S&M - Data Collection

Question 1

what is a population?

Answer 1

a whole set of items that are in interest

Question 2

what does a census observe or measure?

Answer 2

it observes or measures every member of a population

Question 3

what is a sample

Answer 3

a selection of observations taken from a subset of the population who’s is used to find out information about the population as a whole

Question 4

advantages of census

Answer 4

it should give a completely accurate result

Question 5

disadvantages of census

Answer 5

-time consuming & expensive
-cannot be used when the testing process destroys the item
-hard to process large quantity of data

Question 6

advantages of sample

Answer 6

-less time consuming & expensive than a census
-fewer people have to respond
-less data to process than in a census

Question 7

disadvantages of sample

Answer 7

-the data may not be as accurate
-the sample may not be large enough to give information about small sub-groups of the population

Question 8

why can the size of the sample affect the validity of any conclusions drawn?

Answer 8

-the size of the sample depends on the required accuracy and available resources
-generally, the larger the sample, the more accurate it is, but you will need greater resources
-if the population is very varied, you need a larger sample than if the population were uniform
-different samples can lead to different conclusions due to the natural variation in a population

Question 9

what are sampling units?

Answer 9

individual units of a population

Question 10

what’s a sampling frame?

Answer 10

sampling units of a population individually named or numbered

Question 11

a supermarket wants to test a delivery of avocados for ripeness by cutting them in half.

1) suggest why they shouldn’t cut them all in half

2) suggest one way they could improve their estimate

Answer 11

1) testing all would mean none left to sell, a census is not appropriate (when testing a product destroys it)

2) they could take a larger sample, this would give better estimate of overall proportion of ripe avocados (larger samples produce more accurate predictions about a population)

Question 12

random sampling

Answer 12

-every member of population has equal chance of being selected
-sample therefore should be representative of the population
-it also helps to remove bias from a sample

Question 13

what are the 3 methods of random sampling?

Answer 13

-simple random sampling
-systematic sampling
-stratified sampling

Question 14

how to carry out simple random sampling?

Answer 14

-you need a sampling frame
-each person / thing is allocated a unique number and a selection of these numbers is chosen at random
-there are 2 methods of choosing numbers: generating random numbers & lottery sampling
-in lottery sampling, members of sampling frame could be written on tickets and placed into a hat

Question 15

how to carry out systematic sampling

Answer 15

the required elements are chosen at regular intervals from an ordered list

use random number generator to select first one you are going to start at

eg if a sample size of 20 was required from a population of 100 you would take every fifth person since 100/20 = 5

Question 16

how to carry out stratified sampling?

Answer 16

the population is divided into mutually exclusive strata (males and females for examples) and a random sample is taken from each

Question 17

how to calculate number of sampled in a stratum?

Answer 17

number in stratum / number in population x overall sample size

Question 18

advantages of systematic sampling

Answer 18

-simple and quick to use
-suitable for large samples & populations

Question 19

disadvantages of systematic sampling?

Answer 19

-a sampling frame is needed
-it can introduce bias if the sampling frame is not random

Question 20

advantages of stratefied sampling?

Answer 20

-sample accurately reflects the population structure
-guarantees proportional representation of groups within a population

Question 21

disadvantages of stratefied sampling?

Answer 21

-population must be clearly classified into distinct strata
-selection within each stratum suffers from the same disadvantages as simple random sampling

Question 22

what are the 2 types of non-random sampling?

Answer 22

-quota
-opportunity

Question 23

process of quota sampling?

Answer 23

-an interviewer or researcher selects sample that reflects characteristics of whole population
-divided into groups according to characteristic
-allocate groups into appropriate quota

Question 24

process of opportunity sampling?

Answer 24

-take sample from people who are available at the time the study is carried out and who fit the criteria you are looking for
-eg first 20 people you meet outside a supermarket

Question 25

advantages for quota sampling?

Answer 25

-allows small samples to still be representative of population -no sampling frame -quick, easy, inexpensive -allows for easy comparison between different groups within a population

Question 26

disadvantages for quota sampling?

Answer 26

-non-random sampling can introduce bias -population must be divided into groups which can be innacurate/costly -increasing scope of study increases number of groups which adds time/expense -non-responses are not recorded as such

Question 27

advantages of opportunity sampling?

Answer 27

-easy to carry out -inexpensive

Question 28

disadvantages of opportunity sampling?

Answer 28

-unlikely to provide representative sample -highly dependent on individual researcher

Question 29

quantitative data

Answer 29

variables / data associated with numerical observations

Question 30

qualitative dara

Answer 30

variables / data not associated with numerical observations

Question 31

continuous variable

Answer 31

a variable that can take any value in a given range

Question 32

discrete variable

Answer 32

a variable that can take only specific values in a given range

Question 33

why might a binomial distribution be suitable?

Answer 33

-fixed number -the probability is constant -there are 2 outcomes