Formulae.

Question 1

Stratified sample =

Answer 1

(Strata / total) x sample size

Question 2

Pearson capture - recapture:

Answer 2

( Num in 1st x num in 2nd ) / num in 2nd that are marked

Question 3

Angles in a pie chart =

Answer 3

(360 / total frequency) x frequency for each class

Question 4

Frequency density of histograms =

Answer 4

Frequency / class width

Question 5

Mean of discrete data =

Answer 5

Sum of all values / number of values

Question 6

Mean in a grouped frequency table =

Answer 6

Sum of (frequency x midpoint) / sum of frequencies

Question 7

Weighted mean =

Answer 7

Sum of (weight x value) / sum of weights

Question 8

Outliers =

Answer 8

Values > UQ + (1.5 x IQR)
OR
Values < LQ - (1.5 x IQR)

Question 9

Skewness by inspection :

Answer 9

Positive skew - distribution is shifted leftwards
No skew - symmetrical distribution e.g. normal distribution
Negative skew - distribution is shifted rightwards

Question 10

Seasonal variation =

Answer 10

Actual value - trend value

Question 11

Mean point on scatter diagrams =

Answer 11

(Mean of x values, mean of y values)

Question 12

Index number =

Answer 12

(Price / base year price) x 100

Question 13

Weighted index number =

Answer 13

Sum of (index number x weight) / sum of weights

Question 14

Chain base index numbers =

Answer 14

( Price / last year’s price ) x 100

Question 15

Standard population =

Answer 15

( Number in age group / total population ) x 100

Question 16

Standardised rate =

Answer 16

( Crude rate / 1000 ) x standard population

Question 17

P(event) =

Answer 17

Number of successful outcomes / total number of outcomes

Question 18

Expected frequency of event A =

Answer 18

P(A) x number of trials

Question 19

Estimated probability =

Answer 19

Number of trials with successful outcomes / total number of trials

Question 20

Risk =

Answer 20

Number of trials in which event happens / total number of trials

Question 21

Relative risk =

Answer 21

Risk for those in the group / risk for those not in the group

Question 22

Mutually exclusive events =

Answer 22

P(A or B) = P(A) + P(B)

Question 23

Mutually exclusive, exhaustive events = (2)

Answer 23

P(A) + P(not A) = 1

P(not A) = 1 - P(A)

Question 24

Probability of A or B in independent events =

Answer 24

P(A or B) = P(A) + P(B) - P(A and B)

Question 25

Probability of A and B in independent events =

Answer 25

P(A and B) = P(A) x P(B)

Question 26

Probability B given A conditional events =

Answer 26

P(B|A) = P(B and A) / P(A)

Question 27

Three formulae used to check for independency in events =

Answer 27

P(A|B) = P(A)
P(B|A) = P(B)
P(A) x P(B) = P(A and B)

Question 28

Standardised score =

Answer 28

(Score - mean) / standard deviation

Question 29

Z scores =

Answer 29

(Value - sample mean) / standard deviation

Question 30

Predicted value seasonal variation

Answer 30

Predicted value = trend line value + estimated mean seasonal variation