Transforming data

Question 1

How do we know if data are normally distributed?

Answer 1

If non-significant

Question 2

What are the acceptable limits of skewness?

Answer 2

-1 to +1

Question 3

What are the acceptable limits of kurtosis?

Answer 3

-3 to +3

Question 4

What are the four common types of transformations?

Answer 4

Log transformation
Square root transformation
Reciprocal transformation
Reverse score and then apply any of the above

Question 5

What can log transformations do (and not do)?

Answer 5

Correct positive skew, positive kurtosis, and unequal variances
Squashes right tail distribution
Cannot be used directly with 0s or negative numbers

Question 6

What can square root transformations do?

Answer 6

Correct positive skew, positive kurtosis, and unequal variances.
Has greater effect on larger numbers than smaller ones - brings values closer to middle

Question 7

What can reciprocal transformations do?

Answer 7

Correct positive skew, positive kurtosis, and unequal variances

Question 8

What can reverse scoring and applying any of the above do?

Answer 8

Correct negative skew

Question 9

How do you do a log transformation on SPSS?

Answer 9

transform -> compute variable
- new variable name in target box
function group - select arithmetic
functions and special variables - Lg10 - move to numeric expression box
Move variable you want to transform to Lg10()

Question 10

How do you do a square root transformation in SPSS?

Answer 10

transform -> compute variable
new variable name in target box
- function group - arithmetic
- functions and special variables - Sqrt - double clock and move to numeric expression
- move variable you want to transform to Sqrt(?)

Question 11

How do you do a reciprocal transformation on SPSS?

Answer 11

transform -> compute variable
new name in target variable box
- type 1/ in numeric expression box
- move variable you want to tranform into the box

Question 11

How do you reverse score (and then apply any of the above) in SPSS?

Answer 11

transform -> compute variable
New variable name in target box
- Identify highest value for variable to be transformed in dataset - type into numeric expression box followed by a minus sign.
Move variable you want to transform to the box
- Can then apply another transformation to this reverse scored variable