1
Q
What is a population ?
A
- the entire set of items (sampling units) in the group being studied
2
Q
What is a sample ?
A
- a subset of the population where observations are taken form to represent the whole population
3
Q
What are sampling units ?
A
- each individual thing in the population that can be sampled
4
Q
What is a sampling frame ?
A
- a list of the individually named or numbered sampling units
5
Q
What is a census ?
A
- when data is collected from the entire population
6
Q
What are the advantages of a census ?
A
- they give a completely accurate result as they look at every member of the population
7
Q
What are the disadvantages of a census ?
A
- time - consuming
- expensive
- cannot be used of the testing process involve destroying the item ( because then everything will be destroyed )
- hard to process a large volume of data
8
Q
What are the advantages of a sample ?
A
- less time- consuming
- less expensive
- quicker as fewer people have to respond
- less data to process that in a census
9
Q
What are the disadvantages of a sample ?
A
- data may not be accurate
- data may not be large enough to give information about small sub groups in the population
10
Q
What is random sampling and what are the three types ?
A
- when every member of the population has an equal chance of bing selected, it helps to remove bias
- 3 types :
- simple random sampling
- systematic sampling
- stratified sampling
11
Q
What is simple random sampling ?
A
- when ever sampling unit in the sampling frame has an equal chance of being chosen
12
Q
How do you carry out simple random sampling ?
A
- use sampling frame where each sampling unit has a unique identifying number
- the use a random number generator or use lottery sampling ( when its pulled out of a hat )
13
Q
What are the advantages of simple random sampling ?
A
- bias free
- easy and cheap to implement ( on small samples and populations )
- each sampling unit as a known and equal chance of being chosen
14
Q
What are the disadvantages of simple random sampling ?
A
- not suitable when the population size is too large , then it will be time consuming, disruptive and expensive
- needs a sampling frame
15
Q
What is systematic sampling ?
A
- when the required units are chosen at regular intervals in an ordered list
- taking ever kth element where
- k = population size (N) / sample size (n)
- then starting at a random number between 1 and k.
16
Q
What are the advantages of systematic sampling ?
A
- simple and quick to use
- suitable for large samples/populations
17
Q
What are the disadvantages of systematic sampling ?
A
- needs a sampling frame
- can lead to bias if the sampling frame is not random
- so the sampling frame should be in a random order
18
Q
What is stratified sampling ?
A
- the population is divided into strata ( groups ) based on characteristics and then a simple random sampling is done to each group
- using the same proportion as the overall sample number to sample from each strata
- to work how many sampling units to take from each strata: sample size / population size ( of strata )
If its a percentage, work out percentage of that strata population - e.g if in a population there 20 blue items and we want a sample of 20% of the population then we would do 20 % of 20 to get 4 blue items in our sample
- or if you want 20% of the population, work out 20% of the total population of 50 which is 10
- then do 10/50 times each strata to get how many your should pick from each strata
19
Q
What are the advantages of stratified sampling ?
A
- sample will accurately reflect population structure
- guarantees proportional representation of groups in the population
20
Q
What are the disadvantages of stratified sampling ?
A
- population has to be clearly classified into distinct strata
- same disadvantages of simple random sampling when it is done to each strata
21
Q
What is non-random sampling ?
A
- when each sampling unit does not have an equal chance of being chosen
- usually has no sampling frame
22
Q
What are the two types of non-random sampling ?
A
- quota and opportunity sampling
23
Q
What is quota sampling
A
- when the population is divided into groups based on a characteristic of interest
- then determine the size of each group in the sample so it reflects the population ( like in stratified sampling )
- then an interviewer would choose people to be in each quota ( group ) by assessing which group they are in and then allocating them to the right quota
- once the quota is full, they stop
- if a person refuses to be interviewed , they are ignored and you move onto the next person
24
Q
What are the advantages of quota sampling
A
- allows a small sample to still be representative of the whole population
- doesn’t need a sampling frame
- quick, easy and cheap
- allows for easy comparison between different groups in the population
25
What are the disadvantages of quota sampling ?
- as its non-random, it can introduce bias as a certain type of person will answer to an advert
- having to divide the population into groups can be expensive and inaccurate
- to increase the scope of the study, more groups have to be added = more expensive and more time consuming
- non-responses are not recorded
26
What is opportunity sampling
- when the sample is taken from people who are available at the time, if they meet the criteria because the survey happens at the same time
- interviewer selects the actual sampling units according to the set criteria
27
What are the advantages of opportunity sampling ?
- easy to carry out
- cheap
28
What are the disadvantages of opportunity sampling ?
- sample in probably not representative
- highly dependent on individual researcher
29
What are the 4 types of data ?
- qualitative and quantitate
- which can either be discrete of continuous
30
What is qualitative and quantitative data ?
- qualitative = non numerical
- quantitative = numerical
31
What is discrete data and continuous data ?
- discrete = can only take specific values = shoe size
- continuous = can take any decimal value = the mass of a person
statistics year 1- a-level maths
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