Spread

Question 1

Calculate range

Answer 1

The difference between top and bottom scores

Question 2

Calculate interquartile range

Answer 2

Position of lower quartile = (n+1)/4. Count same number from end, and subtract the two numbers in these spaces

Question 3

Positives and negatives of range

Answer 3

\+ very easy to calculate 
\+ gives range in which all scores occurred 
\+ ratio, interval and ordinal data
- based only on 2 scores
- very sensitive to extreme scores

Question 4

Calculate standard deviation

Answer 4

E(x-xbar)2/n-1 all squared

Question 5

Positives and negatives of standard deviation

Answer 5

+ Best way to repost spread, as let’s you use z-scores etc
+ tells us how often values are likely to appear
+ z scores let us see what percentage of scores are above or below a certain points on a graph
- can only be used with ratio and interval data

Question 6

What does the standard deviation show?

Answer 6

Shows how scores vary around the mean. The smaller the S.D, the more bunched the scores

Question 7

How do you calculate variance?

Answer 7

1) Put scores in order. Put another row beneath and wrote how many sds from the mean they are.
2) square each deviation
3) sum all squared deviations and divide the sum by n-1

Question 8

Positives and negatives of variance

Answer 8

+ powerful measure of spread which takes all data into account

• not in the same scale/units as data as its squared
• only used with ratio and interval data

Question 9

Positives and negatives of interquartile range

Answer 9

+ indicates central group in of scores
+ can be used for interval, ratio and ordinal data

• takes no account of extreme scores