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Variables & fair testing; teaching the heart of science experiments

Written by Ben Newsome on April 19th, 2016.      0 comments

Variable testing
Teaching variable testing to students

Whilst this is not the most 'fun' science article to cover, it cover one of the most important aspects of science teaching that needs to be addressed if you're going to ensure that your class understands exactly how the scientific method actually works. Whether you're teaching science to primary kids, secondary students, preschoolers or undergraduate students, your ability to convey the importance and the skill of fairly testing variables is critical for learners taking their first steps into the scientific world. We've been teaching the scientific method in a science incursions for several years in schools, and during these visits we've often found that people request a simple overview of how teachers can teach scientific methodology in their own classrooms regardless of what the scenario actually is.

Kids using pipettes to run an experiment

In plain language, most of the scientific method simply boils down to a researchers ability to identify a question that they want to ask, where they can use controls to modify just one aspect of a given situation so that measurements can be taken and a valid conclusion can be drawn. This typically involves a step by step process, again in plain language:

  1. Identify what are the things going on in a given situation (temperature, humidity, light levels, plant height etc). We'll call these conditions from now on.
  2. Determine if any of the conditions above can be changed at all. From now on, we'll call changing 'varying'.
  3. If one of the conditions can be varied, can you accurately measure this condition (eg. temperature)?
  4. Determine if the rest of the conditions can be controlled (eg. put everything in a greenhouse?). If so, proceed further. If not, do you think it matters or to put on another way - would your results be open to someone saying that your experiment was done poorly as there was something else affecting your experiment that you should have taken account of?
  5. Knowing that you can accurately modify a condition and measure it while you control everything else, is there anything about the situation where you would like to find out about? What I mean by this is, can you create an experiment where you can change a measurable condition to see if it has any effect on another measurable condition of the experiment (eg. does plant height get affected by temperature)?
  6. Make a prediction based on your prior knowledge on how you think varying this condition will affect the other condition (eg. perhaps you might think that plant height increases as you increase the temperature).
  7. Run the experiment, whereby one situation's conditions never change at all (eg. plant stays at the same temperature for 2 weeks) and at the same time run another situation where one of the conditions is changed over the same given time frame and you measure the affects (eg, the plant height is measured on a regular basis each time you increase temperature in one experiment and don't do so in another experiment).
  8. Record the results accurately each time you do the experiment. Hopefully you replicate your study lots of times to get rid of any mistakes you might have made.
  9. Draw a conclusion based on your results
  10. Write up the experiment so that someone else can reproduce what you did using your instructions and see if they also produce the same result.
Now after explaining the above to your students and letting them get used to the idea, you can start to introduce scientific language. Change the word "condition" to "variable" for a start and highlight that the word variable comes from the word "vary" i.e. to change. This pretty much indicates what we're trying to do in lots of ways! So, once the student come to grips that you have variables in an experiment it is time to introduce the types of variables without confusing them. Personally I've found it easier to ask the following:
  • what did we vary each time in the experiment?
  • what did we measure in hope of seeing a different result after varying the experiment?
  • what other things did we control in our experiment?
In the above example, the students will quickly identify that you were changing the temperature each time and that we were hoping to see a change in the plant height, with everything else remaining constant in the greenhouse. Now it's time to put a list up on the board of the above questions except this time we give them their scientific names:
  • The independent variable is the one we varied each time in the experiment.
  • The dependent variable was the one which we measured in hope of seeing a result change in response to changing the independent variable.
  • The controlled variables were the other variables we controlled during the experiment.
Just a slight repetition and now the students can see where you're coming from. You're almost there! Ask the students to find out if they are happy with how the experiment went. They'll of course say yes/no/maybe/not sure but you can re-phrase by asking directly "Was the experiment fair or not?". Kids have an inherent idea of what is fair or not, you just have to watch them argue in the playground over taking turns! All you have to do is have them evaluate the experiment and work out whether the way you ran the experiment allowed you to fairly test the question you raised, i.e. 'Does temperature affect plant growth?'. In this you can ask them a variety of questions:
  • Did we accurately measure the temperature? Was there anything that could lead to an error here?
  • Did we accurately measure the plant height? Was there anything that could lead to an error here too?
  • Did we accurately control the other variables? Was there anything that could lead to an error here?
  • Was there anything else in the experiment replications that gave a result that could be considered unfair? 
This is a good time now to discuss why you had the students run the experiment several times. Why? To get an average reading across the experiments to reduce experimental error. At this point, you've more or less nailed it! By having students follow the sequence of identifying and controlling variables and accurately measuring the result, all whilst posing questions as to whether the experiment is fair or not you'll go a long way to setting up the mindset needed to run any experiment in any discipline. What you're actually teaching is experimental design, a critical thinking process that should never be skipped prior to running an experiment in the real world. A great scenario to pose to students about the values of good experimental design is this: imagine if you spent 3 years and thousands of dollars on a particular study only to find out at the end that your experiment was flawed from the beginning. You'd be more than upset!

Finally, you need to mention that the point of writing up the experiment is so that someone else can repeat the way you ran it and check if they get the same results. In scientific speak, you're creating a falsifiable and repeatable experiment. In other words, are you just making stuff up or can someone test the validity of your claims? This reminds me of a very famous quote!

"No amount of experimentation can ever prove me right; a single experiment can prove me wrong." Albert Einstein

Of course, now is the time to reinforce the concept by posing an entirely new experiment and guiding them through identifying the variable types, fair testing and finally evaluating what they did. If you repeat this exercise enough times, the thought processes of a researcher will be ingrained in your students and the whole process of how scientists work will be less of a mystery. They'll then be able to identify variables quickly in any given experiment and pose a testable question that produces a valid result that can be repeated by someone else. It's definitely worth chatting with students about how they could apply the scientific process to their own lives; 
  • What is the best ratio of ingredients to use in a chocolate cake?
  • Which shampoo gives my hair most strength?
  • Which lawn fertilizer is the best to use?
  • Which octane level produces the best fuel economy in a car?
For the vast majority of situations you're looking at, there's often a way of scientifically checking what is actually going on. Essentially, the scientific method is saying ' if I have situation of X, Y,  Z... what would happen to Z if I vary X and control Y...and how can I fairly test this to record a valid answer that is reproducible and testable by someone else?'

If you follow all of this and begin to apply it in your classroom, the kids minds can only grow as result. It was the very advent of the scientific method that really accelerated civilization to produce our current way of life. Understanding how scientists work is a very important task for all teachers to instil in our students regardless if they're academically gifted or not. Unfortunately not doing so risks creating a generation with a lack of understanding of scientific processes that can quickly bring about public mistrust and even animosity against the very people using working hard to use 
verifiable evidence to improve our lives. Besides which, wouldn't be just great to have the skills to work out why things happen all the time? Sounds like a plan to me!

Happy teaching,


Ben Newsome
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