Presentation and display of quantitative data
Specification: Presentation and display of quantitative data: graphs, tables, scattergrams, bar charts, histograms.
Graphical techniques and tables are used to summarise data in a clear and visually accessible way.
Tables
Perhaps the most straightforward way of presenting data is in tables, which will summarise the key descriptive statistics for a data set, for example, the mean values and standard deviation values for each condition within a psychological investigation. Presenting data in this way will allow the reader to easily compare the most important values, without needing to interpret the data. For example, the following table outlines the mean scores and standard deviation for Godden and Baddeley’s (1975) study.
Scattergram
A scattergram (sometimes called a scattergraph) is a graph that shows the correlation between two sets of data (co‐variables) by plotting points to represent each pair of scores. It indicates the degree and direction of the correlation between the co‐variables, one of which is indicated on the X‐axis and the other on the Y‐axis.
A positive correlation shows an upward trend whereas one variable increases, so does the other.
A negative correlation shows a trend going in the opposite direction whereas one variable increases, the other decreases.
With a zero correlation, there is no distinct relationship shown between the two variables. The individual participant marks randomly appear on the scattergram.
Bar chart
Bar charts are used to show frequency data for discrete (separate) variables, e.g. used to plot mean scores separately for conditions A and B (and C, D, E…). For example, the following bar chart below demonstrates the results from Loftus and Palmer (1974).
Histogram
A histogram is somewhat similar in appearance to a bar chart, and there is often confusion between the two. The key difference is that a histogram has the bars touching each other, whereas a bar chart has a gap between each. The reason for this is that a histogram is presenting continuous data (e.g. ages 0–9, 10–19, 20–29, etc.). Furthermore, the y axis on a histogram represent frequency whereas on a bar char it represents the value.
Possible exam questions
Name the type of graph which is most appropriate for displaying the results obtained in a correlational study. (1 mark)
Explain the difference between a bar chart and a histogram. (2 marks)
Name two methods a psychologist could use to display quantitative data. (2 marks)