Sampling

Question 1

Simple random sampling description

Answer 1

Assign a number to each member of sampling frame and generate random number

Question 2

Simple random sampling pro

Answer 2

Representative

Question 3

Simple random sampling Con

Answer 3

Time consuming, impractical, may not get minority subsets

Question 4

Systemic sampling description

Answer 4

Chose your sample by picking every nth number of the sampling frame

Question 5

Systemic sampling Pro

Answer 5

Fast, should be representative if order is random enough

Question 6

Systemic sampling Con

Answer 6

Risk you will choose an unrepresentative sample eg. Cyclic patterns

Question 7

Stratified sampling description

Answer 7

If population clearly divides into different categories and will affect variable being measured. Need enough
Measurements from each category

Question 8

Stratified sampling Con

Answer 8

How subgroups are chosen would affect outcome

Question 9

Cluster sampling Description

Answer 9

Populations clearly divides into different groups but no reason to suppose variables wil be significantly differently distributed . Chose one or more of the clusters and sample only from those

Question 10

Cluster sampling Pro

Answer 10

Representative if sampling within clusters is good,fast

Question 11

Cluster sampling Con

Answer 11

Could be unkownn differences in subgroups

Question 12

quota sampling description

Answer 12

population is divided into different categories but you dont care aboutt the proportions. decide how many of eshc categories you are going to measure

Question 13

quota sampling pro

Answer 13

easy to do and can collect response from a large range of group

Question 14

quota sampling con

Answer 14

quotas chosen could cause bias

Question 15

tan(2a)

Answer 15

(2tan^2(a))/(1-tan^2(a))

Question 16

why might change in sign method for finding root not work

Answer 16

1) there is a repeated root
2) there is a discontinuity, change in sign but no root. Eg TanX, 1/X
3) 2 roots squeezed between consecutive integers

Question 17

why might Newton-Raphson method fail

Answer 17

1) when a starting value leads to f’(x)=0 ( a stationary point). The sequence becomes undefined
2) The sequence converges but not to the root near the starting value
3) 3 roots between 2 consecutive integers, the middle one cannot be found

Question 18

conditions for binomial distribution

Answer 18

1 conduction trials on random samples of certain sizes(n)
2 On each trial the outcomes can be classified as either success (p) or failure (q)
3 The outcomes of each trial is independent of the outcomes of any other trial
4 The probability of success p is the same on each trial