Processing data

Tables

The best way to display collected data is in a table. This helps to organise your data collection.

The following are good guidelines when presenting results in tables:

  • if drawing a table by hand use a ruler and a pencil
  • column headings should show quantity and unit
  • independent variable in the first column and dependent variables in columns to the right
  • all results for a particular quantity should be recorded to the same number of decimal places
  • no units in the body of the table

Example

A student has been investigating how the time for ten swings of a pendulum varies with length. They record the following results:

The table measures lengths against the time taken for ten swings

Length (cm)Attempt 1 (s)Attempt 2 (s)Attempt 3 (s)Average time for ten swings (s)
208.78.89.28.9
4012.612.412.812.6
6015.315.315.515.4
8017.918.017.617.8
10020.019.820.019.9

Significant figures

When doing calculations with measured answers, the answer should have the same number of significant figures as the measured value.

When rounding a number that has more significant figures than are justified, round up if the last figure is between 5 and 9 inclusive, if it is between 0 and 4 inclusive round down.

For example, the number 3.5099 rounded to:

  • 4 significant figures is 3.510
  • 3 significant figures is 3.51
  • 2 significant figures is 3.5
  • 1 significant figure is 4

Charts and graphs

Charts

Charts are a way to display data after it has been collected.

Discrete data can only have certain values and are shown using a bar chart. This can help to show any patterns.

A pie chart shows a category compared with the whole. For example, the percentage of each energy source used in the UK can be shown using a pie chart.

Pie chart showing global energy consumption in 2014.

Graphs

Continuous data can take any value in a given range. It includes time, mass and length.

Continuous data should be presented on a line graph. Line graphs are particularly useful in helping to spot any trends or patterns in the data. For example, the relationship between current and voltage for a resistor.

Graph plotting voltage against current for a fixed resistor. Line is directly proportional.

The following is best practice when drawing graphs:

  • use a ruler and pencil to draw the axis
  • label the axis with the quantity and the unit it is measured in
  • the independent variable should be plotted on the X-axis and the dependent variable should be plotted on the Y-axis
  • use an appropriate scale for your axis - this should lead to a graph that uses more than 50% of the paper
  • when drawing a line or curve of best fit there must be a reasonable balance of plots either side of the line
  • a ruler should be used to draw a straight line of best fit
  • when the data produces a curve, the curve should be drawn smoothly free-hand