Week 7 (Correlation & Regression)

Question 1

Which of the 3 goals of science does correlational research have?

Answer 1

Describe and predict. Doesn’t and can’t involve explanation

Question 2

Why is internal validity low in correlational research?

Answer 2

Because of the way data is collected, there is a lack of control

Question 3

Why is external validity high in correlational research?

Answer 3

No strong control like other studies. Control removes external validity

Question 4

When is correlational research used?

Answer 4

When the manipulation of the independent variable is not possible, feasible or ethical.

For establishing reliability and validity
(Test-retest, convergent, discriminant)

Exploratory research

Question 5

Is research setting important in correlational research?

Answer 5

No. Even research done in a lab is correlational when no variables are manipulated or controlled

Question 6

What variables are involved in correlational research?

Answer 6

Both continuous or categorical variables can be involved

Question 7

What is the correlation coefficient?

Answer 7

Pearson’s r
Ranges from -1.00 to +1.00
Indicates the strength of relationship and sign indicates the direction

Question 8

What is a scatterplot?

Answer 8

A visual presentation of the relationship between two variables

Two measurements for each individual is represented by a single point

Question 9

How do we interpret a strong correlation?

Answer 9

It doesn’t mean there is a causal relationship
There is a possible third variable
Might be reversed- might not be in the direction that you think
Might reflect the influence of outliers

Question 10

How do we interpret a weak correlation?

Answer 10

Does not mean there isn’t a causal relationship
Might reflect curvilinear relationship (exponential growth)
Might reflect outliers
Might reflect truncated range (haven’t measured the variables over a big enough range to capture)

Question 11

What is a spurious correlation?

Answer 11

Relationship between two variables seems causal but is not, often is a potential third variable involved

Question 12

What is truncated range?

Answer 12

Occurs when haven’t captured enough data and only looking at a part of the range
Masks relationships or having what appears to be a relationship when there isn’t one at all

Question 13

What are the assumptions for Pearson’s r?

Answer 13

Linearity - straight line, not curved

Interval or ratio data - two continuous variables

Univariate normality - both variables should be normally distributed and have no outliers

Bi-variate normal - distribution of variables in combination should be normal

Question 14

Correlation coefficient sand their strengths?

Answer 14

0-.10 trivial
.10-.29 weak
.30-.49 moderate
.50-1.00 strong

Question 15

How to calculate a confidence interval for Pearson’s r

Answer 15

r needs to be converted to a z score

r and N can be used to calculate CI in the excel worksheet

Question 16

How do you summarise correlation?

Answer 16

r(N=x) = (correlation coefficient), p = x, 95% CI [x,y]

Plain English about strength of relationship
Statistics
Interpret confidence intervals
What these findings mean

Question 17

What is regression?

Answer 17

Quantifies the strength of association among one or more predictable variables and one criterion or outcome variable

Question 18

What is the intercept in simple regression?

Answer 18

It is the value of the outcome variable when the predictor variable is 0

By centring the predictor, it makes the intercept equal to the mean of the outcome variable

Question 19

What is the simple regression equation?

Answer 19

Y = (B coefficient)x + (intercept)

Question 20

What is the b coefficient (slope)?

Answer 20

How much the outcome variable (Y) changes for each unit of change in the predictor variable (Y)

Question 21

What is R-squared?

Answer 21

It is how much of the variance in the outcome variable is accounted for by the predictor variable

x100 to convert to percentage of how much variation in outcome variable

Question 22

What does it mean if R-squared = 1?

Answer 22

If you are given the value of the predictor you can calculate the exact value of the outcome

Question 23

What does it mean if R-squared = 0?

Answer 23

The predictor is not helpful at all

Question 24

How do we summarise simple regression? (Statistics)

Answer 24

F(df, df) = (F), p = x, R = x, R^2 = x

F = name of statistic

Question 25

How do we summarise simple regression in text?

Answer 25

Plain English telling about statistical significance
Stats
% from R^2 and explain
B coefficient and increase/decrease every…

Question 26

How else can univariate normality be tested other than skewness tests etc?

Answer 26

Visual inspection. Using histograms, box plots and other graphical method such as stem and leaf plots

Question 27

How do we check bivariate normality?

Answer 27

Scatterplots, should be no regions of large empty space and points should be evenly distributed

Question 28

What did Cohen (1988) define a strong correlation as?

Answer 28

One in which the association is clearly vis able to the naked eye

Question 29

What is conditional probability?

Answer 29

A p-value form of probability.

Probability of an event occurring conditional on some other specific situation or event being true