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Today’s session

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- Pair up. One of you toss a coin 10 times. The other record on a small piece of paper how many times it comes up ‘heads’. When you have recorded 10 results, give the paper to me. Repeat until I ask you to stop.

- Unlike much of what you are used to in the physical sciences, judgements in psychology are often based on probability

- When you toss a coin, what is the probability it will come up ‘heads’?
- If you have thrown nine heads in a row, what happens to the probability that your next toss will be ‘heads’?

- If we plot the results from your earlier coin tosses on the graph below, what shape will we get?

5 heads; 5 tails

O heads; 10 tails

10 heads; 0 tails

Likely outcomes

Unlikely outcomes

5 heads; 5 tails

O heads; 10 tails

10 heads; 0 tails

- Does your partner have telekinetic powers?
- Decide who will be the researcher and who will be the participant.
- Participant will use the power of their mind to will the coin to come up ‘heads’

- If your participant’s coin came up heads, does that mean she has telekinetic powers?
- So how can we use coin tosses to test if she does?

Unlikely to be caused by chance; perhaps caused by something else

Likely to be caused by chance

5 heads; 5 tails

O heads; 10 tails

10 heads; 0 tails

- How many times out of ten must the participant’s coin come up heads before we accept that the result was not just due to chance?

- Did any participant meet or exceed the criterion?
- Does this (or would this) prove that she had telekinetic powers?
- What would we do to check?

- In psychological research we judge the importance of results by comparing them with what is likely to happen by chance.

- Everyone choose a number between 1 and 10 and write it down
- We’ll divide the class arbitrarily in half and compare the numbers they have chosen
- Do we expect that the two sets of numbers will be very different?

- The two sets of numbers will not be identical; they will be different. However:
- The difference may be due to chance
- The difference may be due to something else

- Let’s repeat the test. This time, read what’s on the card before choosing your number.

- The more consistent the difference between the two sets of numbers, the smaller the probability that the difference was caused by chance.
- However, we have to decide how unlikely a ‘chance result’ has to be before we will accept that the difference was caused by something else

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