[L6] Analyzing Data from Independent Groups: Continuous and Ordinal Measures Flashcards

1
Q
  • Most common experimental design in psychological
    research.
A

Independent Group Designs

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2
Q

Independent Group Designs- Used for comparing two (or more) groups which are
independent of one another – meaning there are ___
__
_ in each group.

A

different people

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3
Q

Independent Group Designs - Can be used for _____

A

true and quasi-experimental designs.

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4
Q

____ people are not assigned to
conditions, as they already belong to different groups.

A

Quasi-experimental designs –

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5
Q

Independent groups designs– __ different kinds of
__ can be used

A

three; dependent variable

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6
Q

Advantages of Independent Group Designs

A

Avoids the problems inherent in repeated measures
designs; practice effects, sensitization or carry-over
effects.

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7
Q

Disadvantage Independent Group Designs

A

more people, difficulty of matching
controlled group with experimental group

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8
Q

Statistical Tests for Independent Groups
Data

A
  1. The Independent Groups t-test
  2. The Mann-Whitney Test
  3. The Chi-Square Test
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9
Q

Use of test depends on data being tested.

A

Statistical Tests for Independent Groups
Data

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10
Q

The Mann-Whitney Test (also called the

A

Wilcoxon-
Mann Whitney Test)

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11
Q

also known as the between subjects t-test or the twosamples
t-test.

A

The Independent Groups t-test

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12
Q

Two (or Three) Assumptions about the Data

A
  1. Continuous/interval scale
  2. Data within each group is normally distributed. We
    need to make sure that the data are approximately
    normally distributed within each group.
  3. The SD of the two groups are equal
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13
Q

there are actually two kinds of t-test, one makes
the assumption of ___, and one
does not.

A

homogeneity of variance

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14
Q

Common Mistake:

A

Normal Distribution and the
Independent Sample t-test

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15
Q
  • To look at the overall distribution of data to determine
    whether the data are appropriate for an independent
    samples t-test.
  • It should be the ___ of the two groups.
A

distribution

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16
Q

Dispelling Myths
.

A
  1. Sample size must be above some value, such as 6, for
    the t-test to be valid.
  2. Sample sizes must be balanced, or similar
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17
Q

distribution of two (or more)
groups can be shown for the same amount of space.

A

Box and whisker plot –

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18
Q

We use the ____– approximately equal
sample sizes.

A

Pooled Variance t-test

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19
Q

Use ____ instead of histograms.

A

box and whisker plot

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20
Q

Check first the _____
(distribution of each group).

A

normal distribution assumption

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21
Q

The general form of the t-tests follow a
____

A

similar pattern.

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22
Q

Difference – in IG t-test, instead of being interested in
mean scores, we are now interested in the ____. So we call this ___

A

difference
between two means; d

23
Q

The Equal Standard Deviations Assumption
* Also known as _____

A

Homogeneity of Variance.

24
Q

Two versions of the t-test: the ____
which makes this assumption, and the _____ which does not make this assumption.

A

Pooled Variance t-test, Unpooled
Variance t-test,

25
If you have (approximately) equal sample sizes in your two groups, use the ____
pooled variance t-test.
26
If you don not have (approximately) equal sample sizes in the two groups, use the ____
unpooled variance t-test.
27
___ used to decide if variances (or SDs) are the same. (most common)
Levene’s test
28
If Levene’s test give gives a ____ result, this means variances are different from one another and the unpooled variance test should be used. (vice versa)
statistically significant
29
Problem however is that a ____does not mean that the variances are the same.
non-significant result
30
And the problems with the tests, such as the Levene test, is that they are dependent on the _____
sample size.
31
When the sample size is small, it is _____ in the variances. (vice versa)
not very good at detecting differences
32
It only matters however that the variances are the same when the sample size is ____.
small
33
So, when Levene’s test is good at telling us when the variances are different precisely ____
we do not really care.
34
And when it is _____ when we do care.
not very good is precisely
35
Homogeneity of variance does not really matter when the sample sizes are about ____
equal
36
So, if we have _____sample sizes, we can ignore the assumption of Homogeneity of Variance and use the Pooled Variances t-test.
equal (or approximately equal)
37
When the sample sizes are ___, Homogeneity of Variance matters a lot more.
unequal
38
* A modification of the t-test, which does not make the assumption of equal variances.
Unpooled Variance t-test
39
Sometimes known as ____which was developed by ____
Welch’s Test ; Welch (1938)
40
Reasons for having Unequal Sample Sizes
1. Comparison of two naturally occurring groups, and they are different sizes. 2. It may be difficult or expensive for one of the interventions. 3. There may be an ethical or recruitment issue.
41
We often describe the difference between two samples by stating the ___
difference between the two means.
42
However, often the scale that is used is not one that actually ____ (unless we are very familiar with the scale)
makes any sense
43
How do we tell then if the difference is good or bad?
Use a measure of Effect Size,
44
in the case of the independent groups t-test, an appropriate measure of effect size is called __ _
Cohen’s d.
45
---= measure of how far apart the means of the two samples are, in SD units.
Cohen’s d
46
It does not matter what the range of possible scores is – we are interpreting it in terms of _ _.
SD
47
Cohen’s d is often interpreted according to the following Rules:
* Large effect size: d = 0.8 * Medium effect size: d = 0.5 * Small effect size: d = 0.3
48
It can be as low as ____ and, unlike a correlation (which can not be higher than 1), it has no upper limit, although values above 1 are rare.
0 (It can not be negative)
49
* * Used when independent samples t-test can not be used. * Non-parametric test
The Mann-Whitney U Test
50
The Mann-Whitney U Test
Compares two unrelated groups.
51
The t-test compares the ___ of two groups and tells us whether the ___ is statistically significant.
means; difference in the means
52
The Mann-Whitney test does not compare means so it might be tempting to say that it compares _ __. Unfortunately it does not (necessarily)
medians
53
Effect Size for the Mann-Whitney test * Use the value called ___, which is the Greek Letter ___.
ϴ; theta