1. Identifying independent and dependent variables

2. The independent variable
This is the variable that the experimenter purposefully changes in order to see if it has an effect on behaviour.
In a lot of experiments, the independent variable is usually related to what the participants are doing.
E.g. one group of participants viewed ‘normal’ pictures whereas the others viewed ‘strange’ pictures

3. The independent variable
This sentence structure should work with most experiments you might see in the exam:
“Whether _________ or ________”
E.g. “whether participants viewed ‘normal’ pictures or ‘strange’ pictures”.
“whether it was before TV was introduced or after”.

4. The dependent variable
This is the variable that you measure
Although it isn’t purposefully changed by the experimenter, it does usually change as a result of the independent variable
E.g. because participants viewed the ‘normal’ pictures rather than the ‘strange’ pictures, they remembered more details of the pictures.
Remember, first the experimenter will change the independent variables, then they will measure the dependent variable.

5. The independent variable is the one that affects results
The dependent variable is the one being affected

6. Write down the IV and DV of each of these experiments…..

7. Students watched a cartoon either alone or with others and then rated how funny they found the cartoon to be.

8. IV = whether participants watched the cartoon alone or with others
Students watched a cartoon either alone or with others and then rated how funny they found the cartoon to be.
IV = whether participants watched the cartoon alone or with others
DV = how funny they found it

9. Workers at a company were assigned to one of two conditions:
One group completed a stress management training program;
Another group of workers did not participate in the training.
The number of sick days taken by these workers was examined for two months.

10. DV = the number of sick days taken
Workers at a company were assigned to one of two conditions:
One group completed a stress management training program;
Another group of workers did not participate in the training.
The number of sick days taken by these workers was examined for two months.
IV = whether participants completed a stress management training program or not
DV = the number of sick days taken

11. Students at a University were split into two groups and each received a different text for a philosophy course.
One group received a traditional text book.
The other received an interactive textbook on a tablet computer.
After the course, the final exam marks between the two groups of students was compared.

12. IV = whether they read a traditional or and interactive text book
Students at a University were split into two groups and each received a different text for a philosophy course.
One group received a traditional text book.
The other received an interactive textbook on a tablet computer.
After the course, the final exam marks between the two groups of students was compared.
IV = whether they read a traditional or and interactive text book
DV = scores on exam

13. The Halo Effect
A man made two videos for a dating website and showed it to two groups of girls.
One group watched a video in which the man read the script in an upbeat manner.
The other group of girls watched the same man read the same script but in a more melancholy fashion.
The girls then rated the man on how likeable he was.

14. The Halo Effect
A man made two videos for a dating website and showed it to two groups of girls.
One group watched a video in which the man read the script in an upbeat manner.
The other group of girls watched the same man read the same script but in a more melancholy fashion.
The girls then rated the man on how likeable he was.
IV = whether participants watched the upbeat video or the melancholy video
DV = likeability ratings

15. The Halo Effect
The girls who watched the upbeat video found the man to be likeable, while the girls who watched the second video found the man to be unpleasant, even though he had read the exact same script. Thus demonstrating the importance of tone in the perception of overall attractiveness and modelling the Halo Effect in action.

16. The Fun Theory
A Volkswagen initiative called The Fun Theory is setting out to prove that people’s behaviour can be changed for the better by making mundane activities fun.
In a recent experiment, they set up musical piano steps on the staircase of a Swedish subway station to see if more people would be more willing to choose the healthier option and take the stairs instead of the escalator.

17. The Fun Theory IV = whether the stairs were piano or escalator
A Volkswagen initiative called The Fun Theory is setting out to prove that people’s behaviour can be changed for the better by making mundane activities fun.
In a recent experiment, they set up musical piano steps on the staircase of a Swedish subway station to see if more people would be more willing to choose the healthier option and take the stairs instead of the escalator.
IV = whether the stairs were piano or escalator
DV = how many times the piano stairs were used and how many times the escalator was used

18. The Fun Theory

19. John Bargh wanted to see if the exposure to different genres of words affected behaviour.
One group were shown words which related to the elderly stereotype (e.g. wise, forgetful, retired) and the other group were shown random words which didn’t relate to a stereotype (e.g. thirsty, private).
Bargh then timed how long it took participants to walk down the hallway when they were leaving the experiment.

