Statistics

Question 1

How do you work out the IQR?

Answer 1

Q3 - Q1

Question 2

What are the equations you use to work out outliers?

Answer 2

Median + 1.5 x IQR

Median - 1.5 x IQR

Question 3

How do you work out the frequency density?

Answer 3

frequency / class width

Question 4

How do you work out Q1?

Answer 4

(n+1) / 4

Question 5

How do you work out Q3?

Answer 5

3(n+1) / 4

Question 6

How do you work out frequency?

Answer 6

f = frequency density X class width

Question 7

In regression equation y = 25.6 + 3.25x, where y = time spent and x=removing roof tiles, what does the y intercept and gradient mean?

Answer 7

y int = 25.6, can interpret as average setting up time (eg ladders) as 25.6 mins

gradient = 3.25, means in takes on average 3.25 mins to replace roof tile

Question 8

What % of the normal distribution curves’ area lies within ONE standard deviation of the mean?

Answer 8

68%
of the area lies within 1 standard deviation of the mean

Question 9

What % of the normal distribution curves’ area lies within TWO standard deviations of the mean?

Answer 9

95%
of the area lies within 2 standard deviations of the mean

Question 10

What % of the normal distribution curves’ area lies within THREE standard deviations of the mean?

Answer 10

99.7%
of the area lies within 3 standard deviations of the mean

Question 11

Someone claims arrival times of ambulances are normally distributed with mean time 11 mins and standard deviation 7 mins.
What is wrong with this claim?

Answer 11

normal distribution has 95% of its distribution within 2 standard deviations of the mean
but 11 - (2 x 7) = -3 [mean - (2 σ) ]
if mean + σ are correct, then times can’t be normally distributed because you can’t have negative arrival times