1. Displaying data
Seminar 2

2. Today’s Question
Once we have collected a large number of measurements, how can we summarize or describe those measurements most effectively by using visual techniques?

3. Conveying Summary data
Part 1
Conveying Summary data

4. Pie Charts
Pie charts are commonly used to represent scores that have a fixed total (e.g., 100%) – that’s why it’s a full circle
Here, income spent on necessities.
Rarely used in psychology research. Why?

5. Barcharts The same pie chart can be translated into a barchart
But barcharts do not assume that there is a fixed total.
Hence, a barchart does not necessarily convert back into a pie chart.

6. Line graphs X-axis: usually, but not always, a continuous variable
Any differences in interpretation between the two graphs?

7. Scatterplots X-axis: almost always continuous variable
A line of best fit is usually added
Very useful for inspecting outliers

8. Let’s take a look at Excel
Advantages
Hi-resolution graphics tool
Easy to use
Disadvantages
Cannot plot broken axes
Plotting of error bars is complicated
No histograms (you need to install the Add-On Data Analysis Toolpak)

9. What does Excel offer?
You probably need only three: column, line & scatter

10. WARNING: Never plot 3D graphs

11. Conveying Distributional information
Part 2
Conveying Distributional information

12. An Example How can you create some order in the chaos?
How stressed have you been in the last 2 weeks?
Scale: 0 (not at all) to 10 (feels like exploding)
How can you create some order in the chaos?

13. Frequency Tables
A frequency table shows how often each value of the variable occurs
Stress rating
Frequency 10 14 9 15 8 26 7 31 6 13 5 18 4 16 3 12 2 1

14. Frequency Polygon Stress rating Frequency 10 14 9 15 8 26 7 31 6 13 518 4 16 3 12 2 1

15. Histograms
Another way of visually representing information contained in a frequency table
Histograms are like bar charts; bars are used instead of connected points
The bars typically cover “intervals” (also called “bins”) of values.
The first bar here covers scores > 0 and < 1.

16. Shapes of Distributions
These representational aides all describe frequency distributions: the way score frequencies are distributed with respect to the values of the variable
Distributions can take on a number of shapes or forms

17. Unimodal Distributions
The mode of a distribution refers to the most frequently occurring score
Mode = “peak”
In a unimodal distribution, one score occurs much more frequently than others

18. Multimodal Distributions
In multimodal distributions, more than one mode exists (or approximately so)
In a bimodal distribution, two modes exist
What will cause a bimodal distribution?
Note: This is not a binomial distribution

19. Rectangular or Uniform Distributions
In a uniform distribution, all values are observed equally often

20. Question Suppose you throw a dice.
What will the shape of the distribution of the numbers be?
*** Hint to Tutorial 4 ***

21. Symmetrical and Skewed Distributions
A symmetrical distribution is balanced: if we cut it in half, the two sides would be mirror images of one another
Normal distribution: a particular kind of distribution that resembles a bell (bell-shaped distribution)

22. Skewed Distributions
A skewed distribution is unbalanced; there may be a cluster of scores piling on one end of the scale

23. Question: What are some possible reasons causing skewed distributions?
negative skew
positive skew
Question: What are some possible reasons causing skewed distributions?

24. Boxplots
An efficient way to display five attributes: minimum non-outliers, lower quartile, median, upper quartile, maximum non-outliers
More in Seminar 3

25. Boxplot conveys even more information!
What does it convey?
__________

26. Part 3
Tables

27. Why use tables?
Efficient presenting simple lists (e.g., demographic characteristics)
But can be difficult to comprehend (any solutions?)
Chan et al. (2012). What do love and jealousy taste like? Emotion.

28. Contingency tables
A matrix format that displays the data (e.g., frequency or mean) of the variables
This is a 2 (Sex: male vs. females) x 2 (Handedness: right vs. left) contingency table
Right-handed
Left-handed
Total
Males 43 9 52
Females 44 4 48 87 13
100
Marginal totals/means
Grand total or mean
Marginal totals/means

29. What makes a good or bad graph?
Part 3
What makes a good or bad graph?

30. Your task Get into groups of about 5.
Identify any problems with the following graphs.
Devise a solution.
Think whether your solution creates other problem(s).

35. Nummenmaa et al. (2014). Bodily maps of emotions. PNAS.

36. World Bank (2015). World development indicators.

37. Take home messages
Graphs should be minimally simple (even colors should be avoided – why?)
Plots communicate information easily
But sometimes tables do a better job.
Think of what you want to communicate, and think of what readers will interpret your data.