Physics
Chem
Engineering
Biology
Criticising an experiment
Author
Magnus Johansson; Bromangymnasiet Hudiksvall
Target Group
Upper secondary
Brief Description
Learning how to evaluate an experiment by providing an easily criticized experiment

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Learning to criticize a method or experiment

Students often have problems when criticizing methods – they do not focus on relevant aspects or straight out have no clue of where to begin. This lesson provides a simple plan to get students started in learning how to criticize a method or experiment. I have used this lesson with students from natural science programs as well as with students from vocational programs. In essence, the idea is to provide a ridiculous survey or experiment in which the students can easily find aspects to criticize.

I usually have this lesson after a set of lessons concerning the scientific method of inquiry:

I start this lesson by saying that I have made an observation in the class. This observation changes depending on the sex ration in the class. If it is an only boys or girls class I quickly survey the types of clothes they have, or if some have glasses or not, or types of hairstyles. It is not important that the ratio is 50:50 only that there is a difference. If I teach a mixed class I usually use the fact that some of the students are girls and some are boys.

I tell them that I have the idea that physical body strength is drawn from the hair. This would then give the hypothesis that students with long hair are stronger than students with short hair. I proceed by telling the students that I want to test this hypothesis with a simple experiment in class.

Using a hand-held dynamometer I then demonstrate how it’s used and then hand it over to students to use. I preferably use two different and pass them in different directions in the class. While the students then try their strength, I write the measurements from the two test groups on the board.

Usually there is a difference in mean strength (especially if I use girls vs. boys) and usually students immediately starts to shout that the test is wrong! Which is exactly the response I want!

After allowing a short time of vivid discussions, I then try to systemize the critique.

The following critique tend to arise:

• -          The dynamometers are different (e.g. not calibrated to each other)

• -          Different people used different techniques (e.g. sitting, standing or holding the dynamometers up)

• -          The question is not relevant (of course boys are on average stronger than girls!)

• -          The method is not relevant for testing the question (why should hand strength be a good measurement?)

• -          Biological issues (e.g. after eating, early morning or lack of sleep)

• -          Social issues (e.g. boys trying to impress in a public setting and girls do not)

• -          Testing order (e.g. the first students after me are not sure of what is expected and might underperform)

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Some of these are highly relevant (e.g. testing order) and some might not be (e.g. different techniques is only important if it confounded with group). The important thing is to follow up on the critique and ask the students how they want the method to change – providing that they want to keep the question and hypothesis!

The challenge for the students is to be able to continue this “flow” of criticism concerning their own or a fellow student’s work that is not as pre-arranged as this example.

I find that this exercise is a valuable lesson for the students as they receive both an introduction to method evaluation but also an additional lesson in the process of scientific inquiry.

## Related files

 Method criticism 168 KB
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