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Science Survival Kit: Experimental Design

Science Survival Kit: Experimental Design


What do you have to keep in mind when you
are planning an experiment? First of all, don’t forget your scientific
question and the hypothesis. This means you have to think about the two variables – the independent variable and the dependent variable. For the independent variable, consider in which ways you can change it. For the dependent variable, consider how you will observe it and quantify it. And finally for all other parameters, make sure you keep them constant. Next, think about the scales on which you
think that your phenomenon will happen There are two crucial scales to keep in mind
– the time scale and the space scale. For the time scale, consider how fast do you think that the change you are trying to observe is happening. Will it will it be fast (will it take maybe minutes, seconds or miliseconds?) or will it take a long time (days, weeks or maybe even years)? For the space scale, do you think that the change you are expecting to see will occur on a micro-scale (in milimeters or micrometers) or will it happen on a larger scale such as meters or kilometers Thinking about this in advance will help you
choose the appropriate experimental approach. It’s very important that you plan your experiments ahead of time, to try to estimate how long they will take. Of course it’s very hard to do in the beginning when
you don’t have a lot of experience, but try to estimate how long will each step of
the experiment take. Make sure you take into account the replicates of the experiment that you need to make, as well as the repetitions of the experiment. Replicates and repetitions are here to help us reduce the errors in measurement, which might be coming from the imprecision
of the devices we are using, biological noise, or human error. Every experiment needs to have controls. Controls are there to help us know if
the chosen experimental setup is actually suitable for the experiment we are trying to do. There is two types of controls – the positive
and the negative control. What is the difference between the two of
them? The positive control is there to help us confirm that our experimental design is suitable to test the change we want to observe That means that for the positive control, we need to choose the specific parameters in the system that will allow us to see exactly the change that we are trying to see in our experiment. And those specific parameters we will look for in the literature. With the negative control, we are trying to
see what will happen with the dependent variable if we don’t change anything to the system. Negative control can tell us if the experimental
setup that we have made is somehow influencing our experiment. And finaly, if we are doing biological research, we have
to pay attention to the contamination that might be coming from the environment, from anything that is outside of our experimental system. This may be biological contamination from the other organisms, but it can also be any parameter from the environment that might be somehow influencing the outcome of our experiments.

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