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Quiz 3 biostatistics > Statistical concepts I > Flashcards

Flashcards in Statistical concepts I Deck (17)
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1

when would you use a chi-squared statistic?

Compares observed cell frequences (ex: of a 2x2 table) with expected frequencies

2

Chi-squared formula

Sum of (O-E)^2/E

3

When is a chi-squared stat significant?

If it is >3.84

4

how do you determine how many degrees of freedom to use with a chi-squared statistic?

(r-1)x(c-1)

5

What is the formula for odds ratio?

p1/(1-P1) / p2/(1-p2)

6

When do you use a t test?

To compare the means between two groups

7

When do you use logistic regression?

When there are more than 2 binary variables

8

how do you calculate the t statistic?

Take the difference (P2-P1) and divide by the standard error of the difference

9

What sample size must you have for the standard t statistic calculation to work?

N>50

10

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

11

when do you use paired samples t test?

Comparison of pre and post study results (i.e. before vs after)

12

What is the required sample size for a paired t test?

100

13

when do you use one-way analysis of variance?

To compare more than 2 groups

14

what is the survival function?

probability that an individual will survive beyond time t

15

What is the survival curve?

Graph of the survival function

16

What is the hazard estimate?

Probability of dying in a given time interval

17

What stat test do you use for estimating survival curves?

log-rank test