When you have obtained results from your experiment or investigation, you then need to process them. In most investigations, you will have obtained a set of numbers as the results. One way to process these is to calculate the average value. There are three main types of average: median, mode and - the subject of this GCSE Biology quiz - mean.

It is always a good idea to repeat your experiment several times in order to get a larger amount of data. Once who have gathered enough data you can then calculate the **mean value**. The mean is one particular type of average. To calculate the mean you add up all the values and divide by the number of values in your sample (the sample size). When you work out the mean of a set of results, it is particularly useful as it '*smooths out*' the results and gives a more reliable overall answer.

Imagine that you have carried out an experiment looking at how temperature affects the growth of seedlings. Genetics can affect how quickly an individual plant will grow. The temperature might be slightly different for some seedlings too. The result would be that some grow more slowly than others. So to overcome these sources of error in your investigation, you should have planned to use a large number of seedlings and to measure the mean height. This ensures that no single seedling will influence the results so they will be more accurate and reliable. To get the most reliable results, you would need to use a large number of seedlings, the more you use, the better the mean will be.

The mean is one of the three most common types of **average**. The others are the median and the mode. The mode is the number that occurs most frequently in your data set and the median is the number that is at the centre of the list when it is written in order. If scientists talk about an average, the almost certainly are referring to the mean. So if you refer to the mean as the average in your exams or investigation, don't worry, you won't be penalised!

1.

What is the median for this data? 11, 11, 12, 13, 15, 19, 21

11

12

13

21

The median is the middle value. The 4th number in the list of 7 numbers in ascending order

2.

To calculate the mean, we divide the sum of the results by the...

average

sample size

range

statistic

Larger sample sizes give more reliable results

3.

Find the mean of the following data: 4, 6, 9, 3, 6

5.4

5.5

5.6

5.7

Sum then divide by the sample size

4.

The sample size is the...

range

number of results

mode

graph

You only need a sample size of two to calculate the mean

5.

What is the mean for the values: 13, 18, 13, 14, 13, 16, 14, 21, 13

15

16

17

18

Two thirds of the numbers are less than the average, this shows you how you need to be careful. In an experiment, the values of 18 and 21 could be anomalous results and may need re-checking for accuracy

6.

Mean is also known as the...

mode

median

average

range

Average is a general word that includes the median and the mode so if you are stating that you are going to work out the average value, strictly speaking you would need to specify which one you intended to use

7.

Average can never be the same value as the maximum unless it is ...

the mean

the minimum

the mode

the median

The other types of average must be less than the maximum

8.

The mode is...

the same thing as mean

equal to the average

the number that is repeated most often

the middle value

In some cases, you would be more interested in the mode than the mean

9.

What is the mode for this data? 11, 11, 13, 13, 11, 14, 11, 11, 12

11

12

13

14

It is the most common number in the data set

10.

We can use the mean values of a set of results to ...

plot a scatter diagram

write a hypothesis

draw the diagram

write a risk assessment

Adding a line or curve of best fit then shows the correlation between the variables that have been investigated