Independent one-way ANOVA Flashcards
Used when we have 1 IV with more than 2 levels
One-way ANOVA
Used when we have 1 IV with more than 2 levels, between subjects
One-way independent ANOVA
Used when we have 1 IV with more than 2 levels, within subjects
One-way repeated measures ANOVA
What does one-way ANOVA estimate?
Estimates whether the population means under the different levels of the IV are different
Estimates whether the population means under the different levels of the IV are different
This is known as…?
One-way ANOVA
One-way ANOVA estimates whether the population means under the different levels of the IV are different
What are the estimates based on?
The difference between the
measured sample means
Why use ANOVA and not stick to t-tests for studies with more than 2 IVs?
List 3 points
- With each IV levels, we’d have to run different t-tests
e.g. With 3 IV levels, we’d have to run 3 t-tests
- For each of these t-tests there would be a 5% chance of making a Type 1 error
- But the overall Type 1 error rate (across all t-tests) would be higher
Explain the sock drawer analogy in 3 points
- Sock drawer contents:
- 19 pairs of black socks
- 1 pair white socks - If you randomly pick out one pair:
- 1 in 20 chance of picking out the white socks (5%) - If you repeatedly go back and randomly pick out socks (returning those previously picked to the drawer)
- Chance of eventually picking out the white socks increases (>5%)
The probability that at least one of a ‘family’ of comparisons, run on the same data, will result in a
Type I error
This is known as…?
Familywise Error Rate
Describe Familywise Error Rate
The probability that at least one of a ‘family’ of comparisons, run on the same data, will result in a Type I error
The probability that at least one of a ‘family’ of comparisons, run on the same data, will result in a…?
a. Type I error
b. Type II error
a. Type I error
What is the formula for familywise error rate?
a’ = 1 - (1 - a)^c
or
Error rate for family of comparisons = 1 - (1 - Level of confidence we’re working to for each comparison (.95 if α=.05)^Number of comparisons
This study had 3 IV levels (A, B & C)
a. What is the familywise error rate?
b. What is the chance of Type I error?
A - B
A - C
B - C
= 3 comparisons
a.
a = 1 - (1 - 0.05)^3
a = .143
b. 14%
This study had 5 IV levels (A, B, C, D & E)
a. What is the familywise error rate?
b. What is the chance of Type I error?
A - B
A - C
A - D
A - E
B - C
B - D
B - E
C - D
C - E
D -E
= 10 comparisons
a.
a = 1 - (1 - 0.05)^10
a = .401
b. 40%
How many d.p. do we report Familywise error rate in?
3 d.p.
Do we include a 0 in front of the decimal point when reporting familywise error rate?
No
What tests control for the familywise error rate?
Omnibus tests (e.g. ANOVA)
Omnibus tests (e.g. ANOVA) control for…?
Familywise error rate
What is the formula for the F ratio in one-way ANOVA?
F = variance between IV levels / variance within IV levels
Is the variance between IV
levels relative to within IV levels small or large when the F value is close to 0?
Small
Is the variance between IV
levels relative to within IV levels small or large when the F value is further from 0?
Large
The variance between IV
levels relative to within IV levels is small when the F value is…?
a. Far from 0
b. Close to 0
b. Close to 0
The variance between IV
levels relative to within IV levels is large when the F value is…?
a. Far from 0
b. Close to 0
a. Far from 0
What contributes to variance between IV levels in independent designs?
List 3 things
- Manipulation of IV (treatment effects)
- Individual differences
- Experimental error (Random error, Constant error)
What contributes to variance within IV levels in independent designs?
List 2 things
- Individual differences
- Experimental error (Random error)
Variance between IV levels includes…?
- The variance caused by the manipulation of the IV
- Error variance
Variance within IV levels includes…?
- Only error variance
Total variance is the sum of…?
Variance between IV levels
(incl. variance explained by our model and error variance, aka ‘model’ variance) and Variance within IV levels (only error variance, aka ‘residual’ variance)
Residual variance is known as…?
Variance within IV levels
Model variance is known as…?
Variance between IV levels
Variance between IV levels is also known as…?
Model variance
Variance within IV levels is also known as…?
Residual variance
How do we partition the variance?
List 4 points
- Calculates the means for each IV level
- Calculates the grand mean
- Sum of IV level means, divided by the number of IV levels
- Calculates the within IV levels variance
- Sum of squared differences between individual values and the corresponding IV level mean
- Calculates the between IV levels variance
- Sum of squared differences between each IV level
mean and the grand mean
An investigator wants to determine whether participants recall more items in a verbal short term memory task if they have been instructed to use a mnemonic strategy.
