survey and sampling

Question 1

what are surveys?

Answer 1

a set of simple questions that give us an idea of whats happening commonly in the form of questionaires and can be online or written

it takes a subset of the population

Question 2

how do you find a random sample?

Answer 2

mean/ x and x is assumed to be 50

have to be 95% confident the mean is between 40 to 60

Question 3

method 1 of finding the random sample

Answer 3

first find your range max
take out numbers using their first few numbers of digits depending on max range and only numbers below the range can be noted
you cant include the same number twice
after his find each number corresponding to each number youve found witht in the range
add them all up and divifr by how many numbers

Question 4

method 2 of random sample

Question 5

when can you overprepresent in sampling?

Answer 5

in smaller groups there may be a slight overrepresentation

Question 6

how do you figure out how many people to select?

Answer 6

first find the percentage of the entire population for each category

once found do the percent to the sample you will use and that will give you how many should be selected for each part of the survey

Question 7

Simple Random Sampling

Answer 7

Type of Probability Sampling

Sampling units have same probability of selection
Need a sampling frame
Complete list of population

Question 8

Stratified Random Sampling

Answer 8

Population might be made up of different strata, e.g. gender, ethnicity, …

Simple random sampling may miss out or over-represent certain groups

Divide population into groups
Take simple random sample from each group

Sample frame required
Including information pertaining to each stratum

Question 9

Systematic Sampling

Answer 9

Type of probability sampling method

sample selected according to a random starting point but with a fixed interval.

Sampling interval, is calculated by dividing the population size by the desired sample size.

Choose first sampling unit at random
Subsequently select every nth sampling unit

Question 10

Systematic Sampling: Problems

Answer 10

Not a true random sample
Can lead to bias – e.g. if every nth sampling unit is similar and not representative

Question 11

example of systemic sampling

Answer 11

Example: systematic sampling from a list numbered 1 to 120
Population size is 120 and required sample size is 10
120 / 10 ≈ 12 so use an interval of 12.
Pick a reference number between 1 and 12 at random
Suppose number picked is 10
ID numbers selected will be:
10, 22, 34, 46, 58, 70, 82, 94, 106, 118.

The sample will have similar properties to a simple random sample if the list you selected from is randomly ordered.

Question 12

Possible practical problems with sampling

Answer 12

Questionnaire not completed / not returned

Question 13

Cluster Sampling

Answer 13

A cluster can be considered a representative sample which is, conveniently, located in just one place - “ready made”.
A cluster must be representative of the population in that
the “mix” of people within the cluster is similar to the mix in the population. We survey everyone in the cluster.
A good cluster will be similar to the final (overall) stratified random sample but without all the hard work!

Question 14

Examples of cluster sampling

Answer 14

Population: 1st year students Cluster: lecture group
Population: bank customers Cluster: street residents

Question 15

which sampling technques Requires the population list?

Answer 15

Cluster Sampling NO

Stratified Random Sampling YES

Quota Sampling NO

Simple Random Sampling YES

Systematic Sampling YES

Question 16

How to do Quota sampling

Answer 16

Decide which groupings of people are relevant to your survey

Suppose you decide on age and gender.

Assuming you have no list of the population, base age and gender proportions on information about the population of UK.

Calculate the quota size for each age and gender combination from these proportions and your overall sample size.

Stop passers by and interview them, if they allow this.

Vary time and location. Stop when all quotas are filled.

Question 17

Data Collection Methods

Answer 17

Postal/Online Questionnaire
Telephone Interview
Personal Visit
Street Interview

Question 18

Positivies off Postal/Online Questionnaire

Answer 18

Relatively cheap
Easy to organise

Question 19

Potential issues with postal/Online Questionnaire

Answer 19

No opportunity to clarify
Non-response bias – send reminders, offer incentives
Low response rates – as above

Question 20

Positives of telephone Interviews

Answer 20

Cheap and easy to organize (skilled interviewers can complete a lot of surveys in a day of work.)
large audience for gathering a representative sample to complete the survey.
High response rate than web-based survey
Clarify questions

Question 21

Potential issues of personal Visits

Answer 21

Interviewers need training
Expensive

Question 21

Potential issues of telephone Interviews

Answer 21

Can annoy people – arrange call time before if possible
Time consuming
Requires training for interviewers

Question 22

Positives of personal Visits

Answer 22

High response rate
Clarification of ambiguities
Good for collecting detailed information

Question 23

Positives of street Interviews

Answer 23

High response rate
Clarification of ambiguities
Often used with quota sampling

Question 24

Potential issues with street Interviews

Answer 24

Interviewers need training
Difficult to identify sampling units

Question 25

Past QMB(A) Exam Question: In a large university offering a wide variety of degree programmes, an increasing number of students have been expressing concerns about coping with the maths content of their courses. The university’s learning support centre has designed a questionnaire to gather data on whether students are aware of existing facilities for help with maths and what the opinions are of those students who have used the facilities. The learning support centre only has sufficient resources to study a sample of 400 students.

a) Define relevant Population

b) Describe appropriate sampling method: pay attention to feasibility and potential issues

c) Select and justify most effective data collection method

Answer 25

a) All the students at Loughborough University whose degree has some maths content and who therefore might need to use the maths support centre.

b) Since LU will have a list of all its students and information on their degree programme, we can use a random sample selection method thus avoiding selection bias. We have the information we need to use stratified random sampling. To stratify, we can check the number of students on each degree programme with some maths content and then calculate the proportion in the population we have defined. We can then use the same proportions for the sample of 400 students. This will ensure that no degree programme is either over or under represented in our sample.

A problem with stratified random sampling is that not all students that are selected and asked to complete the questionnaire will respond. This will introduce non-response bias (for example students with “neutral” opinions or students from some degrees could be under represented). To encourage a good response rate, we can provide an incentive and send reminders to non-responders. Alternatively, we could use quota sampling but, because this is a non-random selection method ,we may get selection bias (students with no strong feelings about the maths centre may not want to take part in the survey).

c) We have the email addresses of all students at Loughborough university, hence we can send online questionnaires to the selected students. This is a cheap and effective approach as all students will be checking their email regularly, and is not more costly to send reminders.

Question 26

Questionnaire Design

Answer 26

Must be clear about purpose of study before designing questionnaire
Otherwise, how do you know what to ask?

What do you need to know?

What question(s) do you need to get this information?

Question 27

Designing an opinion survey: decisions

Answer 27

Aims: information needed is opinions about……..?

Given these aims, relevant population to survey is…..?

Survey the whole population or select a sample?

Best way to select a representative sample is……?

How can we best measure opinions about……?

Question 28

Aspects of good questionnaire design

Answer 28

A good questionnaire will:

ask the right questions

be clear and unambiguous (but not offend)

be easy to complete

be readily transferred to a computer

To achieve this consider:

Content: what do I need to ask questions about?

Language: Simple? Brief? Clear? Respectful?

Structure: What will be a logical sequence of questions?

Response format: Appropriate for question? Clear?

Layout: Looks easy to follow and complete?