Applied Statistics 2 Flashcards
What is a contingency table?
table that displays the frequency distribution of two categorical variables
What is the Experimental Event Rate?
Proportion of animals receiving the test treatment that have the event of interest
What is the Control Event Rate?
Proportion of animals in the control group that have the event of interest
What is risk reduction?
Refers to the reduction of a bad event/ outcome occuring due to an intervention or treatment
What is absolute risk reduction?
The absolute difference between the control and the experimental group
What is relative risk reduction?
is the proportion by which the treated group improves
compared to the control group; it tells you by how much the treatment reduced the risk of a bad outcome relative to the control group
What is NNT?
Number needed to treat
The number of subjects/ animals that need to be treated in order to have one succesful outcome
How is NNT calculated?
calculated as the inverse of the absolute risk reduction
What does a negative NNT imply?
Implies that the treatment is harmful
What is the NNH?
number of subjects/ animals that need to be treated in order to have an additional bad outcome
What does the width of the confidence interval indicate?
Indicates the precison of the estimate
What are diagnostic tests used for?
tests performed to determine the presence or absence of a specific disease, condition, or infection in an individual
What does a diagnostic test evaluation study evaluate?
evaluate test’s
accuracy, comparing its results to a reference gold
standard to determine its reliability and clinical utility
How do you estimate statistical measures for diagnostic tests?
each animal needs to be classified definitively using a ‘gold-standard’ assessment
What is the definition of sensitivity?
The proportion of truly positive cases that are correctly identified as such
What is the definition of specificity?
The proportion of truly negative cases that are correctly identified as such
What is a Positive Predictive value
Proportion of test positives that are truly positive
What is a negative predictive value?
Proportion of test negatives that are truly negative
What does lowering the test threshold increase?
increases the sensitivity of the test and lowers specificity
What does increasing the test threshold increase?
Increases the specificity and lowers the sensitivity
What is a likelihood ratio?
statistical tool for assessing how good a diagnostic test is, derived from sensitivity and specificity
What is a positive likelihood ratio?
measures how much likely a positive test result is in individuals with a disease compared to those without
What is a negative likelihood ratio?
Measures how much more likely a negative test result is in individuals with a disease compared to those without
What is the definition of probability?
measures the likelihood of an event occuring, ranges from 0 to 1
What is the definition of odds?
Expresses the ratio of probability of success to the proabbaility of failure
What is pre-test probability?
The probability that an animal has a disease, before a test is carried out
What are pre-test odds?
Odds that an animal has a disease, before the test is carried out
What is absolute risk?
refers to the probability of an outcome occuring in a specific group regardless of any other factors
What is relative risk?
compares the risk of an outcome between different groups
What is the calculation of risk difference?
risk in exposed group - risk in unexposed group