He recruits 60 participants and randomly assigns them to one of 3 groups: no mnemonic, mnemonic 1 or mnemonic 2. He records how many items they can recall for a list of 20 words
What are the:
a. IVs
b. IV levels
c. DV
d. Subjects design
e. Type of test
a. Mnemonic strategy
b. 3 (No mnemonic, mnemonic 1, mnemonic 2)
c. Items/words recalled
d. Between subjects
e. One-way independent ANOVA
What are the 4 assumptions for independent one-way ANOVA?
- Normality
- Homogeneity of variance
- Equivalent sample size
- Independence of observations
What is the normality assumption for independent one-way ANOVA?
The DV should be normally distributed, under each level of the IV
What is the homogeneity of variance assumption for independent one-way ANOVA?
The variance in the DV, under
each level of the IV, should be (reasonably) equivalent
How do we check homogeneity of variance on SPSS?
Levene’s test
If p < 0.05, we reject the null, data is not homogenous
What can correct for homogeneity of variance for independent one-way ANOVA?
Welch F statistic
Welch F statistic can correct for…?
Homogeneity of variance
Levene’s test checks for…?
Homogeneity of variance
What is the equivalent sample size assumption for independent one-way ANOVA?
Sample size under each level of the IV should be roughly equal
What is the independence of observations assumption for independent one-way ANOVA?
Scores under each level
of the IV should be independent
What is the non parametric equivalent for the independent one-way ANOVA?
Kruskal WallisTest
Kruskal WallisTest is a non parametric equivalent for…?
Independent one-way ANOVA
What is the H0 for Levene’s hypothesis?
There is no difference between the variance under each level of the IV (i.e. homogeneity)
If p < .05 on the Levene’s test, we reject null hypothesis which means…?
The data is heterogenous
Where do we find Levene’s statistic on SPSS?
The ‘Based on Mean’ row on the ‘Test of Homogeneity of Variances’ table
How do you present the SPSS output of independent one-way ANOVA?
F(dfm,dfr) = F-value, p = p-value
or
F(Between Groups Sum of Squares, Within Groups Sum of Squares) = F, Sig.
Where the assumption of homogeneity of variance has been violated (i.e. a significant Levene’s result), we should report the result of …?
Welch’s F test
How do we report the results on SPSS of Welch’s F test?
F(df1,df2) = Statistic, Sig.
Sum of squared differences between IV level means and grand mean (i.e. between IV level variance)
This is known as…?
Model Sum of Squares (SSM)
What is Model Sum of Squares (SSM)?
Sum of squared differences between IV level means and grand mean (i.e. between IV level variance)
Sum of squared differences between individual values and corresponding IV level mean (i.e. within IV level
variance)
This is known as…?
Residual Sum of Squares (SSR)
What is Residual Sum of Squares (SSR)?
Sum of squared differences between individual values and corresponding IV level mean (i.e. within IV level
variance)
What is the formula for Mean Square Between Groups (MSM)?
Sum of Squares Between Groups (SSM) / df Between Groups (dfM)
What is the formula for Mean Square Within Groups (MSR)?
Sum of Squares Within Groups (SSR) / df Within Groups (dfR)
What is the F value formula on SPSS?
F = Mean Square Between Groups (MSM) / Mean Square Within Groups (MSR)
How many df values does independent one-way ANOVA have?
2
- df model (between IV levels)
- df residual (within IV levels
How do you calculate the df model (between IV levels) for independent one-way ANOVA?
df model = k (number of IV levels) - 1
How do you calculate the df residual (within IV levels) for independent one-way ANOVA?
df residual = N (sample size) - k (number of IV levels)
Between IV level variance is known as…?
Model variance
Within IV level variance is known as…?
Error/Residual variance
N (sample size) - k (number of IV levels)
This is the formula to calculate the df for…?
Within IV levels or df residual
This is the formula to calculate the df for…?
k (number of IV levels) - 1
Between IV levels or df model
What are Post-hoc tests?
Secondary analyses used to assess which IV level mean
pairs differ
Secondary analyses used to assess which IV level mean
pairs differ
This is known as…?
Post-hoc tests
When are Post-hoc tests used?
When F-value is significant
Post-hoc tests are run as t-test but include…?
Correction for multiple
comparisons
What are the 3 types of Post-hoc tests?
