Week 10

Question 1

When are t-tests used?

Answer 1

When you want to compare up to two sample means

Question 2

What does a one-sample t-test tell you?

Answer 2

Does a sample mean differ from some known mean?

Question 3

What does an independent samples t-test tell you?

Answer 3

Do means of two independent sample differ?

Question 4

What does a paired-sample t-test tell us?

Answer 4

Do means of two related samples differ?

Question 5

As a general assumption of t-tests, what kind of data is assumed?

Answer 5

interval or ratio data

Question 6

As a general assumption of t-tests, what is assumed about the distribution?

Answer 6

Population of scores is normally distributed. T-tests are reasonably robust to violations.

Question 7

As a general assumption of t-tests, what is assumed about the scores?

Answer 7

Scores for independent samples t-test are independent (e.g knowing one score provides no information about any other score).

Question 8

As a general assumption of t-tests, what is assumed about the variance?

Answer 8

That the variance is equal (for independent samples t test).

• homogeneity of variance (assume SDs are equal)
• Levene’s test

Question 9

Give some steps for using a one sample t-test with the example: do newborns show preference for more “attractive” faces?

Answer 9

1. newborns shown pictures of various female faces to measure average time looking at them
2. Locate critical region
3. Calculate the t-value
4. make a decision (compare obtained t to critical t)
   Therefore, infants stares significantly longer at attractive pictures

Question 10

When is an independent samples t-test used?

Answer 10

When we want to compare means from two groups

Question 11

What does the denominator look like in an independent samples t-test?

Answer 11

The denominator is standard error of difference between means

Question 12

In an independent samples t-test, what is known about the t-distribution?

Answer 12

The t-distribution varies with sample size.

Question 13

With the example of “how much anorexic individuals eat is a result of how much they feel in control”, demonstrate how an independent samples t-test would be used.

Answer 13

1. Twelve anorexic females were randomly assigned to a high control and low control group
2. Participants were expected to taste test. High control was hypothesis to eat a higher mean of cereal.
3. Two means of low and high control group were compared
4. Test of equality of variance. If p

Question 14

How can we summarise an independent samples t-test?

Answer 14

t value, p value, 95% CI and cohens d.

Question 15

Does Jamovi provide numerical 95% confidence intervals?

Answer 15

No.

Question 16

What will it mean if 95% CIs on means for independent t-test overlap no more than ~25% of their total length?

Answer 16

It will mean that the difference is statistically significant.

Question 17

What data is needed for a paired-samples t-test?

Answer 17

Interval or ratio

Question 18

What kind of distribution is needed for a paired-samples t-test?

Answer 18

population of scores is normally distributed (t-tests are reasonably robust to violations)

Question 19

With a paired samples t-test, what do the scores usually require?

Answer 19

For them to be independent (knowing one pair of scores provides no information about any other pair of scores)

Question 20

What is the expectation of scores in a paired-samples t-test?

Answer 20

Expect that pairs of scores will be correlated (not a requirement)

Question 21

What is a paired samples t-test actually testing?

Answer 21

Is the difference between means different from zero?

Question 22

What is an example of when a paired-sample t-test should be used?

Answer 22

Investigating whether reaction time for bimanual movements depends on which arm has to move accurately to precise location.

Question 23

What does it mean if in a paired-samples t-test (within-subject design), the 95% CIs overlap?

Answer 23

It means that visual inspection is not able to answer questions of statistical significance.

Question 24

If in the 95% CIs for two conditions overlap at any amount for a within subjects design, what must you do?

Answer 24

Consult the p-value in the t-test results for statistical significance.

Question 25

For a paired-samples t-test, what does Cohen’s d not take into account?

Answer 25

The correlation of the two conditions. This effect size is not directly comparable with d from independent samples t-test

Question 26

What is effect size in an t-test?

Answer 26

significance test is sensitive to sample size. Even small effect can be significance with a large enough n.

Question 27

What do we use to measure the effect size when testing significance (t-test)?

Answer 27

Cohen’s d. Measure of effect size which states the size of effect in SD units.

Question 28

What does a cohens d of 0.2 mean?

Answer 28

A small effect

Question 29

What does a cohens d of 0.5 mean?

Answer 29

A moderate effect

Question 30

What does a cohens d of 0.8 mean?

Answer 30

A large effect