The document discusses different types of sampling methods that can be used when conducting surveys, including simple random sampling, stratified random sampling, systematic random sampling, cluster sampling, quota sampling, and convenience sampling. It also provides examples of each sampling method and discusses how to design questionnaires and collect reliable survey data.

1. Sample Surveys
Ms. Carter

2. SAMPLE Surveys
SAMPLE SURVEYS: are designed to ask questions of a small
group of people in hope to learn something about the entire population.
The POPULATION is the entire group that is being studied.
A CENSUS is a survey of the whole population.
A SAMPLE is a group that is selected from the population in order
to gather information.

3. Example:
An online poll use voluntary response samples.
Why would these samples have bias?

4. Types of Sampling
1. SIMPLE RANDOM SAMPLING;
A sample size of n is selected in such a way that every possible sample of size n from the population has
an equal chance of being selected.
2. STRATIFIED RANDOM SAMPLING;
To do this first divide the population into at least two different subgroups so that the individuals or
subjects within each subgroup share the same characteristics. Then a simple random sample is drawn from
each subgroup and combined to form the full sample.

5. 3. SYSTEMATIC RANDOM SAMPLE;
Basically there is a system to applying a random sampling.
That is say we wanted to have a sample of size 500 from a population of
10,000, we assign each member of the population with a number. Then we
divide the population by the sample size, thus 10,000÷500=20. Now we
randomly pick some number between 1 and 20 say 13! Then 13 becomes our
starting point and we select every 20th number from 13 onwards.

6. 4. CLUSTER SAMPLING;
For this the population is divided into sections or clusters. Then some of those clusters are randomly
selected and all members from those clusters are chosen.
5. QUOTA SAMPLING;
In quota sampling the selection of the sample is made by the interviewer, who has been given quotas to
fill from specified sub-groups of the population. For example, an interviewer may be told to sample 50
females between the age of 45 and 60.
There are similarities with stratified sampling, but in quota sampling the selection of the sample is non-
random. Anyone who has had the experience of trying to interview people in the street knows how
tempting it is to ask those who look most helpful, hence it is not the most representative of samples, but
extremely useful.

7. 6. CONVENIENCE SAMPLING;
Subjects are chosen in the most convenient way possible.

8. Examples: In each of the following, identify the
type of sampling used:
A marketing expert from RTE is conducting a survey
in which 500 people will be selected from each age
group of 10-19, 20-29, 30-39 and so on.

9. Solution
A STRATIFIED RANDOM SAMPLE
is used. Here the population is divided into distinct
groups and each group is sampled. As all the age
groups should contain the same number of people, the
same sample size is taken from each group. If the
groups or strata were of different sizes, our samples
would have to be reflect these proportions.

10. Test Ladies
The past pupils association of Colaiste an Phiarsaigh
would like to see whether past students would be
interested in a reunion. They have obtained a list of
all past pupils of the school. They decide to randomly
select a sample of people from the list and to use this
sample to gauge the interest in the reunion. They
randomly select a number between 1 and 20. The
person with this number is chosen and then every 20th
name from the first selection onwards.

11. • A researcher is testing a new drug. She has already
administered the drug to a large number of patients.
She now wants to select a sample of 20 from this
group. Fortunately, she has just addressed envelopes
which all she will use to send information to the
patients. She decides to put all the envelopes in a bag
and randomly select 20.
• Explain how you would carry out Systematic Random
Sampling on a sample of 1000 from a population of
20,000.

12. Reliability of Data
• When choosing a sample from a population, try to ensure:
• That the sample is large enough
• That the sample is a random selection from the population
• That everybody has an equal chance of being selected
• As high a response rate as possible
If sample data is not collected in an appropriate way, then the
data may be unreliable.

13. Collecting Data

14. Surveys
Most Surveys use a questionnaire and can be carried out by:
• Face-to-face interviews
• Telephone interviews
• Sending a questionnaire by post
• Making a questionnaire available online
• Observation
What do you think are the positives and negatives of each type of survey?

15. Survey Advantages Disadvantages
Face-to face interview Questions can be explained to the - Not random.
interviews. - Expensive to carry out.
Telephone interview - It is possible to select sample from almost Expensive in comparison to postal and
the entire adult population. online surveys.
- Questions can be explained to the
interviewee.
Postal questionnaire Inexpensive. People do not always reply to postal surveys
and those who reply may not be
representative of the whole population.
Online questionnaires - Very low cost. Not representative of the whole population.
Only those who go online and do online
- Anonymity of respondents ensures more surveys are represented.
honest answers to sensitive questions.
Observations - Low cost.
- Easy to administer.
- Not suitable for many surveys.
- Questions cannot be explained.

16. How do we design a questionnaire?
A questionnaire is a set of questions designed to obtain data from a population.
QUESTIONS SHOULD:
• Be useful and relevant to the survey you are understanding
• Use clear and simple language
• Be as brief as possible
• Begin with simple questions to encourage people to complete them
• Accommodate all possible answers
• Be clear where answers should be recorded
• Contain no leading questions
• Contain no questions which ask for a response to more than one topic

17. Homework Check!
1. What are the advantages and disadvantages of using an
online questionnaires when carrying out a survey?
2. You are asked to advise a 1st year students on designing a
questionnaire, what four points of information would you give
them?

18. Britney wants to gather information on people’s interest in sport. Here is the questionnaire she designs.
1. What is your favourite sport?
(i) Tennis
(ii) Rugby
(iii)Athletics
2.How far would you travel to see a competitive sports fixture?
(i) Less than 1 km
(ii) 5-10 km
(iii)Greater than 20 km
3. Do you participate in sport ow watch sport on TV?
(i) Yes
(ii) No
(a) What is wrong with these questions?
(b) Design better questions for Britney to use?

19. Steps in a Statistical Investigation
1. Define your Research Aims.
2. Identify the Population and Sample Size.
3. Decide how to Collect the Data.
- Carry out Pilot Survey.
4. Present the Data.
5. Analyse the Data.
6. Interpret the Results.

20. Solution
QUESTION 1
(a) The question does not allow for all possible sports. While it may not be
possible to include all types of sport, it is possible to cater for everybody if an
‘Other’ alternative is included.
1. What is your favourite type of sport?
(i) Tennis
(ii) Rugby
(iii) Athletics
(iv) Other

21. Q UESTION 2.
(a) There are gaps between 1km and 5km and also between 10km and
20km.
2. How far would you travel to see a competitive
sports fixture?
(i) Less than 1km
(ii) 1 - 10 km
(iii) Greater than 10km but less than 20km
(iv) 20 km or more

22. QUESTION 3.
(a) This question needs to be split into two questions.
3. Do you participate in sport?
(i) Yes
(ii) No
4. Do you watch sport on TV?
(i) Yes
(ii) No