Graphing Data

Navigate the knowledge tree: 🌿 Biology ➡ NCEA Level 2 Biology ➡ 2.1 Investigation ➡ Lesson 8: Grahing Data

Learning Intentions

By the end of this topic, you should be able to:

Choose the right graph for my data.
Plot data clearly and accurately with correct labels, scales and units.
Spot patterns or trends in my graph.
Describe what a graph shows using scientific language.

Glossary

Key terms and definitions.

word: Definition

How to choose which type of graph is suitable

Choosing what charts or graphs to draw is influenced by the nature of the data. There are many different types of graphs, and different graphs are appropriate for different kinds of data. Before representing data graphically, it is important to identify the kind of data you have.

For continuous data:
- - scatter plots (visualise relationship between variables)
  - line graphs (visualise trends over time)
  - histogram (visualise distribution)

For continuous data with calculated means, points can be connected. On scatter plots, a line of best fit is often drawn.

For categorical data:
- - box plot (visualise distribution)
  - bar graphs (visualise trends over time, better than pie chart)
  - pie chart (only use for few categories, great for communicating with the public)

This is an excellent video that clearly distinguishes between the different types of data and which graphs to choose to represent different types of data.

Guided practice

For each investigation, choose the correct graph type.

Sugar concentration (M) vs average % change in mass of kumara
Type of vegetable vs average mass change
Time (minutes) vs rate of diffusion

Answer:

Line graph - Sugar concentration is continuous numerical data with an order.
Bar graph - Vegetable type is categorical data (names, not numbers).
Line graph - Time is continuous numerical data and shows change over time.

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Presenting graphs properly requires attention to a few basic details, including:

Use graph paper and a ruler.
Put the independent variable on the horizontal (x) axis, and label both axes with the name of the variable and the unit.
Make sure the scale on the axes shows a good range based on your results.
Give the graph a descriptive, accurate title.
Take care with accurately plot the points, using crosses 'x'.

Step 1: Determine the axes

A graph has two axes drawn at right angles:

The horizontal axis (or x-axis) along the bottom for the independent variable.
The vertical axis (or y-axis) up the side for the dependent variable.

Step 2: Label each axis

Each axis has a label. The axis label shows the name of the variable and its unit. The usual convention is for the units to be enclosed in brackets.

Step 3: Add the tick marks

On each axis, there are tick marks (the little marks at regular intervals along each axis. There are also tick mark labels (the numbers next to the tick marks).

Step 4: Plot the data points

The data points are the values plotted on the graph. Each point is plotted using a pair of values for the variables (the x-coordinate and the y-coordinate).

Step 5: Draw the line of best fit

A line is drawn, which either connects all of the data points or is a line of best fit. A scatter graph may show just the data points or it may also have a line of best fit.

When scientists are trying to determine whether there is a relationship between two variables, it can be helpful to draw a graph and use a line of best fit, or trend line.

In many experiments, you cannot draw a line that passes through all the points. You have to draw a line that fits most of them. This is called the line of best fit.

Step 6: Write a title

Finally, a graph should have a title that describes what the graph is showing. If there is more than one line on the graph, there will also need to be a legend or key to show what each line represents.

Guided practice

You measure a kumara piece and record its mass as 6.2 g. Your partner records the same piece as 6.237 g. Which measurement is better, and why?

Answer: The measurement 6.237 g is better.

It is more precise because it records more decimal places. As long as the balance allows this precision, it improves accuracy and consistency across data.

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Glossary

Key terms and definitions.

word: Definition

Practice Tasks for Different Thinking Skills

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