• Question: how do you know when your science experiments hasn't work right?

    Asked by ccraig11 to Joe, Juan, Kate, Rory, Rosie on 12 Mar 2014.
    • Photo: Rory Miles

      Rory Miles answered on 12 Mar 2014:

      In my work we use things called quality controls to ensure that the particular experiment has worked. These are just samples that have an amount of the particular microbe at a level that we know they have. I generally run a positive control with each experiment , this is just a sample that actually contains the microbe. This should be positive in each of the experiments I run, otherwise I can’t be certain that my experiment can detect the microbe. I also run something called a negative control. This does not contain any microbes and should be negative in all experiments. If this is positive in my experiment, it could mean that there is a microbe affecting my experiment and my results may be very wrong. If I did not use things such as quality controls in my experiments, my results would not mean very much and there would be no way of knowing if they were correct.

    • Photo: Juan Carlos Lopez-Baez

      Juan Carlos Lopez-Baez answered on 13 Mar 2014:

      Simple…if it doesn’t give me the result that I want then it has DEFINITELY not worked! 😛

      No, actually, in reality is not as simple as that. As Rory has so rightly said, the best way to tell is by having controls. The controls will always tell you if things have worked or if things have gone wrong. There are two types of controls that you can have, a positive control and a negative control and I think the best way to explain them is by using an example:

      Imagine that you have a glass with a powder inside that you know it is either sugar or salt. In your experiment you want to find out which one of the two it is, so you are going to add water and taste it. Because you want to know how sugar with water and salt with water taste, you will add sugar to another glass and salt to another and add water to each one of them. These will be your positive controls, as they will tell you how either of them should taste in water. You also want to make sure that the water does not taste sugary or salty, so in another glass you are going to have the water by itself and you are going to taste it to make sure it does not taste of anything. That will be your negative control. Now, you can go ahead and mix the unknown powder with your water and taste it and find out for sure whether it is sugar or salt. Of course, if it doesn’t taste of either of them, then you know that something has gone wrong and it has not worked, so you need to repeat it again 🙂

      (our experiments are a bit more complicated than this, but the principle is basically the same)

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