The experimental method

In my experience the most effective way of helping students understand the experimental method is through carrying out an experiment with the class. The Teacher’s Companion (handouts 137 and 138) contains resources to conduct a class memory experiment or you could run a simple stroop test as explained below. The following activities could be used to form part of a lesson introducing the experimental method.

Please note, a version of a lesson **PowerPoint** has been included should you wish to use/edit/amend it.

Starter
(Slide 1) Often students have some awareness of the following terms from GCSE or BTEC Science:
-Variables
-Experiments
-Aims
-Hypothesis
-Conditions
-Measurements
-Controls.

Working in pairs or small groups students define these terms and then feedback to the class. Correct any errors in thinking and take time to discuss any other scientific terms that are offered. At this point I find it helpful to reinforce the difference between an aim and a hypothesis (in the past I have seen a few students write hypotheses as questions which obviously is not credited in an exam).

Main activities

(Slide 2-5)
The stroop test involves a participant first reading a list of colour words (condition 1) followed by seeing a second list of colour words and stating the colour ink the word is written in (condition 2). As reading is an automatic process – we cannot help but read the word when it is presented to us – participants are usually slower in completing the second condition as they have to divert their attention from the meaning of the word to focus on ink colour.

There are two ways to run the stroop test.
1. You may wish to ask a few volunteers to play the role of participants.  Make sure participants wait outside the classroom until it is their turn so they are not exposed to the words prior to testing. Nominate someone in the class to time how long it takes each participant to read the list of words aloud (condition 1) and read the colour font aloud (condition 2). Record times for all participants and discuss the findings – which condition took longer? Why?

2. Alternatively students could be placed in pairs with one taking on the role of experimenter, the other playing the participant. Students can use the stop watch function on their mobile phone to time their participant’s performance on both conditions. This may become very noisy in a large class but offers an opportunity to discuss why this might impact on validity of the data collected.

Review

Once data has been discussed test students understanding of the experimental method using the questions (with supportive notes) shown on slide 6.
Answers.
1. It was a repeated measures design.
2. IV = Whether participants read the words or the colour the words were written in.
3. DV = the time it took (in seconds) to complete the list (read words/state colour).
4. We automatically read the words as this process is more automatic to us.

Reference: Stroop, John Ridley (1935). “Studies of interference in serial verbal reactions”. Journal of Experimental Psychology 18 (6): 643–662.

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