Using controls

Dr Ravi Gooneratne (Lincoln University) describes several ways in which he uses controls in the experiments on soil pollution that he carries out. A good control enables him to be certain the effect he observes is a true effect rather than one caused by an outside influence such as temperature. Controls are very important in any experiment.

Transcript

DR RAVI GOONERATNE We have a worm colony – it’s basically a bucket with soil from a farm where they have not used pesticides for a long, long time, so we know that this soil is fairly clean and without any pollutants. We have collected worms and we feed them with grass meal and dried cow manure and they reproduce. In my lab, we standardise earthworms, and we use them anything between 8 weeks and 12 weeks. The worms that we add to polluted soil, we take a basal measurement and then put them into soil. Strictly speaking, they themselves act as their own controls. So I take a reading today of this in the polluted soil and tomorrow it might decrease, and when I measure the control, it also might also decrease. It could be a cold day, so in order to compensate for changes in the environmental conditions, we use control animals as well with each experiment. In scientific data, you’ve got to basically show that any findings you have, they need to be statistically significantly different from the controls, and that’s why, you know, we use six control worms and we put about another six worms in the polluted soil. We have one worm in each bottle so they are all separate although they are in the same soil. So basically we look at how much the worms in the polluted soil change compared to the change we see in the control worms.