Statistics/Displaying Data/Bar Charts
Bar Charts
[edit | edit source]The Bar Chart (or Bar Graph) is one of the most common ways of displaying catagorical/qualitative data. Bar Graphs consist of 2 variables, one response (sometimes called "dependent") and one predictor (sometimes called "independent"), arranged on the horizontal and vertical axis of a graph. The relationship of the predictor and response variables is shown by a mark of some sort (usually a rectangular box) from one variable's value to the other's.
To demonstrate we will use the following data(tbl. 3.1.1) representing a hypothetical relationship between a qualitative predictor variable, "Graph Type", and a quantitative response variable, "Votes".
tbl. 3.1.1 - Favourite Graphs
| Graph Type | Votes |
|---|---|
| Bar Charts | 5 |
| Pie Graphs | 2 |
| Histograms | 3 |
| Pictograms | 8 |
| Comp. Pie Graphs | 4 |
| Line Graphs | 9 |
| Frequency Polygon | 1 |
| Scatter Graphs | 5 |
From this data we can now construct an appropriate graphical representation which, in this case will be a Bar Chart. The graph may be orientated in several ways, of which the vertical chart (fig. 3.1.1) is most common, with the horizontal chart(fig. 3.1.2) also being used often
fig. 3.1.1 - vertical chart
fig. 3.1.2 - horizontal chart
Take note that the height and width of the bars, in the vertical and horizontal Charts, respectfully, are equal to the response variable's corresponding value - "Bar Chart" bar equals the number of votes that the Bar Chart type received in tbl. 3.1.1
Also take note that there is a pronounced amount of space between the individual bars in each of the graphs, this is important in that it help differentiate the Bar Chart graph type from the Histogram graph type discussed in a later section.