stats Flashcards
(22 cards)
how to calculate specificity?
true negative/ (true negative + false positive)
true negative= people with negative test who are actually negative
false positive= people told they had the disease from test but dont actually
how to measure sensitivity?
True positive/ (true positive + false negative)
what is sensitivity?
proportion of patients with the condition who have a positive test result
what is specificity?
proportion of patients without the condition who have a negative test result
what is the positive predictive value?
the chance that the patient has the condition if the diagnostic test is positive
how to calculate positive predictive value?
TP/ TP + FP
what is the negative predictive value?
the chance that the patient does not have the condition if the diagnostic test is negative
how to calculate negative predictive value?
TN/ (TN + FN)
how to calculate the likelihood ratio for a positive test result?
sensitivity/ (1- specificity)
how to calculate ratio for a negative test result?
(1- sensitivity)/ specificity
what is incidence?
is the number of new cases per population in a given time period
For example, if condition X has caused 40 new cases over the past 12 months per 1,000 of the population the annual incidence is 0.04 or 4%.
what is prevalance
the total number of cases per population at a particular point in time
For example, imagine a questionnaire is sent to 2,500 adults asking them how much they weigh. If from this sample population of 500 of the adults were obese then the prevalence of obesity would be 0.2 or 20%.
what is the relationship between incidence + prevalence
prevalence = incidence * duration of condition
how to calculate number needed to treat?
1/(Absolute risk reduction) and is rounded to the next highest whole number
Absolute risk reduction:
Experimental (drug A) event rate = people cured / people received drug = 0.6
Control (placebo) event rate = people cured / people received drug = 0.5
what is usual measure outcome of a case control study
Odds ratio
what is usual measure outcome of a cohort study
relative risk.
Two (or more) are selected according to their exposure to a particular agent (e.g. medicine, toxin) and followed up to see how many develop a disease or other outcome.
what study
Cohort study
Patients with a particular condition (cases) are identified and matched with controls. Data is then collected on past exposure to a possible causal agent for the condition.
case control study
what types of study is good for rare diseases
case control study
what stats thing can be used to compare 2 sets of data
two sample T test
what stats thing can be used to compare 3 sets of data
ANOVA test
