Statistical concepts I Flashcards
when would you use a chi-squared statistic?
Compares observed cell frequences (ex: of a 2x2 table) with expected frequencies
Chi-squared formula
Sum of (O-E)^2/E
When is a chi-squared stat significant?
If it is >3.84
how do you determine how many degrees of freedom to use with a chi-squared statistic?
(r-1)x(c-1)
What is the formula for odds ratio?
p1/(1-P1) / p2/(1-p2)
When do you use a t test?
To compare the means between two groups
When do you use logistic regression?
When there are more than 2 binary variables
how do you calculate the t statistic?
Take the difference (P2-P1) and divide by the standard error of the difference
What sample size must you have for the standard t statistic calculation to work?
N>50
What do you do with a t statistic if you have n<50?
the data must follow a normal distribution to work. Also, some changes in the formula
when do you use paired samples t test?
Comparison of pre and post study results (i.e. before vs after)
What is the required sample size for a paired t test?
100
when do you use one-way analysis of variance?
To compare more than 2 groups
what is the survival function?
probability that an individual will survive beyond time t
What is the survival curve?
Graph of the survival function
