Chapter 1 Data collection Flashcards
What is a population?
Give and example and what this could mean?
A population is the whole set of items of interest.
A population could be items produced by a factory.
This is known as raw data.
What is a census?
A census observes or measures every member of the population.
What is a sample?
A selection of observations taken from a subset of the population which is used to find information about the population as a whole.
What is one advantage of a census?
- It should give a completely accurate result.
what are 4 disadvantages of censuses?
- Time consuming and expensive.
- Cannot be used when the testing destroys the item.
- Time consuming to process large quantities of data.
What is the advantages of a sample?
- Less time consuming and more expensive than a census.
- Fewer people have to respond.
- Less data to process than a census.
What are the disadvantages of a sample?
-The data may not be as accurate
- The sample may not be large enough to give information about sub groups of the population.
(sample may be too small).
What are sampling units?
The individual units in a sample.
What is a sampling frame?
A numbered list with all the individual sampling units.
What is particular about random sampling?
What does this do?
Every member of the population has an equal chance of being selected.
This helps to remove bias from a sample.
What are the 3 methods of random sampling?
1-Simple random sampling
2-Systematic sampling
3- Stratified sampling
How to simple random sampling work?
To carry out simple random sampling you need a sampling frame, a list of people or things.
Each person or thing is given a number.
And a selection of numbers is chosen at random.
Generate a number through a calculator or other random method
What are the two ways of choosing the numbers in simple random sampling.
- Method 1- Generating random numbers using a calculator or computer.
- Method 2- Lottery sampling, members of sampling frame written on tickets.
What is the particular thing about systematic sampling?
The required elements are chosen at regular intervals from the ordered list.
How is systematic sampling done on a population 200 and you needed a sampling size of 20.
200/20=10
You would take every 10th Person
You would take a random starting point between the interval eg 1-10
What is the key of stratified sampling?
The population is divided into mutually exclusive strata (Males and Females for example) and a random sample is taken from each.
What is the formula for the number of people sampled in a stratum?
Number in stratum/number in population x overall sample size.
What are the advantages of simple random sampling?
- Free of bias.
- Easy and cheap to implement for small populations.
- Each sampling unit has an equal chance of selection.
What are the disadvantages of simple random sampling?
- Not suitable when population size is large
- Sampling frame is needed.
What are the advantages of systematic sampling?
- Simple and quick to use.
- Suitable for large samples and large populations.
What are the disadvantages of systematic sampling?
- A sampling frame is needed
- Can introduce bias is sampling frame is not random.
What are the advantages of stratified sampling?
- sample represents the population better.
- Guarantees proportional. representation, of groups, within a population.
Disadvantages of stratified sampling?
- Population musty be clearly classified into distinct strata.
- Selection within each stratum has same disadvantages of simple random sampling.
What are the two types of non-random sampling?
Quota sampling and opportunity sampling.
What is particular about quota sampling?
In quota sampling an interviewer selects a sample that represents the characteristic of the whole population.
Until the quota is full.
How does quota sampling work?
What does the interviewer do?
step 1 -The population is divided into groups according to a given characteristic.
The size of each group should determine the proportion that should have that characteristic.
step 2 -Interviewer meets people assesses group and allocates into appropriate quota.
-Step 3 this continues until all quotas have been filled.
What happens if the Quota is full or someone refuses to be sampled?
They are ignored and the interviewer moves on to the next person.
What is opportunity sampling also called?
Convenience sampling.
What is particular about opportunity sampling?
Consists of taking a sample from those people who are around when you are taking the study and fit the criteria you set out.
What are the advantages of Quota sampling?
- Allows a small sample to be representative of the whole population.
- No sampling frame required
–Allows easy comparison between groups in a population.
What are the disadvantages of quota sampling?
- Introduces bias
- Population must be divided into groups which can introduce bias.
- Increasing scope of study increases number of groups, which adds time and expense.
- Non responses are not recorded.
What are the advantages of opportunity sampling?
- Easy to carry out
- Inexpensive
What are the disadvantages of opportunity sampling?
unlikely to provide representative sample.
- Highly dependent on individual researchers.
How can you do quota sampling in context?
4 steps
1-Divide the population into groups according to given characteristics.
2-The size of each group determines the proportion of the sample that should have that characteristic.
3-The interviewer should assess which group people fall into, as part of the interview.
4-Once a quota has been filled, no more people in that group are interviewed.
How could you do opportunity sampling in context?
Only sample the people who are available at the time the study is carried out, e.g. the first 40 shoppers who are available to be interviewed.
What is a discrete variable?
A discrete variable can only take specific variables.
What is a continuous variable?
A variable that can take any value in a given range.
