Flashcards in Correlation Deck (24)

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1

##
What is the Pearson product-moment correlation coefficient?

What symbol is it represented by?

###
It looks at whether variables deviate from the mean in a similar way (co-vary)

BUT it is on a standardized scale to facilitate comparisons across units of measurement

denoted by "r"

2

## What type of data can the Pearson correlation coefficient (or its adaptations) be used for?

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Typically associated with looking at the relationship between variables measured on an interval or ratio scale

HOWEVER it can also be used for:

1. Ordinal variables when the raw scores have been converted to ranks

2. An interval or ratio scale variable with a dichotomous variable

3. Two dichotomous variables

Note that these have become adaptations with difference names

3

## List all types of variable combinations that adaptations of Pearson correlation coefficients can be used for

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1. Interval/Ratio + Interval/Ratio

2. Ordinal (ranked) + Ordinal (ranked)

3. Nominal (dichotomous) + Nominal (dichotomous)

4. Nominal (dichotomous) + Interval/Ratio

4

## What are the names of the simplified Pearson correlation coefficient formulas?

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1. Phi

2. Spearman

3. Point-biserial correlation

4. Pearson correlation

5

## What type of data is the Phi correlation coefficient used for?

### Nominal (dichotomous) + Nominal (dichotomous)

6

## What type of data is the Point-biserial correlation coefficient used for?

### Nominal (dichotomous) + Interval/Ratio

7

## What type of data is the Spearman correlation coefficient used for?

### Ordinal (ranked) + Ordinal (ranked)

8

## What type of data is the Pearson correlation coefficient used for?

### Interval/Ratio + Interval/Ratio

9

## What is the Spearman correlation coefficient denoted by?

### p or r subscript s

10

## When ranking data for a spearmen correlation coefficient - what do you do if two have the same value?

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You give both scores the same averaged rank

e.g. if those values would be rank 5 and 6 (but are the same so it wouldn't be possible order them) you would take the average of 5 and 6 (5.5) and assign both of the values the rank of 5.5

11

## How do you interpret a correlation coefficient?

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The correlation coefficient has to lie between -1 and +1

A coefficient of +1 indicates a perfect positive relationship, a coefficient of -1 indicates a perfect negative relationship, a coefficient of 0 indicates no linear relationship at all

12

## When used as a measure of effect size, what would small medium and large effect size of a correlation coefficient be?

### The correlation coefficient is a commonly used measure of the size of an effect: values of ±.1 represent a small effect, ±.3 is a medium effect and ±.5 is a large effect

13

## What type of correlation coefficient can be used for non-parametric data?

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Spearman

Kendall's tau

Both used for ranked ordinal data

14

## When should Kendall's tau be used instead of Spearman?

### When you have a small data set and many of the scores in your dataset have the same rank

15

## What does the Kendall's tau correlation coefficient compare?

### It looks at the number of concordant and discordant pairs

16

## What does the biserial correlation coefficient do?

### Estimates the degree of association between dichotomized continuous measure and a continuous measure

17

##
What is the difference between the biserial correlation coefficient and the point-biserial correlation coefficient?

Give 2 examples

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Biserial is used if the dichotomous variable has an underlying continuum between categories

e.g., of a dichotomous variable with underlying continuum passing or failing an exam -> some people might fail by a little bit vs a lot

e.g. of a dichotomous variable without an underlying continuum is being alive or dead (can't be a bit dead)

18

## How does the interpretation of the biserial correlation coefficient differ from that of the point-biserial correlation coefficient

### Interpretation of biserial is slightly different because it is an estimate of of the degree of association of the artificially dichotomized continuous variable if it had been evaluated as a true continuous variable

19

##
What is the rank biserial correlation coefficient used for?

what is a caution for interpretation

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To estimate the degree of association between a dichotomized continuous variable with an ordinal (ranked) variable

same caution as biserial -> estimate of the association had the artificially dichotomized variable been examined as continuous

20

## What is the phi-biserial correlation used for?

### used to examine the association between a true dichotomous variable and a continuous variable that has been dichotomized

21

## What is the tetrachoric correlation used for?

### to examine the association between 2 artificially dichotomized continuous variables

22

## What are 2 other types of correlation coefficients that are often seen in structural equation modeling?

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Polyserial correlation

Polychoric correlation

23

## What is the Polyserial correlation used for

### interval-scaled variable and continuous variable that has been dichotomized or categorized (ordinal)

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