T-test Flashcards by D E

Used when we have 1 IV with 2 levels

a. one-way ANOVA
b. t-test
c. two-way ANOVA

b. t-test

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What does the t-test estimate?

Estimates whether the population means under the 2 levels of the IV are different

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Estimates whether the population means under the 2 levels of the IV are different

a. one-way ANOVA
b. t-test
c. two-way ANOVA

b. t-test

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Independent t-test is for…?

a. Between subjects
b. Within subjects

a. Between subjects

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Paired t-test is for…?

a. Between subjects
b. Within subjects

b. Within subjects

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Used when we have 1 IV with 2 levels, between subjects

Independent t-test

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Used when we have 1 IV with 2 levels, within subjects

Paired t-test

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A researcher recruited 90 dogs and their owners to take part in an agility challenge.

Before the challenge began, she told half the owners (chosen at random) that their dog showed positive signs of agility potential, and the other half that their dog did not show potential.

She then timed how long it took each dog-owner pair to complete the agility course

What are the…?

a. IVs
b. IV levels
c. DV
d. Subjects design
e. Type of test

a. Expectation of potential
b. 2 (potential, no potential)
c. Agility performance (time to complete agility course)
d. Between subjects
e. Independent t-test

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What contributes to variance between IV levels in independent t-test?

List 3 things

Manipulation of IV (treatment effects)
Individual differences
Experimental error; random error and constant error)

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What contributes to variance within IV levels for independent t-tests?

List 2 things

Individual differences
Experimental error; random error)

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True or False?

Manipulation of IV (treatment effects) contributes to variance between IV levels

True

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True or False?

Manipulation of IV (treatment effects) contributes to variance within IV levels

False

Individual differences and experimental error (random error) contributes to variance between IV levels

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What type of experimental error(s) contribute to variance between IV levels?

Random error
Constant error

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What type of experimental error(s) contribute to variance within IV levelsfor indepdendent t-test?

Random error

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The t-distribution represents the distribution of sampled mean differences when…?

The null hypothesis is true

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The t-distribution has a mean of …?

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The extent to which an individual sampled mean difference deviates from 0 can be expressed in ______ units

Standard Error

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What is the formula for differences in ESE ?

Diff. ESE = sqrt (SD a^2 + SD b^2) / (Sample size A + Sample size B)

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True or False?

t is a ratio

True

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t reflects the difference between ________ , expressed
in _______ units

The sample means

standard error

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What can be used to determine the probability of measuring a t-value of the magnitude obtained (or greater), if the null hypothesis were true?

t-distribution

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What is the formula for t

t = variance between IV levels / variance within IV levels

t = x difference / ESE difference

t = xA - xB / sqrt ((SDa^2 + SDb^2) / Na + Nb))

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Is the variance between IV
levels relative to within IV levels large or small when t-value is close to 0?

Small

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Is the variance between IV
levels relative to within IV levels large or small when t-value is further from 0?

Large

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Small variance between IV levels relative to within IV levels t value is...? a. Close to 0 b. Far from 0

a. Close to 0

Large variance between IV levels relative to within IV levels t value is...? a. Close to 0 b. Far from 0

b. Far from 0

True or False? If the null hypothesis is true, 5% of sampled t-values will fall within the 95% bounds of the t-distribution

False If the null hypothesis is true, 95% of sampled t-values will fall within the 95% bounds of the t-distribution

True or False? If the null hypothesis is true, 95% of sampled t-values will fall outside the 95% bounds (in the tails of the distribution)

False If the null hypothesis is true, only 5% of sampled t-values will fall outside the 95% bounds (in the tails of the distribution)

If the magnitude of the obtained t-value is smaller than the critical value of t, we...? a. Fail to reject null b. Reject null

a. Fail to reject null

If the magnitude of the obtained t-value is greater than the critical value of t, we ...? a. Fail to reject null b. Reject null

b. Reject null

The difference between the number of measurements made and the number of parameters estimated sample size – no. parameters This is known as...?

Degrees of Freedom

What is df?

The difference between the number of measurements made and the number of parameters estimated sample size – no. parameters

The larger the degrees of freedom in an estimate, the _____ the estimate a. more reliable b. less reliable

a. more reliable

The ______ the degrees of freedom in an estimate, the less reliable the estimate a. Smaller b. Larger

a. Smaller

What is the df for independent t-test?

df = n - 2 of df = (nA-1) + (nB-1)

What are the 4 assumptions for independent t-test?

1. Normality 2. Homogeneity of variance 3. Equivalent sample size 4. Independence of observations

What is normality assumption for independent t-test?

The DV should be normally distributed, under each level of the IV

What is homogeneity of variance assumption for independent t-test?

The variance in the DV, under each level of the IV, should be (reasonably) equivalent

How do we check the homogeneity of variance on SPSS?

