How Science Works Conducting a Fair Test © SSER Ltd.

What is a Pilot Test? A pilot test is a trial run of an experiment on a smaller scale. Why do you carry out a pilot test before an experiment? Pilot tests enable you to: Check that the experiment works Check that the equipment is properly set-up Identify the range of values for the independent variable Identify any control variables (key variables) that you may not have considered Consider all safety issues involved in the experiment

Pilot Test - Example When yeast is added to a solution of glucose, carbon dioxide is produced. Press the buttons to see how the different amounts of glucose in the solution, affect the volume of gas produced...

“Carrying out a pilot test will allow you to determine...” Pilot Test - Example “Carrying out a pilot test will allow you to determine...” The volume of water used to make up the solution The mass of glucose The mass of yeast to use The temperature at which to carry out the investigation The range of the independent variable The size interval of the independent variable

Fair Testing

variable and to no other factors.” What is a Fair Test? “A fair test is where you ensure that results are due to the effect of the independent variable on the dependent variable and to no other factors.” “You achieve this by ensuring that all the variables other than the independent variable are kept constant or controlled.”

Identifying Control Variables The following apparatus is used to investigate the effect of glucose concentration on the rate of yeast respiration. Glucose concentration is the independent variable, and the volume of gas produced is the dependent variable...

Identifying Control Variables Identify the control variables that you would need to keep constant during the experiment, to ensure a fair test. Move on to the next slide to show the variables…

Identifying Control Variables “To be sure that changes in the volume of carbon dioxide produced are due to changes in glucose concentrations, you would have to ensure that the following control variables were kept constant…” The volume of glucose solution The mass of yeast The temperature of the reactants The age and species of the yeast

Identifying a Fair Test For these investigations, identify the experiment which would give a fair test…

Fair Testing Outside a Laboratory It is considerably more difficult to control variables when investigations are conducted outside a laboratory. Students measuring a popular footpath in the New Forest However, for the collected data to be valid, every attempt to control all but the independent variable must be made. This means that any variables that change their values must do so in the same way for all the measurements taken of the dependent variable.

Fair Testing Outside a Laboratory “How does fertiliser affect the growth of French beans?” An investigation such as this is likely to be carried out in the environment. Using the same test site for the entire experiment enables you to control aspect, altitude, soil type, temperature, rainfall, light levels and wind.

Fair Testing Outside a Laboratory “How does fertiliser affect the growth of French beans?” In this way, each batch of French beans receives the same environmental conditions. The only variable you will change will be the amount of fertiliser you add to the soil - the independent variable.

Fair Testing and Human Subjects Fair testing is also quite difficult when the test subjects are human beings. New drugs are often tested on human subjects. These tests have to be carefully controlled.

How could you test these claims scientifically? Before After How could you test these claims scientifically?

Controlling Clinical Trials Investigation: Assess the effect of a new dietary supplement which claims to aid weight loss in human beings. In this investigation, the independent variable is the new drug and the dependent variable is weight loss. If you simply gather together fifty people who want to lose weight, and offer them the chance to take part in a controlled clinical trial, the data you collect will not be valid. You need to control a whole range of variables before you start, such as... Gender General health Smoking/non-smoking Age range Ethnic background Prescribed medication Starting weight Diet Physical activity

Clinical Trials and Placebos Having selected your volunteers, you will divide them into two equal groups. One group will be given the new dietary supplement, the other group will be given a placebo - a tablet containing no active ingredients at all. The second group act as a comparison group. Clinical trials are usually carried out blind. This means that neither the subjects nor the doctor know who is taking the drug, and who is taking the placebo. (Often referred to as double-blind testing). This is a very difficult area in which to control all the variables as people behave and react differently. Sometimes people taking the placebo notice improvements - this is known as the placebo effect.

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