Ten Common Graphs and Data Tables on Numeracy Tests
A bar chart looks a bit like the skyline of a city with lots of skyscrapers. (They can also be sideways-on, so they look like a picture of a skyline with skyscrapers going sideways.) Each of the skyscrapers (bars) represents a group or a category – say, the number of people with green eyes or the percentage of late trains in a particular month.
Multiple bar charts
A variation on the simple bar chart is the multiple bar chart, one of the ugliest graphs known to science. The difference between the multiple bar chart and the regular bar chart is (unsurprisingly) the number of bars.
The idea of a multiple bar chart is to compare similar information in two different scenarios – a school’s inspection rankings in two different years, the distribution of ages of the populations of two different cities or the difference between students’ mock and actual exam scores.
A pie chart gets its name because (surprise, surprise) it looks like a pie – a circle divided into slices of various sizes. It shows you at a glance which groups among the data are the biggest and smallest, and the size of the angle at the point of each slice tells you how big the group it represents is.
The three things you may have to do with a pie chart in a numeracy test are to convert between the angle and the size of each group, percentages and the size of each group, and the angles and percentages.
A line graph shows how one quantity responds to changes in another – often, but not always, time. A line graph might show how prices change over time, the expected weight of a cow given its size or how fast a chemical reaction takes place as you change the concentration of one of the ingredients.
Reading a line graph is simple and (hopefully) fairly obvious. You’re normally given one value (say, the time) and have to find the other (say, the temperature).
Multiple line graphs
You may be given a graph with several different lines on it. Multiple line graphs can be confusing, even for the pros, but they’re not too bad if you can keep your head. All you have to do is make sure you’re looking at the correct line – the graph will have a key beside it telling you which graph is which.
A scatter graph is quite similar to a line graph except that it doesn’t usually have a line on it! Instead, it has many dots or crosses. Each mark on the graph represents one thing – for example, a person or an experiment; its position on the graph shows you two values associated with it.
Box plots are part of the teacher training numeracy tests, but not any of the other numeracy tests. A box plot, also known as a box and whiskers plot, looks a little bit like a syringe. It gives you information about the distribution of a data set. In particular, it tells you about the highest and lowest values, as well as the median and the quartiles.
You may see box plots going from left to right or from bottom to top (see Figure 8-7 for an example of each); in either case, they work the same way: you have a box in the middle of the graph with a line in the middle, and two whiskers at the ends of the box, each with a line at the end.
Cumulative frequency graphs
Cumulative frequency graphs are part of the teacher training numeracy tests, but not any of the other numeracy tests.
The word cumulative comes from the same root as accumulate, which means ‘to build up’. A cumulative frequency graph shows how many people or objects have a smaller value than the number on the horizontal axis.
The idea of a two-way table is to show the numbers of observations split across two separate categories and (importantly) the totals of each.
You can see that the bottom number in each column (in the row marked ‘total’) is the sum of the numbers above it, and the last number in each row (in the column marked ‘total’) is the sum of the numbers to its left.
A tally chart is something you might use to record data – for example, if you were doing a survey on Internet browsers or recording different types of plant life in a forest.
You don’t need to know how to make a tally chart for a numeracy test, but you do need to be able to read it.