- Bonferroni
- Least Significant Difference (LSD)
- Tukey Honestly Significant Difference (HSD)
What is the Type I Error risk for Bonferroni?
a. Very high
b. High
c. Low
d. Very low
d. Very low
What is the Type I Error risk for Least Significant Difference (LSD)?
a. Very high
b. High
c. Low
d. Very low
b. High
What is the Type I Error risk for Tukey Honestly Significant Difference (HSD)?
a. Very high
b. High
c. Low
d. Very low
c. Low
What is the Type II Error risk for Bonferroni?
a. Very high
b. High
c. Low
d. Very low
a. Very high
What is the Type II Error risk for Least Significant Difference (LSD)?
a. Very high
b. High
c. Low
d. Very low
c. Low
What is the Type II Error risk for Tukey Honestly
Significant Difference (HSD)?
a. Very high
b. High
c. Low
d. Very low
b. High
What is the classification for Bonferroni?
“very conservative”
What is the classification for Least Significant Difference (LSD)?
“liberal”
What is the classification for Tukey Honestly Significant Difference (HSD)?
“reasonably
conservative”
This post-hoc test is classified as “reasonably
conservative”
a. Bonferroni
b. Least Significant Difference (LSD)
c. Tukey Honestly Significant Difference (HSD)
c. Tukey Honestly Significant Difference (HSD)
This post-hoc test is classified as “liberal”
a. Bonferroni
b. Least Significant Difference (LSD)
c. Tukey Honestly Significant Difference (HSD)
b. Least Significant Difference (LSD)
This post-hoc test is classified as “very conservative”
a. Bonferroni
b. Least Significant Difference (LSD)
c. Tukey Honestly Significant Difference (HSD)
a. Bonferroni
This post-hoc test has a very low Type I Error risk
a. Bonferroni
b. Least Significant Difference (LSD)
c. Tukey Honestly Significant Difference (HSD)
a. Bonferroni
This post-hoc test has a high Type I Error risk
a. Bonferroni
b. Least Significant Difference (LSD)
c. Tukey Honestly Significant Difference (HSD)
b. Least Significant Difference (LSD)
This post-hoc test has a low Type I Error risk
a. Bonferroni
b. Least Significant Difference (LSD)
c. Tukey Honestly Significant Difference (HSD)
c. Tukey Honestly Significant Difference (HSD)
This post-hoc test has a low Type II Error risk
a. Bonferroni
b. Least Significant Difference (LSD)
c. Tukey Honestly Significant Difference (HSD)
b. Least Significant Difference (LSD)
This post-hoc test has a high Type II Error risk
a. Bonferroni
b. Least Significant Difference (LSD)
c. Tukey Honestly Significant Difference (HSD)
c. Tukey Honestly Significant Difference (HSD)
This post-hoc test has a very high Type II Error risk
a. Bonferroni
b. Least Significant Difference (LSD)
c. Tukey Honestly Significant Difference (HSD)
a. Bonferroni
What are the 2 different effect sizes calculated for ANOVA?
- Partial n2
- Cohen’s d
How much variance in the DV is explained by the manipulation of the IV overall
What effect size is this?
Partial n2
The magnitude of the difference between pairs of IV level means, expressed in SD units
What effect size is this?
Cohen’s d
What does partial n2 tell us?
How much variance in the DV is explained by the manipulation of the IV overall
What does Cohen’s d tell us?
The magnitude of the difference between pairs of IV level means, expressed in SD units
What is considered a small effect size of partial n2?
> .01
What is considered a medium effect size of partial n2?
> .06
What is considered a large effect size of partial n2?
> .14
What proportion of the variance in the DV is accounted for by the manipulation of the IV?
This is known as…?
Partial eta^2
What does partial eta^2 tell us?
What proportion of the variance in the DV is accounted for by the manipulation of the IV?
What is the formula for partial eta^2?
Partial eta^2 = SSM / (SSM + SSR)
or
Partial eta^2 = Sum of Squares Between Groups / (Sum of Squares Between Groups + Sum of Squares Within Groups)
How many d.p. do you report partial n^2 or partial eta^2?
3 d.p.
Do you put a 0 in front of the decimal point when reporting partial n^2 or partial eta^2?
No
Calculate the Cohen’s d for each pair of the IV level means
Data:
No Mnemonic
Mean = 8.40
SD = 1.82
Mnemonic 1
Mean = 9.85
SD = 1.53
Mnemonic 2
Mean = 10.40
SD = 1.76
NM & M1
d = 8.40 - 9.85 / (1.82 + 1.53 / 2)
d = (-) 0.87 (large effect size)
NM & M2
d = 8.40 - 10.40 / (1.82 + 1.76 / 2)
d = (-) 1.12 (large effect size)
M1 & M2
d = 9.85 - 10.40 / (1.53 + 1.76 / 2)
d = (-) 0.33 (small effect size)