Statistics Flashcards
What is meant by a nominal variable?
A type of qualitative variable that does not have an inherent order. Examples include sex and blood type
What is meant by an ordinal variable?
A type of qualitative variable that has a natural or inherent ordering. Examples include much better/better/worse.
What is a categorical/qualitative variable?
A non numerical variable. The can be either nominal (no inherent order) or ordinal (an inherent order)
What is meant by a metric/quantitative variable?
A variable that is a real number. They can be either continuous (an unlimited amount of values such as weight) or discrete (limited number of values - usually from counting things_
What are the two factors that define normal distribution?
Normal distribution is a bell shaped curve. It is defined by the mean (where the curve is centred) and the standard deviation (how broad or thin the curve is)
In a normal distribution how many values will lie within +/-1 SD of the mean?
68.27%
In a normal distribution how many values will lie within +/-2 SD of the mean?
95.45%
In a normal distribution how many values will lie within +/-3 SD of the mean?
99.73%
What is meant by the p value?
The probability of obtaining a specific observed result by chance. The smaller the p value the more unlikely the result is to have occured by chance. Usually a p value of less than 0.05% is accepted.
What is meant by incidence?
The number of new cases of a disease occuring over a specified period of time
What is meant by prevalence?
The number of existing cases of a disease at a particular point in time
What is meant by sensitivity
A measure of how good a test is at detecting individuals who have the disease ie the true positive rate
What is meant by a test sensitivity of 90%?
It means that 10% of people with the disease will have a negative test (false negative). Tests with high sensitivity are good screening tests
What is meant by specificity?
A measure of how good a test is at detecting individuals who are not diseased ie the true negative rate.
What does a specificity of 80% mean?
20% of people without the disease ill get a positive result. A test with a high specificity are used to confirm a diagnosis.
What is the positive predictive value?
The probability that a patient with a positive test has the disease
PPV = Number of diseased people with a positive test/total number of tests
What is the negative predictive value?
The probability that a patient with a negative test is healthy
NPV - Number of healthy people with a negative test/number of negative tests
What is absolute risk reduction?
The benefit of one treatment over another. So if the risk in group 1 is R1 and the risk in group 2 in R2 then the ARR is R2 - R1
What is relative risk reduction?
The proportion of initial risk that was eliminated by the given treatment.
What is risk?
The probability of an occurance of an event within a given period of time
What is relative risk?
Comparison of risk in 2 different groups.
