Variability and Dispersion

Question 1

What’s a limitation of the range?

Answer 1

Heavily influenced by outliers

Question 2

How do you measure the interquartile range?

Answer 2

Largest 25% and smallest 25% are taken away from the sample so you’re left with the middle 50%
Take away the largest score in the middle 50% away from the lowest score in the middle 50%

Question 3

How do you work out mean deviation?

Answer 3

Work out the mean set of scores
Work out how much each score in the sample differs from the mean
Deviations are all added up (ignore the negative numbers)
Divide by the numbers of scores

Question 4

How do you work out variance?

Answer 4

Work out the mean set of scores
Work out how much each score in the sample differs from the mean
Deviations are squared (even the negative values)
Deviations are all added up
Divide by the numbers of scores

Question 5

What is the computational formula for variance, what do the symbols mean?

Answer 5

X= each member of a set of scores
N= number of scores
∑= summation
∑X squared= the sum of the square
( ∑X) squared= sum of all the scores and squares

Question 6

How do you interpret variance?

Answer 6

Larger data sets mean larger variance
Smaller data sets means smaller variance

Question 7

What is variance estimate?

Answer 7

Best guess at what the variance of a population of scores are, IF you only have a small set of scores from that population

Question 8

What is standard deviation?

Answer 8

the square root of variance

Question 9

What is variance?

Answer 9

the average of squared differences between scores from the mean

Question 10

How do you work out the range?

Answer 10

Highest value minus the lowest value

Question 11

Why are interquartile ranges useful?

Answer 11

They aren’t influenced by outliers

Question 12

How do you interpret standard deviation?

Answer 12

small standard deviation= closer to mean
bigger standard deviation= scores are further away from the mean

Question 13

What is a standard normal distribution?

Answer 13

Mean of 0
Standard deviation of 1
See the extreme values in our data set
Compare data in different units
68% data lies within 1 SD
95% data lies within 2 SDs
99.7% data lies within 3 SDs
Frequency curve of z scores to show if there is a bell curve or a positive or negative distribution

Question 14

How can you convert to a normal standard distribution?

Answer 14

Convert to Z score
Z score: subtract mean from every value, divide by standard
How many SDs away from the mean an individual datapoint is