Processing & Presenting Data

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Finding an Average

Glossary

Key terms and definitions.

Processing Depends on Type of Data

After you have completed your experiment, the data need to be organised and displayed. Doing this makes it much easier to identify trends or patterns in the data. It also helps to identify any relationships that result from cause and effect between the independent and dependent variables. Has one variable had any effect on the other variable?

The best way to display results depends on whether the data is qualitative or quantitative.

Qualitative data usually refers to the physical characteristics of a substance or object and may be recorded in a diagram or in a sentence, e.g. the colour of a product made in a chemical reaction, the shape of crystals made by cooling a saturated solution, where starch is present in a leaf.
Diagrams should be fully labelled and detailed descriptions completed using correct scientific terms.
Quantitative data can be measured or counted and recorded as numerical information in a table and graph, e.g. the speed of a trolley, the temperature of a liquid, the time a reaction takes.

More on Processing Data

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Glossary

Key terms and definitions.

Data Tables

Measurements or observations are called data. The best way to record data in a form that is easy to understand is to use a data table. Data tables can also squeeze in a lot of information into a small space.

Tables provide an accurate record of the numerical values and allow you to organise your data.

Columns must have headings that show what the variable is and the units it is measured in.
The first column will show the independent variable, e.g. the force used to push the trolley.
The next columns are where the data you measured (the dependent variable) is recorded, e.g. the time the trolley took over 1 m.
If the experiment is repeated several times, the result of each trial (raw data) is recorded and then the calculated mean or average (processed data) is recorded.
Other processed data is also put in the table, e.g. calculations of the speed of trolley.

Questions

Look at the table of the trolley journey and explain:
1. - Which results are raw data and which are processed data?
  - Explain in your own words what 'raw data' means.
On some graph paper, draw a speed-force graph on the results for the trolley investigation.
Write down what sort of information is easier to see on a graph than in a table.

Graphs

Graphs are a very useful way of presenting numerical data visually to display any patterns or trends that may not be visible from a table. It makes it easier to see patterns and trends so you can describe the relationship between the independent and dependent variable.

Whether you draw a line graph, a bar graph, a histogram or a pie chart will depend on the data collected. When both variables have discrete values, as in the trolley example, a line graph is used. Remember the rules for drawing a line graph:

Use graph paper.
Put the independent variable on the horizontal (x) axis.
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 title.
Use a small x to plot the data.
Use a line of best fit through the crosses

Remember:

To show discrete data, join the points with a ruler.
To show mathematical relationships, join the points with a single smooth line, called a trend line or a liine of best fit.

Different types of graphs are used, depending on what you are trying to show:

Line graphs, for showing how one gariable changes comared to another, e.g. temperature and time when water is heated.

Bar graphs, for unrelated information, e.g. numbers of birds of different types in a forest.

Histograms, for related information, e.g. numbers within certain ranges of height.

Pie graphs, for showing percentages, e.g. percentage of people with different blood groups

More notes:

A line graph is not the only type of graph you can use to record results. In a column graph, the columns run vertically, or up and down the page.

In a bar graph or chart the bars run horizontally, or across the page. These graphs are used to compare groups of things. For example, if you wanted to record the types and numbers of cars that go past the school gate in a half-hour period, you would use a column or a bar graph.

Using both Tables and Graphs

It is usually appropriate to include a table and a graph in your final scientific report.

For example, many experiments (like the one below) involve measurements that are recorded at set times. These are best shown in tables and graphs. The mass is being recorded every minute, and the results are shown in the table and on the graph shown below.

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.

Questions

Write up the following experiment using the correct headings, and show the results as:
1. - a chart
  - a graph
    
    Some students wanted to see if crushing the marble made it react faster with acid than the marble chips did. They added acid to crushed marble and recorded the initial mass as 50 g. They then recorded the following masses at 1-minute intervals: 49 g, 48 g, 47 g, 46 g, 45 g, 44 g, 43 g, 42 g, 41 g, 40 g. The students decided that crushing the marble did make it react faster, because at the end of 10 minutes, the mass of the acid plus crushed marble had decreased by 10 g, whereas the mass of the acid plus marble chips dropped only by 4 g.
In the marble experiment, if the mass stopped changing, what might that mean?
The marble bubbles as it reacts and loses mass. Where does this mass go?

Line of Best Fit

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.

Questions

Why do you think that lines on graphs do not always go through all the points?
What pattern do you see in the results of the graph to the right?
Describe the relationship between the input variable and the outcome variable ont he graph to the right.