Lecture 18 - Graphing Data

Question 1

What graphing method is best for categorical data frequencies?

Answer 1

Histograms and percentage histograms.

Question 2

What graphing method is best for binned numerical data?

Answer 2

Histograms and cumulative histograms.

Question 3

When should error bars be used?

Answer 3

Whenever a mean of several measurements is displayed.

Question 4

What do error bars indicate?

Answer 4

The variability or confidence interval for a data point.

Question 5

How is using error bars different between SPSS and Excel?

Answer 5

In SPSS, they are a type of plot, whereas in Excel they can be added to a graph.

Question 6

What values can be used for error bars?

Answer 6

SD, SEM & CI

Question 7

What source of variability are error bars often associated with?

Answer 7

Inter-subject variability, but not necessarily - can be the biggest source of noise in an experiment.

Question 8

When doing an error bar plot on SPSS with multiple IVs and a within-subject design, which options should be selected on the menu?

Answer 8

Clustered and ‘summaries of separate variables’.
For one IV - simple.
For a between-subject design - ‘summaries for groups of cases’.

Question 9

In SPSS, what is the default setting for what the error bars represent?

Answer 9

95% CI.

Question 10

When are scatter plots useful?

Answer 10

When there are several levels for an IV.

Question 11

How do you add a line of best fit to a scatterplot in SPSS?

Answer 11

Click on a data point, goes blue, then Chart|Add Chart Element|Fit Line at Total.

Question 12

How do you overlay additional data on a scatter plot in SPSS?

Answer 12

Graphs/Scatter/Overlay

Move 2 variables over at once for an x-y pairing.

Question 13

How do you create a transform of some original data in SPSS?

Answer 13

Transform/Compute

Insert correct variable and enter appropriate equation, e.g. for a z transform.

Question 14

How should multidimensional data be grouped?

Answer 14

However is appropriate given what you want to show. E.g. looking for gender differences or task improvement?

Question 15

What is a con of 3-D bar plots?

Answer 15

It is difficult to see items at the back, especially if they’re smaller than bars in front.

Question 16

What’s the problem with presenting multidimensional data in a surface plot?

Answer 16

They require elaborate plotting packages.

Question 17

What different kinds of surface plot can be used to represent multidimensional data?

Answer 17

Mesh plot (grid-like)
Mesh combined with intensity (grid-like and colour grading)
Surface with intensity and contours (lines and colour grading)

Question 18

What medium is a popular way to represent intensity?

Answer 18

Colour.

Question 19

What is a problem with using colour to represent intensity?

Answer 19

It can potentially introduce effects that aren’t really there, e.g. identical MRI data painted with different ‘colour maps’ and thresholding can look very different.

Question 20

How is it possible to represent four dimensional data?

Answer 20

Using a movie

Question 21

What is the problem with 4-D data?

Answer 21

It’s so confusing that it’s probably better to devise a simpler experiment.

Question 22

What should you do before plotting a graph?

Answer 22

Decide the key points to be conveyed and what you want to focus on.