Levene's test if p < 0.5, we reject the null, the variance is not homogenous

What is equivalent sample size assumption for independent t-test?

Sample size under each level of the IV should be roughly equal

What is independence of observations assumption for independent t-test?

Scores under each level of the IV should be independent

What is the non parametric equivalent to the independent t-test?

Mann-Whitney U Test

Mann-Whitney U Test is the non parametric equivalent to a...?

Independent t-test

Do we ignore the +/- sign when reporting t-values?

Yes

What d.p. do you report t-values in?

2 d.p.

A student is convinced that he and his friends do better on their favourite arcade game when they are drunk than when they are sober. To test this theory he records the scores of 50 friends playing the game on two occasions; once when they are drunk, and once when they are sober (counterbalanced) a. IV(s) b. IV levels c. DV d. subject design e. type of test

a. Alcohol status b. 2 (sober, drunk) c. Arcade game score d. Within subjects e. Paired t-test

Used for within subjects/repeated measures designs a. Paired t-test b. Independent t-test

a. Paired t-test

What is the formula for t-ratio for paired t-test?

t = variance between IV levels / variance within IV levels or t = diff x (mean) / diff ese

What contributes to variance between IV levels in repeated measures design?

1. Manipulation of IV (treatment effects) 2. Experimental error

Why is there no variance due to individual differences in repeated measures design?

Because each participant acts as his/her own control

What contributes to variance within IV levels in repeated measures design?

1. Experimental error

What are the 2 assumptions for paired t-test?

1. Normality 2. Sample size

What is the normality assumption for paired t-test?

The distribution of difference scores between the IV levels should be approximately normal i.e. the calculated individual difference scores

What is the sample size assumption for paired t-test?

Sample size under each level of the IV should be roughly equal

What is the non parametric equivalent to a paired t-test?

Wilcoxon T Test

Wilcoxon T Test is the non parametric equivalent to...?

Paired t-test

When interpreting 95% CI plots for repeated measures, result is likely to be significant when...?

The difference between means (size of effect) is modest but the effect is consistent

The difference between means (size of effect) is modest but the effect is consistent The result is likely to be...? a. Significant b. Not significant

a. Significant

When interpreting 95% CI plots for repeated measures, result is not likely to be significant when...?

The difference between means (size of effect) is modest but the effect is not consistent

The difference between means (size of effect) is modest but the effect is not consistent The result is likely to be...? a. Significant b. Not significant

b. Not significant

True or False? For repeated measures designs, you can determine if result is likely to be significant by looking at (95% CI plot)

False For repeated measures designs, you cannot determine if result is likely to be significant by looking at (95% CI plot)

What is the formula to calculate t value on SPSS?

t = mean (of differences) / SE of mean (differences)

Do we report t-values less than 0 with a 0 in front of the decimal point? e.g. .539 -> t = 0.54

Yes

What is the df for paired t-test?

df = N - 1

The magnitude of difference between two IV level means, expressed in SD units i.e. a standardised value expressing the difference between the IV level means This is known as...?

Cohen's d

What is cohen's d?

The magnitude of difference between two IV level means, expressed in SD units i.e. a standardised value expressing the difference between the IV level means

What is the formula for cohen's d?

d = difference between sample means / mean sample SD or d = meanA - meanB / ((SD A + SD B) / 2)

Calculate the cohen's d for this: Potential Mean = 157.22 SD = 35.95 No potential Mean = 245.02 SD = 32.87

d = meanA - meanB / ((SD A + SD B) / 2) d = 157.22 - 245.02 / ((35.95 + 32.87) / 2) d = 2.55

Do you ignore the +/- sign when reporting cohen's d?

Yes

What d.p. do you report cohen's d in?

2 d.p.

What is considered a small cohen's d effect size?

0.2

What is considered a medium cohen's d effect size?

0.5

What is considered a large cohen's d effect size?

0.8

True or False? Cohen's d ignores sample size

True

The magnitude of difference between two IV level means, expressed in standard deviation units This is known as...? a. t b. Cohen's d

b. Cohen's d

The magnitude of difference between two IV level means, expressed in ESE units This is known as...? a. t b. Cohen's d

a. t

Ignores sample size a. t b. Cohen's d

b. Cohen's d

Qualifies the size of the effect in the context of the sample size a. t b. Cohen's d

a. t

On SPSS, cohen's d is calculated differently from the formula used to calculate by hand Which outcome will be very similar to hand calculation? a. Between subjects (independent t-test) b. Within subjects (paired t-test)

a. Between subjects (independent t-test)

On SPSS, cohen's d is calculated differently from the formula used to calculate by hand Which outcome may be quite different to hand calculation? a. Between subjects (independent t-test) b. Within subjects (paired t-test)

b. Within subjects (paired t-test)