Thinking and Working Scientifically & Laboratory Reference
TWS 4: Drawing Graphs — Bar Charts, Line Graphs, Scatter Graphs & Lines of Best Fit
5 min read 5 parts Lesson 4 of 8
Lesson summary
TWS 4: Drawing Graphs — Bar Charts, Line Graphs, Scatter Graphs & Lines of Best Fit — Alhussan International Academy — Science (Stages 7–9) notes: Choose the correct chart for a variable type and draw a bar chart, line graph or scatter graph with a suitable line of best fit.Categ…
- Categoric variable
- Discrete variable
- Continuous variable
- Fair tests
- Other investigations
- Correlation is not causation
Part 1 of 5Types of variable
- Categoric variablethe values are words with no logical order, such as names or types of metal.
- Discrete variablenumbers with no in-between values, such as shoe size, paper clips in a pot or people in a room.
- Continuous variableit can take any value, such as height, temperature and time.
Part 2 of 5Choosing the chart
| Variables | Best display |
|---|---|
| Categoric or discrete variable | Bar chart or pie chart |
| Both variables continuous | Line graph or scatter graph |
| Fractions of a whole | Pie chart |
| Data that do not add together | Bar chart |
- Limit — bar and pie charts are only for data that include categoric or discrete variables.
Part 3 of 5Pie charts and bar charts
- Pie chart — it shows fractions of a whole, such as who did the most work on a project.
- Bar chart — it is better when the data do not add together to a whole.
- Write the variable you observe on the y-axis with units, and the variable you change or compare on the x-axis.
- Write the y values on the lines, evenly spaced, and start at zero only if values are close to zero.
- Write the x values in the spaces between the lines.
Part 4 of 5Drawing a line graph
- Usea line graph shows the link between two continuous variables, the independent and the dependent variable.
- Axeswrite the dependent variable (observed or measured) on the y-axis and the independent variable (changed or compared) on the x-axis, each with units.
- Scalesnumbers on each axis are evenly spaced, starting just below the lowest value, with intervals that make plotting easy.
- Pointsmark each with a neat pencil cross.
- Line of best fitdraw a smooth line, straight or curved, with equal numbers of points above and below.
- Fair testsfor continuous data from a fair test, a line graph is usually plotted.
Part 5 of 5Scatter graphs and correlation
- Scatter graph — it shows whether there is a correlation between two continuous variables.
- Points close to a straight line mean a correlation.
- If points are scattered all over the graph, there is no correlation.
- Other investigations — a scatter graph is usually plotted to see whether there is a relationship between two variables.
- Line of best fit — it goes through as many points as possible, with roughly equal numbers either side.
- Correlation is not causation — a correlation does not mean one variable affects the other.
- Ice cream sales and swimming-pool visits both rise on hot days, so one does not cause the other.
- Anomalous points — they lie far from the line and are circled and ignored when drawing it.
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