How to plan experiments
In a nutshell
Planning an experiment involves considering the variables, the type of data, the equipment to be used and the risks posed. This is all included in the method which is a written summary including all of this, in enough detail for this experiment to be repeated and for results to be replicable.
Planning steps
A well-planned experiment will contain the following key elements:
Element | Explanation |
| Aim
| What is the aim of the experiment i.e. what would you like to find out? |
Variables | You should identify the various variables (independent, dependent, etc) which will effect your experiment. |
| Data | What data will you collect? |
| Equipment | What equipment will you need to get accurate and precise results? |
| Risk assessment | What safety precautions are needed? |
| Method | A detailed method should be written. |
| Tests | Tests are carried out to gather evidence to answer your aim. |
Variables
The two main types of variables are independent and dependent. An independent variable is a variable that you change during an experiment. The dependent variable is the variable which is measured.
Example
You are conducting an experiment on how the amount of water used to water a plant affects growth.
- the independent variable is the amount of water you pour on each plant
- the dependent variable is the size of the plants
Data
Data collected can fall into three categories, discrete data, continuous data and categoric data. It is important that the data collected is suitable for your experiment.
Discrete data
Discrete data is data which can be counted.
Example
The number of children in a room. The values are countable.
Continuous data
Continuous data is data which can have an infinite value.
Example
The time taken for an event to occur.
Categoric data
Categoric data fall into distinct categories or groups.
Example
The colour produced by test-tube reactions.
Equipment
Suitable
The equipment must be appropriate for the aim of the experiment.
Example
You are conducting an experiment on temperature change throughout the night. The apparatus must be able to measure and store temperature information at regular intervals.
Correct size
The equipment needs to be the correct size for the experiment.
Example
You are collecting data on the amount of liquid which falls through a new type of filter. Your flask must be bigger than the total amount of liquid poured over the filter to make sure you are able to collect all the liquid which is poured.
Precision
The equipment is required to have an appropriate amount of precision.
Example
You are adding 1.5cm3 of a liquid to each test tube, it is more precise to use a pipette graduated to the nearest 0.5 cm3 than a pipette graduated to the nearest 1 cm3.
Risk assessments
A risk assessment must be carried out to identify the dangers in the experiment, who they pose a risk to and how to reduce risk.
Methods
The method will take into account all of the above and is written in enough detail, so that someone else could follow the same experiment and produce the same results. The method should include detail on amounts/volumes used, how variables were controlled, the apparatus used and how the risk assessment was actioned. The method should also include information on what data is to be collected and exactly how this is collected.
