3. Introduction to Sampling

Question 1

What is sampling?

Answer 1

-A microcosm of the population

Question 2

What should sampling be? and name some main characteristics of it

Answer 2

• Representative of the population - for validity
• values are statistics or estimates (because it can’t represent everyone)
• cannot always perfectly reflect the population - there will always be some degree of distortion
• can be stratified when certain characteristics are known about a larger group (eg. age, sex).

Question 3

define population

Answer 3

a group of people or objects which are similar in one or more ways and can form the subject of study in a particular survey

Question 4

define census

Answer 4

an examination of the WHOLE population

Question 5

define sample

Answer 5

The number of units drawn from the population & examined in detail. This information is considered to apply to the whole/ rest of) the population.

Question 6

What is an elementary sampling unit?

Answer 6

a single element to be sampled in a population e.g. one age group or one particular type of retail outlet e.g. toy shops

Question 7

What is a parameter?

Answer 7

the mean, mode or median - (e.g. the average cat owner has 3 cats) calculated in the total population.

Question 8

What is a sampling error?

Answer 8

the difference between a sample estimate and the value of the population parameter obtained by complete count

Question 9

How do you calculate mean?

Answer 9

add up all the numbers and divide it by unit amount number there are - its the average

Question 10

What is median?

Answer 10

the middle number ranked in a sequence e.g. 1-9 it would be 5

Question 11

what is mode?

Answer 11

The most frequently occurring number

Question 12

What are sampling frames?

Answer 12

a list of the items or people forming a population from which a sample is taken

Question 13

What forms of sampling frames are there?

Answer 13

-Lists (yellow pages)
-Indexes
-Maps; door to door sales
Other:
-1. Electoral Register
-2. postcode address file

You can get a list for cat owner from a vet or a magazine.

Question 14

What are the 5 criteria used to evaluate sample frames?

Answer 14

1. Adequacy - does this cover everyone you want? want info of over 65s so you go for pension, however, not everyone will take a pension. Pensions are not adequate.
2. Completeness - do we have everyone in there?
3. Non-duplication - same contacts saved 3 times
4. Accuracy - Will information be accurate if a year has gone by for example.
5. convinience - How easy available is it to get?

Question 15

Sampling frame evaluation

Answer 15

• no sampling frame will fulfil all evaluation criteria requirements
• existing frames should be assessed for suitability
• sometimes it’s necessary to build sampling frames which can be time-consuming & costly
• easy to obtain in developed countries and not so easy in developing countries