Flashcards in Bivariable Associations Deck (60)

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1

## if p ≤ .05 then we...

### REJECT NULL

2

## if REJECT p > .05 then we...

### FAIL TO REJECT NULL

3

## What are the different bivariable statistical methods?

###
– T-test (independent samples t-test) and

ANOVA

– Chi-square test of independence

– Correlation

4

## What test do you use if you have a categorical variable and a continuous variable? (less than 3 categories)

### T-test

5

## What test do you use if you have a categorical variable and a continuous variable? (more than 3 categories)

### ANOVA

6

## What test do you use if you have two categorical variables?

### Chi-square test of independence

7

## What test do you use if you have two continuous variables?

### Correlation

8

## What is a critical value

###
the value associated with a particular

significance level

9

## Remember

###
Z tests use the z distribution

– T tests use the t distribution

– ANOVA uses the F distribution

– Chi-square test of independence uses the Χ2 distribution.

10

## List each statistic for the test of association

###
– t statistic (t-test)

– F statistic (ANOVA)

– Χ2 statistic (chi-square test of independence)

11

## What is a t test

### A statistical procedure that allows us to test whether the data from the two groups are the same or different.

12

## What is the null hypothesis for t tests. Put equation and words

###
--H0: μ1 = μ2

μ1 – μ2 = 0

--Mean of the data from sample 1 = mean of the data from sample 2

--Rejecting the null hypothesis implies that the means of the sample are

statistically significantly different

• Failure to reject the null hypothesis implies that the two means of the

sample are statistically insignificantly different (the same).

• And thus we assume this is true for the populations.

13

## what is the t test formula

###
For numerator: [(x1 – x2) – (x bar1 – x bar2)]

For denominator: √[s2 pooled[(1 / n1) + (1 / n2)] ]

14

## Two assumptions of the t test

###
•Both parent populations are normally distributed

• Both populations have equal variance

(homogeneity of variance)

15

## How do you calculate homogeneity of variance

###
– Levene’s test for equality of variances:

• Null hypothesis: variance1 = variance2

• p ≤ 0.05 implies that the variances are different

• p > 0.05 implies that the variances are the same

(– Violations of homogeneity of variance may be ignored as long as the samples being used have equal or

approximately equal sizes)

16

## How do you calculate degrees of freedom for t test (t-test degrees of freedom POOLED)

### Degrees of freedom (df) = (n1+n2-2)

17

## How do you calculate t-test degrees of freedom (unequal df’s)

###
df conservative = the smaller of df1 and df2

df1 = (n1 – 1) and df2 = (n2 – 1)

18

## When should you use ANOVA

### Used with 3 or more groups to test for MEAN DIFFS

19

## What is the null hypothesis for ANOVA

### H0: μ1=μ2=μ3

20

## What is the alternative hypothesis for ANOVA

### H1: μ1"≠μ2"≠μ3

21

## What is the null hypothesis for ANOVA in words

### All populations have the same mean

22

## What is the alt hypothesis for ANOVA in words

### Not all populations have the same mean

23

## What is the statistic for ANOVA

### f stat

24

## If F > Fcrit then we...

### reject the null hypothesis, meaning that there is some significant difference across all means

25

## IF F < Fcrit then we...

### fail to reject the null hypothesis bc the means are equivalent

26

##
What is the summary of procedures for testing

bivariable associations

###
Step 1: determine what kind of variables you have

• Step 2: determine which statistical procedure to use based

on the two variables

• Step 3: compute the appropriate test statistic

• Step 4: determine if the test statistic exceeds the critical

value (the value that corresponds to p ≤ 0.05)

– If it exceeds the critical value: REJECT the null hypothesis

– If it does not exceed the critical value: FAIL TO REJECT the null

hypothesis

27

## Purpose of ANOVA (f crit)

###
ANOVA determines F statistic which we test for

significance (Is F > Fcrit at p =.05 level?)

28

## Note about leven's test for equality of varianes

### We use Levene’s test for equality of variances—If the p-value associated with Levene’s test is less than alpha, the homogeneity of variance assumption is violated. If p > α, the homogeneity of variance assumption is met.

29

## What is the ANOVA f statistic

###
A ratio of the Between Group Variation divided by

the Within Group Variation: F=between/within=MSB/MSW

*A large F is evidence against H0, since it indicates that there is more difference between groups than within groups.

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