Statistics Flashcards
Sensitivity calculation
True positives/number of people with disease
Specificity calculation
True negatives/number of people without the disease
Positive predictive value calculation
True positives/all positives
Negative predictive value calculation
True negatives/all negatives
Positive likelihood ratio calculation
Sensitivity/(1-specificity)
Negative likelihood ratio calculation
(1-sensitivity)/specificity
Variance calculation
(Value - mean) squared for each value and sum them
Divide by n-1
SD calculation
Square root of variance
What percentage of data is within 1 SD of mean?
68%
What percentage of data is within 2 SDs of mean?
95%
What percentage of data is within 3 SDs of mean?
99.7%
What is the coefficient of variation?
SD as a percentage of the mean
SD / mean x 100
SEM calculation
SD / square root of n
or
square root of SD squared / n
How do you normalise skewed data?
Take the log, square root, square, or reciprocal (1/x)
95% CI calculation
+/- SEM x 1.96
Calculation of SD in binomial sample
p = proportion e.g. 40%
p x (1-p)
Calculation of SEM in binomial sample
square root of: p x (1-p) / n
What is Poisson distribution?
Number of occurrences of an events per unit of time (distribution of discrete data)
Variance = mean
SD calculation for Poisson distribution?
Squre root of mean
(mean = variance)
Types of data
Nominal - naming scale e.g. eye colour
Ordinal - ordered values e.g. first, second, third
Discrete - integers
Continues - can be non-whole numbers
Interval - distance between values is the same and can be +ve or -ve e.g. 1, 2 ,3 or 5, 10, 15
Ratio - interval scale with fixed 0 e.g. height, weight
Statistical test for correlation between two variables
Normal - Pearson’s coefficient
Non-normal - Spearman’s ranked coefficient
Z score calculation?
(Value - mean) / SD
Maternal mortality ratio
Maternal deaths per 100,000 live births in a year
(8.2 in UK in 2008)
