Large Data Sets - Statistics Flashcards
Name 5 sampling techniques
Simple random sampling
Systematic sampling
Stratified sampling
Quote sampling
Opportunity (or convenience) sampling
What is random sampling and how is it carried out?
Every sample has an equal chance of being selected.
You assign a number to each sample and then use a random number generator
What are the advantages to random sampling?
Bias Free
Easy and cheap to implement
Each number has a known equal chance of being selected
What are the disadvantages of random sampling?
Not suitable when the population size is large
Sampling frame is needed
What is systematic sampling?
When required elements are chosen at regular intervals in ordered list
How do you determine every Kth element in the systematic sampling method?
K=population size/ sample size
What are the advantages to systematic sampling?
Simple and quick to use
Suitable for large samples/populations
What are the disadvantages to systematic sampling?
A sampling frame is needed
Can introduce bias if the sampling frame is not random
What is stratified sampling?
The population is divided into groups (strata) and a simple random sample is carried out in each group.
When is stratified sampling used?
When the sample is large and the population naturally divided into groups
What are the advantages of stratified sampling?
Reflects the population structure
Guaranteed proportional representation of groups within the population
What are the disadvantages of stratified sampling?
The population must be clearly classified into distinct strata.
Selection within each stratum suffers from the same disadvantages as simple random sampling
E.g. not suitable for large population size, sampling frame is needed
How do you get the same proportion sampled in each strata in stratified sampling?
Sample size/population size
What is quota sampling?
When the population is divided into groups according to characteristics. A quota of items/people in each group is set to try and reflect the group’s proportion in the whole population. Interviewer selects the actual sampling units
What are the advantages of quota sampling?
Small sample still represents the population.
No sampling frame required
Quick, easy, inexpensive
Allows for easy comparison between different groups in population
What are the disadvantages of quota sampling?
Can introduce bias
Costly or inaccurate to divide the population into groups
Increasing the scope of the study increase the number of groups which adds time/expense
Non responses are not recorded
What is opportunity sampling?
A sample taken from people who are available at the time of study, who meet criteria
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 types of data are there?
Qualitative
Quantitative
What are the two types of quantitative data?
Discrete
Continuous
When was the data from the large data set recorded for?
May-Oct 1987
May-Oct 2015
What are the names of the 5 UK weather stations?
Heathrow
Camborne
Leuchars
Lemming
Hurn
What are the names of the three international weather stations?
Jacksonville
Beijing
Perth
