Chapter 1: Data Collection Flashcards
What is a population?
A population is the whole set of items that are of interest.
What is the purpose of a census?
A census observed or measures every member of a population.
What is a sample?
A sample is a selection of observations taken from a subset of the population which is used to find out information about the population as a whole.
What are the advantages of a census?
It should give a completely accurate result.
What are the disadvantages of a census?
A census is time consuming and expensive, cannot be used when the testing process destroys the item; and produces a large quantity of data.
What are the advantages of a sample?
A sample is less time consuming and expensive than a census, fewer people have to respond, and there is less data to process.
What are the disadvantages of a sample?
In a sample, the data may not be as accurate. Also, the sample may not be large enough to give information about small sub-groups of the population.
How does sample size correlate to variation in a population?
If a population is very varied, you need a larges sample than if the population were uniform.
What are sampling units?
Individual units of a population are known as sampling units.
What is a sampling frame?
Sampling units of a population are often individually named or numbered to form a list called a sampling frame.
What are the three methods of random sampling?
Simple random sampling, systematic sampling, and stratified sampling.
What is a simple random sample?
A simple random sample of size n is one where every sample of size n has an equal chance of being selected.
How is a simple random sample carried out?
First, you need a sampling frame. Each person or thing is allocated a unique number and a selection of these numbers is chosen at random by generating random numbers or lottery sampling.
What is systematic sampling?
In systematic sampling, the required elements are chosen at regular intervals from an ordered list. The first person in a systematic sample is chosen at random.
What is stratified sampling?
In stratified sampling, the population is divided into mutually exclusive strata and a random sample is taken from each. The proportion of each strata sampled should be the same.
How can the number of people sampled in a stratum be determined?
[(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/samples
- Each sampling unit has a known and equal chance of selection
What are the disadvantages of simple random sampling?
- Not suitable for large population or sample size
- A sampling frame is needed
What are the advantages of systematic sampling?
- Simple and quick to use
- Suitable for large samples/populations
What are the disadvantages of systematic sampling?
- A sampling frame is needed
- It can introduce bias if the sampling frame is not random
What are the advantages of stratified sampling?
- Sampling accurately reflects the population structure
- Guarantees proportional representation of groups within a population.
What are the disadvantages of stratified sampling?
- Populations must be clearly classified into distinct strata
- Selection within each stratum suffered from the same disadvantages as simple random sampling
What are the types of non-random sampling?
Quota sampling and opportunity sampling.
What is quota sampling?
In quota sampling, an interviewer or researcher selects a sample that reflects the characteristics of the whole population.
How is quota sampling carried out?
The population is divided into groups according to a given characteristic. The size of each group determines the proportion of the sample that should have that characteristic.
As an interviewer, you would meet people, assess their group and then, after interview, allocate them into the appropriate quota.
This continues until all quotas have been filled. If a person refuses to be interviewed or the quota into which they fit is full, then you simply ignore them and move on to the next person.
What is opportunity sampling?
Opportunity sampling consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for.
What are the advantages of quota sampling?
- Allows a small sample to still be representative of the population
- No sampling frame required
- Quick, easy and inexpensive
- Allows for easy comparison between different groups within a population
What are the disadvantages of quota sampling?
- Non-random sampling can introduce bias
- Population must be divided into groups, which can be costly or inaccurate
- Increasing scope of study increases number of groups, which adds time and expense
- Non-responses are not recorded as such
What are the advantages of opportunity sampling?
- Easy to carry out
- Inexpensive
What are the disadvantages of opportunity sampling?
- Unlikely to provide a representative sample
- Highly dependent on individual researcher
What is a continuous variable?
A variable that can take any value in a given range.
What is a discrete variable?
A variable that can take only specific values in a given range.
Give, from South to North, the five UK weather stations in the large data set.
Camborne, Hurn, Heathrow, Leeming and Leuchars
Which overseas stations are in which hemisphere?
Perth is in the southern hemisphere. Beijing and Jacksonville is in the northern hemisphere.
