Correlation 2

Question 1

What is statistical significance?

Answer 1

The sample shows that it is fairly unlikely that the data comes from a bigger sample with no correlation.

Question 2

Statistical significance shows

Answer 2

That a fair reflection of reality has been drawn

Question 3

What does a extremely low p value mean?

Answer 3

Just that it’s significant but you have to look at the r value to see the strength.

Question 4

What are the strength numbers of correlations?

Answer 4

.10 is small
.30 is moderate
.50 large

Question 5

What is coefficient of determination?

Answer 5

r-squared which can tell you how much variance x and y share in common.

Question 6

What is confidence intervals?

Answer 6

A way to see an estimate of the likely effect in the population

Question 7

What is bivariate normal distribution?

Answer 7

Each variable is normally distributed.

Each variable is normally distributed at all levels of the other variable.

Question 8

What is skewness?

Answer 8

It has to do with the lack of symmetry in a distribution.

Question 9

Draw a positive skewed distribution

Answer 9

Large at the beginning and low at the end

Question 10

Draw a negatively skewed distribution

Answer 10

Low at the beginning and large at the end.

Question 11

What is kurtosis?

Answer 11

This has to do with the peakedness of a distribution.

Question 12

What is leptokurtic?

Answer 12

A form of kurtosis. Very tall and slim

Question 13

What is mesokurtic?

Answer 13

A form of kurtosis. A normal curve distribution

Question 14

What is platykurtic?

Answer 14

A form of kurtosis. A low and wide distribution.

Question 15

What are the best ways to assess normality in correlation?

Answer 15

If you have around 200 participants it’s best to look at a histogram. You should only be concerned if the deviations from normality are severe.

Question 16

What if assumptions are not satisfied?

Answer 16

• change a level to .01 instead of .05.
• use stats that are not for interval data such as Spearman’s tho or Kendall’s T.
• Transform data

Question 17

What can a non-linear relationship do to the results?

Answer 17

Underestimate the correlation between x and y. Departures from linearity are serious, then Pearson’s r is not appropriate.

Question 18

Why are restricted range misleading?

Answer 18

Because they have a tendency to either reduce or inflate the correlation.

Question 19

What are outliers?

Answer 19

A data point standing off by itself and they can strongly influence the value of r and thereby leading to a wrong conclusion about the extent to which the two variables are related.

Question 20

How do we check for outliers?

Answer 20

Scatterplots

Question 21

When do we have a perfect positive correlation?

Answer 21

When x and y distributions have exactly the same shape

Question 22

When do we have a perfect negative correlation?

Answer 22

When x and y have exactly the same shape or when x and y distributions are oppositely skewed.