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Question 1

3 points for how a sample can be used - simple random

Answer 1

• allocate number (1-N) for each
• use random number tables to select (sample size number) diff numbers
• pupils corresponding to numbers become sample

Question 2

simple random sampling definition

Answer 2

every sampling unit equal chance chosen - e.g. hunger games to get tributes

Question 3

adv simple random

Answer 3

bias free
easy + cheap to implement
each number equal chance

Question 4

disadvantages simple random

Answer 4

• not suitable for large population size

- sampling frame required (e.g. choose 15 numbers)

Question 5

population defintion

Answer 5

whole set items are of interest

Question 6

define sample

Answer 6

subset population intended to represent population

Question 7

what’s a sampling unit

Answer 7

each individual thing in population that can be sampled

Question 8

what’s a sampling frame

Answer 8

sampling units individually named / numbered to form a list

DATABASE OF ALL POPULATION

Question 9

census

Answer 9

data collected from entire population

Question 10

advantage census

Answer 10

gives completely accurate result

Question 11

disadvantage census

Answer 11

• time consuming and expensive
• cannot be used when testing involves destruction (e.g. finding number biscuits in machine filled bag)
• large volume data to process

Question 12

sample advantages

Answer 12

cheaper
quicker
less data to process

Question 13

disadvantages sample

Answer 13

• data not accurate

- data not large enough to represent small sub groups

Question 14

64 girls and 56 boys explain how to take a simple random sample of 15 students (3)

Answer 14

• allocate number 1 to N for each pupil
• use random number tables to get 15 diff numbers 1 to 120
• pupils corresponding to numbers become sample

Question 15

what’s systematic sampling

Answer 15

required elements chosen at regular intervals in ordered list

Question 16

how to carry out systematic sampling

Answer 16

-take every kth element where k = pp size / Samp size starting at random item between 1 and k

Question 17

systematic 50,000 names sample 100 how to obtain sample

Answer 17

• randomly select number 00 to 499 ( 001 to 500) = starting point
• select every 500th person

Question 18

advantages systematic sampling

Answer 18

• simple + quick

- suitable for large samples

Question 19

disadvantages systematic sampling

Answer 19

• sampling frame needed

- can introduce bias is sampling frame not random

Question 20

what’s stratified sampling

Answer 20

population divided into groups (strata) + simple random sample carried out in each group
-use when sample large + population naturally divides into groups (e.g. age)

Question 21

how to carry out stratified sampling

Answer 21

• same proportion Samp size/pop size sampled each strata

e. g. 20% each group

Question 22

what’s strata

Answer 22

age group etc

Question 23

advantages stratified

Answer 23

• reflects population structure

- proportional rep of all groups within population

Question 24

disadvantages stratified

Answer 24

• population clearly classified into distinct strata

- selection in each stratum suffers same disadvantages as simple random sampling

Question 25

stratified example: 15 classes + sixth form w/ 30 in class and 150 in sixth form equal number girls and boys in classes same for sixth form 
- how to carry out stratified sample of 40 (7)

Answer 25

-total in skl = 600
-random sample 40/600 = 2 from each class
-150/600 x40 = 10 from sixth form
-labels boys 1-15 and girls 1-15 in class
-choose 1 boy 1 girl
-girls 1-75 and boys 1-75 in sixth form
-5 boys 5 girls
(CHOSEN USING RANDOM N GENERATOR)

Question 26

what’s a lottery sample in simple random sampling

Answer 26

100 (population size) names on paper - into bowl and draw sample size e.g. 12

Question 27

what are the 2 types of non random sampling

Answer 27

quota and

Question 28

what’s a quota

Answer 28

fixed share/number of something

Question 29

why would random sampling be problematic when doing survey on whether being left handed affects IQ

Answer 29

don’t have a sampling frame - list of all left handed ppl in UK

Question 30

what is quota sampling

Answer 30

population divided into groups depending on characteristic

-q

Question 31

how to carry out quota sampling (non random)

Answer 31

interviewer selects sampling units

Question 32

advantage quota sampling

Answer 32

• sample obtained quickly
• cheap
• admin of survey easy

Question 33

disadvantages quota

Answer 33

• cannot estimate sampling error
• process not random bias
• surveyor cannot identify sampling units easily e.g. species fish

Question 34

explain how to use quota on sample 30 w/ 2450 fish 1400 trout 600 bass 450 pike (4)

Answer 34

-1400/2450 x 30 = 17.14
-600/2450 x30 = 7.35
-450 / 2450 x30 = 5.51
fish caught until quota filled

Question 35

what’s opportunity sampling

Answer 35

find ppl at same time survey found out (branch of quota) - similar to exit polls at polling stations

Question 36

advtanges opportunity

Answer 36

• easy

- inexpensive

Question 37

disadvantages opportunity

Answer 37

• unlikley to represent sample

- depend on individual researcher

Question 38

at the Start of stratified sampling 3 marker say

Answer 38

label each strata

Question 39

distribution for fair 5 sided spinner w/ 1 round

Answer 39

(Discrete) uniform (distribution)

Question 40

why does large data set data need to be ‘cleaned’

Answer 40

Tr(ace) (data needs to be converted to numbers before the calculation can be carried out)