20. DV = time it took Ps to walk away from study
John Bargh wanted to see if the exposure to different genres of words affected behaviour.
One group were shown words which related to the elderly stereotype (e.g. wise, forgetful, retired) and the other group were shown random words which didn’t relate to a stereotype (e.g. thirsty, private).
Bargh then timed how long it took participants to walk down the hallway when they were leaving the experiment.
IV = whether participants viewed words related to the elderly stereotype or words not related to any stereotype
DV = time it took Ps to walk away from study

21. The participants who had been exposed to words related to the elderly stereotype walked along the corridor much slower than those who had not, consistent with the stereotype.

22. Controls

23. In an experiment, there are loads of possible factors that could affect the results. The only one we want to see is the effect of the independent variable on the dependent variable.
A control is something that is kept the same for every participant across the whole experiment so that we can be sure that nothing except the independent variable is affecting the dependent variable.

24. EXAMPLE: George wanted to see the effects of colour on memory
EXAMPLE: George wanted to see the effects of colour on memory. Participants were asked to memorise a list of words. He gave one group of participants a list of words in red font. Another group was given a list of words in black font. He then tested participants to see how many words the participants could recall.

25. George wanted to see the effects of colour on memory
George wanted to see the effects of colour on memory. Participants were asked to memorise a list of words. He gave one group of participants a list of words in red font. Another group was given a list of words in black font. He then tested participants to see how many words the participants could recall. What is the IV & DV?

26. George wanted to see the effects of colour on memory
George wanted to see the effects of colour on memory. Participants were asked to memorise a list of words. He gave one group of participants a list of words in red font. Another group was given a list of words in black font. He then tested participants to see how many words the participants could recall.
IV = whether they were given the list of words in red font or in black font.
DV = their recall score.
Do you think there would be a difference in recall if one group was tested at 8am and the other at midday? Why?

27. George wanted to see the effects of colour on memory
George wanted to see the effects of colour on memory. Participants were asked to memorise a list of words. He gave one group of participants a list of words in red font. Another group was given a list of words in black font. He then tested participants to see how many words the participants could recall.
If one group was given the list of words at 8 in the morning and the other group at midday, the first group may be so tired and groggy that they can’t memorise as much of the list, whereas the second group would be more awake so might remember more words.
This would mean that the time of day was having an effect on their recall (the DV).
In other words, the difference in recall scores might not be due to the colour of the words, but is really due to the time of day they were tested.

28. George wanted to see the effects of colour on memory
George wanted to see the effects of colour on memory. Participants were asked to memorise a list of words. He gave one group of participants a list of words in red font. Another group was given a list of words in black font. He then tested participants to see how many words the participants could recall.
SO……
A control for George’s experiment could be to make sure every participant is tested at the same time.
This removes the possibility that something other than the independent variable is affecting the dependent variable.
Why is the use of controls so important in experiments? Discuss in pairs.

29. Why is the use of controls so important in experiments?
If it’s not just the independent variable affecting the results, but a whole load of other factors, then we can’t really conclude anything. This is because we can’t prove that the independent variable definitely affected the dependent variable, which is what we set out to do in the first place.
This means we cannot be sure of a cause-and- effect relationship.

30. Why is the use of controls so important in experiments?
If George found that people who viewed the words in red font remembered more words, there could be multiple reasons for this:
The difference in recall could have been solely due to the font colour. Even though they were tested at different times of the day, it had absolutely no effect.
Results could have been solely due to the time of day that participants were tested. Font colour had absolutely no effect.
The difference in recall was due to both the font colour and the time of day.
There’s no way for George to know for sure!

31. Why is the use of controls so important in experiments?
If an experiment lacks control, it decreases the validity.
Validity: does the experiment measure what it set out to measure?
If we aimed to measure the effects of colour on memory, but it is possible that the time of day affected memory too, then we’re not measuring what we set out to measure.. We’re actually measuring the effects of colour and time of day on memory

32. Why is the use of controls so important in experiments?
If an experiment lacks control, it also decreases the reliability.
Reliability: Is every participant getting the same experience? Would you get the same results if you did the experiment again?
If participants viewed the word list at different times of the day, then they’re not getting the same experience.
If George did his experiment again and did them at different times than the first experiment (e.g. 3pm and 11pm) then he might get different results.

