simplified formal definition Flashcards
Sensitivity
Proportion of true positives correctly identified as such by the test
False negative
True positives that are
incorrectly identified as negative
Specificity
Proportion of true negatives correctly identified as such by the test
(Specificity= 1- False positive)
False positive
True negatives that are
incorrectly identified as positive
Positive predictive value
Proportion of identified positives that are truly positive
Measure of process and
feasibility of running a screening programme
Confounder
A variable that is associated both with the exposure and the outcome and it is not on the causal pathway between exposure and outcome.
It gives an alternative
explanation for an association between exposure and outcome. It is nuisance and need to be controlled
Interaction
Effect modification
It is the situation where the association between exposure and outcome varies according to the level of a third factor
It is real effect that needs to be
detected and reported
Crude estimate
A measure of effect which has not been altered to take into account the effect of confounding factors
Adjusted estimate
A measure of effect which has been altered (by stratification or regression modelling) in order to take into account the effect of confounding factors
Regression analysis
Studies the association between two or more variables, where one is dependent on the other(s). This allows the dependent variable to be estimated given the value(s) of the other(s)
Direct (age) standardisation
– observed age-specific rates of death or disease from the study population are applied to standard population of known age structure, thereby calculating age-adjusted rate
Indirect (age) standardisation
– age-specific death rates of standard population are applied to the age structure of the study population and compare total number of observed deaths with the number expected
DSR
Directly standardised rate is total number of deaths (that would have been expected if the study population had the same age structure as the standard population) divided by total person-time of the standard population
SMR
Standardised mortality ratio is the ratio of observed to expected deaths obtained by indirect method of standardisation (usually expressed as a %)
p-value
It is the result of hypothesis testing. It is the probability of obtaining the observed or more extreme estimate if the null hypothesis (Ho) were true. Small p-value suggests that the null hypothesis is unlikely to be true.
Probability of making type I error i.e. wrongly rejecting Ho in favour of H1
95% Confidence interval
95% confident that the range of interval around the sample estimate contains the true population parameter
If the sampling is repeated thousands of times, the interval around the sample estimate will include the true population parameter 95% of the time
Power
Probability that an effect will be detected if it is truly there
Precision
Ability to measure magnitude of effect with minimal sampling error
Prevalence
Number of existing cases in a given time / total population at risk
Incidence risk
Number of new cases during a period of time / population at risk at the start of the period