**Prognostic factor**: A factor or indicator
(such as age or gender) related to an individualâ€™s
probability of developing a disease or other outcome. Compare with
risk factors. Neither prognostic nor__ __risk factorsnecessarily imply a cause and effect
relationship. *(Prognosis)*

**Prospective
study**: Study design where one or more groups (cohorts) of individuals
who have not yet experienced the outcome event in question are followed forward
in time and monitored for the number of such events which occur (*Diagnosis,
Harm/Etiology, Prognosis, Therapy*)

**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').

**Ra****ndomized controlled trial**: An
experimental comparison study in which participants are allocated via a
randomization mechanism to either an intervention/treatment group or a control
/placebo group, then followed over time and assessed for the outcomes of
interest. Participants have an equal chance of being allocated to either
group. (*Therapy*)

**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. (*Harm/Etiology*)

**Reference
standard**: See Gold standard.

**Referral
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. Physicians and
medical centers may attract individuals with specific disorders or exposures.
(*Prognosis*)

**Relative risk (RR)**: 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. (*Therapy, Harm/Etiology*)

**Relative risk reduction
(RRR)**: The extent to which a treatment reduces a risk, in comparison
with patients not receiving the treatment of interest.* (Therapy) *

**Reproducibility (repeatability, reliability):**
The results of a test or measure are identical or closely similar each time it
is conducted. *(Diagnosis)*

**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. (*Harm/Etiology*)

See also Case-control study.

**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 nor prognostic
factors necessarily imply a cause and effect relationship.
(*Harm/Etiology*)

**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

S

**Sample size**:
Is the size of the sample. Larger samples usually mean more precise results.
Sample size usually depends on the purpose of the study, the population size
from which the sample the sample will be pulled, as well as the level of
precision and the level of confidence or risk that is acceptable, and the
degree of variability in the attributes being measured.

**Selection
bias**: A bias in assignment or a
confounding variable that arises from study design
rather than by chance. These can occur when the study and control groups are
chosen so that they differ from each other by one or more factors that may
affect the outcome of the study. (*Harm/Etiology, Therapy*)

**Sensitivity (of a
diagnostic test):** The proportion of truly diseased persons, as
measured by the gold standard, who are identified
as diseased by the test under study. (*Diagnosis*)

**Sensitivity Analysis (economic studies)**:
A technique for testing the robustness of a decision analysis by repeating the
analysis with a range of probability and utility estimates.

**SnNout**: When a sign/test/symptom has a high
Sensitivity, a Negative result rules out the diagnosis. For example, the
sensitivity of a history of ankle swelling for diagnosing ascites is 93%;
therefore is a person does not have a history of ankle swelling, it is highly
unlikely that the person has ascites.

**Specificity (of a
diagnostic test)**: The proportion of truly non-diseased persons, as
measured by the gold standard, who are so identified by the
diagnostic test under study. (*Diagnosis*)

**SpPin**: What a sign/test/symptom has a high
Specificity, a Positive result rules in the diagnosis. For example, the
specificity of a fluid wave for diagnosing ascites is 92%; therefore if a
person does have a fluid wave, it rules in the diagnosis of ascites.

**Statistical
significance: **How likely the result is due to chance. The probability
that an event or difference occurred by chance alone.

**Stratification**: Division into groups. Stratification
may also refer to a process to control for differences in confounding variables, by making separate estimates for
groups of individuals who have the same values for the confounding variable.
(*Therapy*)

**Strength of inference**: The likelihood that an
observed difference between groups within a study represents a real difference
rather than mere chance or the influence of confounding
factors, based on both p values and confidence intervals.
Strength of inference is weakened by various forms of bias
and by small sample sizes. (*Harm/Etiology,
Therapy*)

**Surrogate outcome/endpoint:**
Intended to capture the treatment effect of an important clinical endpoint but
does not directly measure the clinical benefit of the intervention, substitutes
something we can measure for something we want to measure. Compare with
clinical outcome. (*Diagnosis, Harm/Etiology,
Prognosis, Therapy*)

**Survival
curve**: A graph of the number of events occurring over time or the
chance of being free of these events over time. The events must be discrete and
the time at which they occur must be precisely known. In most clinical
situations, the chance of an outcome changes with time. In most survival curves
the earlier follow-up periods usually include results
from more patients than the later periods and are therefore more precise.
(*Prognosis*)

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

**Test/treatment
thresholds:** The probability of disease above which we treat for the
disease and below which we do not treat. The treatment threshold is determined
by the costs and benefits of the treatment.

Values can be assigned to these thresholds from data on the reliability and potential risks of the diagnostic test and the benefits and risks of the diagnostic test and the benefits and risks of a specific treatment. Treatment should be withheld if the probability of disease is smaller than the testing threshold, and treatment should be given without further testing if the probability of the disease is greater than the test-treatment threshold. The test should be performed (with treatment depending on the test outcome) only if the probability of disease is between the two thresholds. The method exposes important principles of decision making and helps the clinician develop a rational, quantitative approach to the use of diagnostic tests.

The probability at which one should be indifferent between testing and treating.

**Validity:** The
degree to which the results of a study are likely to be true, believable and
free of **bias**. This is entirely independent of the precision of
the results and does not predict the results to your patients. (*Diagnosis,
Harm, Prognosis, Therapy*)

The
**internal validity** of a study refers to the integrity of the
experimental design.

The
**external validity** of a study refers to the appropriateness by
which its results can be applied to non-study patients or populations.

**Verification bias (work-up bias):** Occurs
when patients with negative test results are not evaluated with the gold
standard test. See also **Bias**.

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