Psy 201

Front 1

background for hypothesis testing

Back 1

1.expose participants to 2 or more levels of IV
2.determine size of f-ratio by comparing between and within group variance
3.set the cut-off for acceptable prob. that results are due to chance (alpha level)
4.calculate actual prob(p-value)

Front 2

P-value less than Alpha level

Back 2

prob that difference is due to chance is acceptable
Null hypothesis rejected
statistically significant difference b/w the groups

Front 3

P-value more than alpha level

Back 3

prob. that difference is due to chance is not acceptable
Null hypothesis is accepted
NOT statistically significatn

Front 4

Null hypothesis

Back 4

no difference between experimental and control groups in terms of DV

hypothesis of "no difference"

observed difference due to change, not IV

Front 5

testing Null hypothesis

Back 5

reject null when prob is small <.05

accept null when prob is large <.05

Front 6

alternative hypothesis

Back 6

2 groups are different in terms of DV
hypothesis of "differences exist"

observed difference due to IV (hopefully)

alt.rejected if null accepted
alt.accepted if null rejected

Front 7

type I error

Back 7

when reject Null, but shouldnt have

results say there is difference between groups..but difference is due to chance

prob of type I error=Alpha

Front 8

setting smaller alpha

Back 8

..and get significant results:
conservative
more confidence that difference not due to chance

Front 9

if set larger alpha value

Back 9

..and get significant results:
liberal
less confidence difference is not due to chance

Front 10

Power

Back 10

=ability of a statistical test to detect a relationship between variables (corr) or differences between groups (exp) when they exist

Front 11

power + alpha level

Back 11

smaller alpha reduces power, bigger alpha increases power
requires more between-group variance to show a difference
usually experimenter will not set higher than 0.5

Front 12

power + effect size

Back 12

(overlap between populations)
larger(less overlap)=increases power
manipulate IV using extreme differences b/w levels to show a difference
potential solution: pilot study

Front 13

power + within group variance

Back 13

less within group variance increases power
reduce it by reducing reliabilty of DV, consistent treatment of participants

Front 14

power + sample size

Back 14

increasing sample size increases power
larger the sample,the more confident we can be that the result was not due to chance

Front 15

determining power

Back 15

can determine # of participants required to get statistically significant findings
use large samples

Front 16

ANOVA

Back 16

can test any number of groups simultaneously to look for a difference
Tests the Null that no difference among all possible pairings of groups A thru D simultaneously

Front 17

T-test

Back 17

test for differences between 1 pair of groups t a time
(ex. AandB, AandC, AandD..)

Front 18

probability pyramiding

Back 18

with 4 levels (6 possible pairings), prob of Type I error increases from 0.5 to 0.26
(26% differences due to chance)

with 3 levels, probability of Type I error increases from 0.5 to 0.14

Front 19

Post-Hoc

Back 19

"after the fact" test
tells which pairs of groups are statistically different