Distributions and Sign Test

Question 1

What will a normal distribution curve look like for an exam that was the right level of difficulty?

Answer 1

• a symmetrical bell shaped frequency distribution
• most of the scores are clustered close to the mid-point
• the mode,median and mean are all at the mid point

Question 2

Why is this? (in terms of task difficulty and normal distribution)

Answer 2

• if the task is the right level of challenging, this means few students will set a high score as this is difficult to achieve
• also few will get low scores as the challenge level is right

Question 3

What are negative skewed distributions and what do they show?

Answer 3

Non symmetrical frequency distribution

Question 4

Where is the mean, mode and median on negative skewed distributions?

Answer 4

• the mean skews the distribution to the left because it is affected by the lower scores. (greater range on left than right)
• the mode of the scores remains on the right

Question 5

Why is this? (in terms of task difficult and left/negative skewed = mean<median<mode)

Answer 5

• task is too easy (low level of challenge)
• majority will achieve high scores
• since test is very easy, most students will do well - get a high score + avoid low score

Question 6

What are positive skewed distributions and what do they show?

Answer 6

• non symmetrical frequency distribution
• the mean skews the distribution to the right bc it is affected by higher scores (greater range on the right than left)
• mode of the scores remains on the left

Question 7

Where is the mean,median and mode on positive skewed distributions?

Answer 7

• the mean skews the distribution to the right bc it is affected by the higher scores (greater range on right than left)
• mode of the scores remains on the left

Question 8

Why is this? (in terms of task difficult and right/positiveskewed = mean>median>mode)

Answer 8

• majority will get low scores that lead to a positive distribution
• mean is pulled to the right because it is affected by minority high score

Question 9

What is the role of inferential statistics?

Answer 9

enables a researcher to judge whether the data are:
-> significant (there is an actual difference/similarity between data)
-> not-significant (there is no actual difference/similarity between data, result occured due to chance)

Question 10

One tailed test:

Answer 10

indicated by a directional hypothesis, a specific outcome is tested (goes in one direction)

Question 11

Two tailed test:

Answer 11

Indicated by a non-directional hypothesis - a non specific outcome is being tested (go in both directions)

Question 12

What are p-values:

Answer 12

The probability that the findings have occured due to chance
It informs us if the difference between two conditions is menial enough to be a fluke or significant enough to be due to manipulation of IV. These are written as a percentage or a decimal. E.g. 5% or 0.05.

Question 13

What does it mean if p<_ 0.05

Answer 13

=5%
= Less than 5% likelihood that difference/ correlation is due to chance
= 95% likelihood due to manipulation of IV

Question 14

What is the significance level (p-value) that psychologists use?

Answer 14

-> a stricter, smaller p-value is used when there is no previous research, or the researcher needs to be confident of the result
-> a lenient, larger p value is used when the study is a replication of existing research or the researcher does not need to be confident of the result

Question 15

What does a lower p-value show?

Answer 15

More confident that difference/correlation is genuine

Question 16

What does a higher p-value show?

Answer 16

Less confident that difference/correlation is genuine

Question 17

What is a sign test:

Answer 17

A type of inferential statistic. A way of judging whether two sets of data are significantly different

Question 18

Conditions required for a sign test:

Answer 18

The sign test is used when using:
- test of difference between the conditions
- repeated measures or matched pairs design
- nominal data: data which is in catagories or which can be converted into catagories
++++ everyone of these needs to be met (and apply to q each point)

Question 19

How to do a sign test?

Answer 19

1. State the hypothesis
2. Gather and record the data
3. Work out the difference between the scores
4. Work out the sign (+ if difference is positive, - if negative. If the difference is 0 then data is omitted)
5. Work out the calculated value for S
6. Add up the pluses and minuses
7. Select the smaller value as the calculated value
8. Find the critical value of S from a critical values table
9. Report the conclusion and state which hypothesis to accept

Question 20

Writing a conclusion statement:

Answer 20

Since the calculated value of S(___) is less/more than the critical value of S(___), the difference is/is not significant for N=____ and p<_0.05