t-tests between + within

Question 1

If obtained t score is larger than t-table, probability of getting that large by chance is…

Answer 1

less than .05 P<.05
reject the null hypothesis

the independent variable is influencing something

Question 2

Between-subjects t-test
ASSUMPTIONS

Answer 2

1. dependent on interval or ratio scale
2. both samples norm distr
3. populations equal variance - homogeneity, levenes test
4. Independence of observations

Question 3

Between subjects t-test STEPS

Answer 3

1. estimate popn SD (each group)
2. pooled s2pool (n -1)
3. Standard error of mean diffs. (n is whole number)
4. mean differences
5. t-score using what you calculated
6. t-table, obtained larger than table reject null
7. cohens d uses s2 pool

Question 4

one-tailed

Answer 4

one
- double the alpha level .1 on table
- know before ‘a priori’ whether correlation is positive or negative
- null r = 0
- positive r > 0
- negative r < 0

Question 5

two-tailed

Answer 5

two
- 0.05 on table
- cant predict/doesnt specify whether correlation + or -
- null = no correlation btwn variables
- alternative = is correlation

Question 6

Outcomes - null or alternative hypothesis

Answer 6

H0 null = the groups show no performance difference
H1 = the groups show performance difference

Question 7

bessels correction N-1

Answer 7

only for estimating, ie population standard deviation

Question 8

T-Distribution is

Answer 8

the distribution obtained from an estimated population SD

Question 9

t-score is

samples over or under estimate standard error?

Answer 9

how many standard error units our sample mean is away from the mean

Samples OVERestimate standard error
t is platy, increase sample =z-norm

Question 10

effect size

Cohens D values

Answer 10

estimates proportion of variability in scores on dependent variable explainable by variation in the level of the indepdendent variable
- is result meaningful?

small .2, med .5 large .8

Question 11

repeated measures (Within) is

Answer 11

experience both levels of condition (IV)

Question 12

Repeated measures assumptions

Answer 12

• dependent variable on interval/ratio
• sample diff scores norm distrib.
• scores are related across conditions
  –> same individual
  –> less variability of individual differences

Question 13

repeated-measures steps

Answer 13

1. estimate variance of popn
2. estimate standard error
3. obtained t-value
4. t-table (if obtained is larger, reject null)