Statistics - Year 1

What are the advantages of simple random sampling?

• Bias free

• Easy and cheap to do

• Each number has a known equal chance of being selected

What are the disadvantages of simple random sampling?

• Not suitable when the population size is large

• Sampling frame is needed

What are the advantages of systematic sampling?

• Simple and easy to use

• Suitable for large sample sizes/populations

What are the disadvantages of systematic sampling?

• Sampling frame is needed

• Can introduce bias if sampling frame is not random

How do you carry out a simple random sample?

from your sample or population number all of the sampling units and then use a random number generator, selecting the numbers corresponding with that sampling unit.

How do you carry out a systematic sample?

Number the units in a population/sample giving you a sampling frame. Do your population size divided by sample size to give k then use a random number generator to select a number between 1 and k as a starting point. Then from that point select every k-th unit until the desired sample size is reached.

What is a very important thing to do with systematic sampling?

You have to have a random starting point, this is the only moment you might need a random number generator.

What are the advantages of stratified sampling?

• Reflects the population structure

• Guarantees a proportional representation of groups within the population structure

What are the disadvantages of stratified sampling?

• Population must be clearly stratified into distinct strata

• Selection within each stratum suffers from same problems as simple random sample.

How to carry out a stratified sample?

Identity the strata e.g. boys and girls. Then do the sample size divided by the population size. Use this value and multiply it against the sample size for each strata to determine the number of sampling units needed from each group. Then carry out a simple random sample in each group until you get to the required number.

What are the advantages of quota sampling?

• Allows small sample to still be representative of a population

• no sampling frame is needed

• Quick, easy and inexpensive

• Allows for easy comparison between different groups in a population

What are the disadvantages of quota sampling?

• Non-random sampling can introduce bias

• Population must be in groups, costly/inaccurate

• Increasing scope of study, increases groups - time/expense

• Non-responses aren’t recorded

How to carry out a quota sample?

Starts off the same as a stratified sample but instead of random sampling in each group the interviewer selects the actual sampling units to fill the quota.

Whats 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 the individual researcher

How to carry out an opportunity sample?

Interviewer selects the sampling units according to the set criteria.

what are the advantages of a census?

completely accurate result

What are the disadvantages of a census?

• Time consuming

• expensive

• lots of data

• can’t be used when destroying things is involved

Advantages of a sample

• Cheaper

• quicker

• Less data to process

What are the disadvantages of a sample?

• Data may not be accurate

• Data may not be large enough to represent small subgroups.

Whats discrete quantitative data?

Numerical data that can only take specific values e.g. shoe size

Whats continuous quantitative data?

Numerical data that can take any possible decimal value