Chapter 1 - Data collection Flashcards
What is a population?
The whole set of items that are of interest
What is a sample?
The subset of the population intended to represent that population
What is a sampling unit?
Each individual thing in a population that can be sampled
What is a sampling frame?
A list of individually named or numbered sampling units
What is a census?
An observation or measurement of the whole population
Advantages of using a census
The result should be completely accurate
Disadvantages of using a census (3)
Time-consuming and expensive
Can’t be used when the testing process destroys the item
Hard to process the large amounts of data obtained
What is a sample?
A selection of observations taken from a subset of the population which is used to find out information about the population as a whole
Advantages of using a sample (3)
Fewer people have to respond
Less data to process
Less time-consuming and expensive
Disadvantages of using a sample (2)
The data may not be as accurate
The sample might not give information about small sub-groups of the population
What are the three methods of random sampling?
Simple random sampling, stratified sampling and systematic sampling
What is simple random sampling?
Every sample has an even chance of being selected
How to conduct a simple random sample?
Number each item and use a random number generator
Advantages to simple random sampling (3)
No bias
Easy and cheap to implement
Each unit has a known and equal chance of selection
Disadvantages to simple random sampling (2)
Not suitable when the population size is large - too time-consuming
A sampling frame is needed
What is systematic sampling?
Required elements are chosen at regular intervals from an ordered list
How to conduct a systematic sample
Take every nth element, where n = population size / sample size
Advantages of systematic sampling (2)
Simple and quick
Suitable for large population/sample sizes
Disadvantages of systematic sampling (2)
A sampling frame is needed
It can introduce bias if the sampling frame isn’t random
What is stratified sampling?
The population is divided into strata and a random sample is carried out for each strata
Advantages of stratified sampling (2)
The sample accurately reflects the structure of the population
It guarantees a proportional representation of groups within a population
Disadvantages of stratified sampling (2)
The population must be clearly divided into strata
Selection from each stratum suffers the same disadvantages of simple random sampling (e.g. a sampling frame is needed ad it isn’t suitable when the sample size is large)
What is quota sampling?
A researcher selects a sample that reflects the characteristics of the whole population
How to conduct quota sampling
Divide the population into groups according to the characteristic of interest, then determine the size of each group in the sample so it is representative
What is opportunity sampling?
Taking the sample from people who are around at the time the study is carried out and who fit the criteria you are looking for
Advantages of quota sampling 3
No sampling frame required
Quick, easy and inexpensive
Easy comparison between different groups
Disadvantages of quota sampling 3
Can introduce bias
Dividing the population into groups can be inaccurate or costly
Non-responses aren’t recorded
Advantages of opportunity sampling 2
Easy to carry out
Inexpensive
Disadvantages of opportunity sampling 2
Unlikely to be representative
Highly dependent on the researcher
What is qualitative data?
Data associated with words
What is quantitative data?
Data associated with numbers
What is a continuous variable?
Can take any decimal value in a range
What is a discrete variable?
Can only take specific whole numbers
What are class boundaries?
The minimum and maximum values in a class
What is the midpoint?
The average of the class boundaries
What is the class width?
The difference between the upper and lower class boundaries
What is the daily mean temperature?
The average of the hourly temperature readings during a 24 hour period
What is the daily total rainfall?
The amount of precipitation which falls in a day
To what unit is the daily total sunshine recorded to?
The nearest tenth of an hour
What is daily windspeed measured in?
Knots
What is the daily maximum gust?
The highest instantaneous windspeed recorded
What will humidities above 95% result in?
Misty and foggy conditions
What is daily mean cloud cover measured in?
Eighths of the sky covered by cloud
What is the daily mean visibility?
The greatest horizontal distance at which an object can be seen in daylight
Where are the five UK weather stations?
Leeming Leuchars Camborne Heathrow Hurn
Where are the three international weather stations?
Beijing
Jacksonville
Perth