33. Remember…..
The only thing we want to change in the experiment is the independent variable.
The only thing we want to affect the dependent variable is the independent variable.
Everything else needs to be controlled.

34. There are loads of possible controls that you could use, and it really depends on the experiment. Some commonly used ones are:
The time of day should be the same for every participant (unless you’re purposefully trying to see the effects of different types of day on something)
The instructions given to every participant should be exactly the same
The location they do the experiment in should be exactly the same for every participant (unless you’re purposefully trying to see the effects of different environments on something)

35. George wanted to see the effects of colour on memory
George wanted to see the effects of colour on memory. Participants were asked to memorise a list of words. He gave one group of participants a list of words in red font. Another group was given a list of words in black font. He then tested participants to see how many words the participants could recall.
Apart from the time of day, what other things do you think George needs to keep the same for every participant? What factors could affect their recall?
Discuss in pairs.

36. George wanted to see the effects of colour on memory
George wanted to see the effects of colour on memory. Participants were asked to memorise a list of words. He gave one group of participants a list of words in red font. Another group was given a list of words in black font. He then tested participants to see how many words the participants could recall.
Size of the words
Font
Whether or not the experimenter is in the room when they memorise the words
The amount of time between memorising the words and having to recall them

37. Control groups
Another possible control we could use is to have a control group in an experiment.
In a control group, the independent variable is not present, all we do is measure the dependent variable.

38. Control groups - example
Natasha wants to see the effects of homework on stress levels. She asks every teacher at SDC to give half of their students homework which would take at least 3 hours, and the other half homework that would take 20 minutes. She then gave students a questionnaire which would measure their stress level.
If she wanted to include a control group, instead of splitting the students in half, she could split them three ways:
3 hours homework
20 minutes homework
No homework (control group)
As the IV is whether they get 3 hours or 20 minutes homework, Natasha has removed the presence of the IV in the control group.

39. Control groups
Using Natasha’s experiment to help you, why do you think using a control group is good?
It allows us to see what behaviour is like if we don’t manipulate anything (in other words, if we don’t have an independent variable).
A control group provides a baseline because we are able to see what their stress levels would be like normally.
We can then compare our main results with this baseline so we get an even better idea of how much the IV is affecting the DV.

40. Another example
Dr Foster wants to test the effectiveness of two new drugs which have been developed to treat depression. She gives some participants a drug called fluoxetine and others a drug called imipramine. Dr Foster measured the severity of a participant’s depression by using the Beck Depression Inventory, which is a questionnaire. She gives the questionnaire to each participant before and after they have completed a 2-week course on one of the new medications in order to see if there is an increase/decrease in symptoms.
What is the IV and DV?
IV: whether participants received fluoxetine or imipramine
DV: severity of depression on the Beck Depression Inventory

41. Another example
Dr Foster wants to test the effectiveness of two new drugs which have been developed to treat depression. She gives some participants a drug called fluoxetine and others a drug called imipramine. Dr Foster measure the severity of a participant’s depression by using the Beck Depression Inventory, which is a questionnaire. She gives the questionnaire to each participant before and after they have completed a 2-week course on one of the new medications in order to see if there is an increase/decrease in symptoms.
Give an example of a control group Dr Foster could use.
Doctor Foster could give them a placebo, which is something that looks like medication (e.g. it is a pill) but does not contain any drug at all.

42. Another example
Why will it be good for Dr Foster to use a control group?
If fluoxetine shows a decrease in the severity of depression, we could conclude that this drug is an effective treatment of depression.
However, if the participants in the control group showed the same decrease in depression, we would not be able to say that fluoxetine is an effective treatment for depression, as it is no better than giving patients no drug at all.
This could also be reversed (if the control group doesn’t show the same decrease in depression then we could say that fluoxetine is much better than not giving them the drug).