# Observation and measurement skills

## Key points

• Calculating from data is usually more accurate than using just one result.
• Choosing the correct range and intervals for recording data is important in order to reach valid conclusions.
• Recording data in a table ensures that data is recorded in an organised way.

What should you draw before an experiment to organise your results?

A results table.

### Video

Watch this video about collecting data during an investigation.

## Calculating averages

In maths, there are three types of : the , and .

In science, the mean is used most often.

To calculate the mean, follow these two steps:

1. Add up all the results.
2. Divide the total by the number of results.

For example, to find the mean of 8, 6, 12, 3, 11:

1. Add up all the results: 8 + 6 + 12 + 3 + 11 = 40
2. Divide the total by the number of results: 40 ÷ 5 = 8

There are five results that add up to 40, the mean of these results is 8.

In science, the mean is usually calculated from . The mean of the readings is usually more than simply using one of the results. An accurate reading is one that is close to the . By calculating a mean, it helps reduce the effect of that may otherwise make a result .

When calculating a mean, watch out for . Outliers are not included when calculating the mean. For example, if an experiment times how long it takes for a model car to travel a distance and the results are 38, 38, 48 and 39 seconds, it is likely that the third result of 48 seconds is an outlier. It should not be included in the calculation of the mean. If the experiment was still being carried out, it should be repeated and that result used instead.

Calculate the mean of 29, 29 and 32.

The mean is 30.

1. Add up all the results: 29 + 29 + 32 = 90
2. Divide the total by the number of results: 90 ÷ 3 = 30

## Choosing intervals for recording data

Scientists collect data to answer questions. Data can be or .

• If the data is quantitative, choose the of data carefully.
• If this is too narrow or too wide, then some patterns might be missed when .

The following should be considered when choosing for recording data:

• The range of data should be as big as possible, without damaging the , eg overstretching a spring.
• Once a range has been chosen, choose intervals within the range and decide what measurements to take.
• Splitting the range into equal intervals is a good way of getting a spread of measurements that will help give good quality data. For example, if an experiment was to be carried out over five minutes, taking a reading every minute would be a good idea.

During an experiment, measurements are usually repeated. When this is done, the data should be similar. The data is .

If other people did the same investigation they should get similar data. The data is .

During an investigation into how quickly water cools over 30 minutes after being boiled, what interval should be chosen for taking readings?

A time interval chosen between three and six minutes would be sensible.

Any longer would not give many readings, any shorter would give more readings than would probably be needed.

## Drawing and using a results table

Putting information into a table can make it easier to read and understand.

Draw the table before starting the experiment and include the following information:

• A heading in each column - include units if appropriate.
• The in the first column.
• The in the other column.

Use a ruler and a pencil to draw the table .

During experiments, data is collected and recorded in a table. Collecting data involves using equipment and taking readings. For example:

• Measuring the time taken for something to happen using a stopwatch.
• Using a ruler to measure the height that an object has bounced.

As well as the heading, what else may need to be included at the top of each column?

Units.

## Communicating science in a table

Ordering data in a table is helpful in making the information clearer. Tables can be used to present quantitative data, qualitative data and to compare different things.

If the independent variable is a number (quantitative data), they are often written in order from lowest to highest in the first column:

Mass (g)Length of spring (cm)
10
20
30
40
50

If the independent variable is a word (qualitative data), a table may be used to help spot a pattern. For this reason, sometimes the data is best ordered using the dependent variable:

Method of travel to workNumber of staff members
Car34
Train21
Bike16
Walk10

A table can be used to compare different things. When doing this, each row should present information that is similar or different about two things:

AcidsBases
Taste sourTaste bitter
Turns indicator paper redTurns indicator paper blue
pH less than 7pH more than 7
Conducts electricityConducts electricity

When the independent variable is qualitative, the data can be ordered using which variable to help spot a pattern?

The dependent variable.