Stats Flashcards
What is standard error of mean (SEM)? what affects it?
How does SEM relate to confidence intervals?
BJA Jul 2019
Standard Error of mean = Standard Deviation / Square root sample size (n)
SEM - larger if a lot of variation in the population
smaller as sample size increases.
Errors as normally distibuted - used to estimate
95% CI = mean +/- (1.96 x SEM)
Meaning we are 95% confident the actual mean is within this range
What is a null hypothesis
Define p value
BJA Jul 2019
Null Hypothesis states there is no significant difference between specified populations, any observed difference being due to sampling or experimental error
Calculate the probability that an experiment would give us these data if the null hypothesis is true. Express this via a p-value 0=ímpossible, 1=certain
If the probability of the data is low, we reject the null hypothesis and conclude there must be a difference between groups.
P value = the probability of finding the observed result or a more extreme result, if the null hypothesis were true
Explain why hypothesis testing is used.
As it is easy, we can readily describe what we would expect of our data under a null hypothesis
We know how the data would behave, we can readily work out the probability of getting the result we did.
It makes a very simple starting point for our probability assessment.
