Data Collection Flashcards
What is a Census?
A census measures or observes every member of a population.
what are the ADVANTAGES of a census?
Gives accurate results
What are the DISADVANTAGES of a Census?
- Time consuming and expensive
- Cannot be used in destructive testing
- Hard to process large quantity of data
What is a Population?
Whole set of items that are of interest
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.
Generally the larger the sample the more accurate.
What are the ADVANTAGES of a Sample?
-Less time consuming and expensive than a census
- Fewer people have to respond
- Less data to process than a census
What are the DISADVANTAGES of a Sample?
- Data may not be as accurate
- Sample may not be as large enough to give information about sub groups of the population
What are sampling Units?
Individual units of a population
e.g taking a sample in the sixth form, I am a sampling unit.
What is a sampling Frame?
A sampling frame is where sampling units of a population are individually named or numbered to form a list.
What are the 3 types of Random Sampling?
- Simple Random Sampling
- Systematic Sampling
- Stratified Sampling
What is Simple Random Sampling?
A sampling Frame is required, each person or thing is allocated a number for random selection.
- either generating random numbers (computers, tables),or lottery sampling
- Lottery sampling - sampling frame or units can be written on tickets or put in a hat
What are the 2 types of methods for Simple Random Sampling?
Either generating random numbers (computers, tables), or lottery sampling
What are the ADVANTAGES of Simple Random Sampling?
- No bias
- Easy and cheap to implement for samples
- Each sampling unit has a known and equal chance of selection
What are the DISADVANTAGES of Simple Random Sampling?
Not suitable when the population or sample size is large - Time consuming
- Sampling frame is needed.
What is Systematic Sampling?
The required elements are chosen at regular intervals from ordered list.
E.g Sample size of 20 from a populations of 100. k = 5 choose value from 1-5 and pick a number every 5th value
K = Population Size (N) / Sample Size (n)
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 required
- if the sampling frame is not random there can be bias.
What is Stratified Sampling?
Population is divided into mutually exclusive strata and a random sample is taken from each.
Sample Size (n) / Population (N)
What are the ADVANTAGES of Stratified Sampling?
- Accurately reflects the population structure.
- Guarantees proportional representations of groups within a population.
What are the DISADVANTAGES of Stratified Sampling?
- Population must be clearly classified into a distinct area
- Selection of each stratum suffers from the same disadvantages as simple random sampling.
What are the 2 types Non - Random Sampling?
Quota Sampling
Opportunity sampling
what is Quota Sampling?
Interviewer or researcher selects a sample that reflects the characteristics of the whole population.
A quota of items/people in each group is set to reflect the groups proportion in the whole population - interview sets the actual sampling unit.
What are the ADVANTAGES of Quota Sampling?
No sampling frame required
- Not expensive
- Allos for easy comparison between groups
- Allows for a small sample to still be representative of the population.
What are the DISADVANTAGES of Quota Sampling?
- Can introduce Bias
- Population has to be divided into groups
- Non responses are not recorded
What is opportunity SAmpling/Convenience Sampling?
- Taking sample from who are available at the time of study who meet the criteria.
What are the ADVANTAGES of Opportunity Sampling?
- Quick and easy
- Inexpensive
What are the DISADVANTAGES of Opportunity Sampling?
- Bias can be introduced
- Unlikely to provide representative sample
- Very dependent on individual researcher.
What is a Quantitative variable?
Variables associated with numerical observations
e.g shoe size
What is a Qualitative variable?
A variable or data associated with Non-Numerical observations
e.g hair colour
What is a continuous variable?
A variable that can take any value in a given range
e.g time , 2 seconds, 0.2 seconds
What is a Discrete variable?
A variable that can take only a specific value ina a given range
e.g numbers of girls in a family can be 2.65
What are the 5 weather stations in the UK
From South to North?
Camborne
Hurn
Heathrow
Leeming
Leauchars
What are the 3 International Weather Stations?
Perth, Australia - southern hemisphere
Bejing, China
Jacksonville USA
What is the Daily Mean Temperature?
Average of hourly temperatures during a 24-hour period
degrees Celsius
Daily Total Rainfall
Includes precipitation such as hail and snow melted before being included in any measurement.
What is Trace (tr)
when rainfall is less than 0.05mm.
Daily Total Sunshine
Recorded to the nearest tenth hour.
Daily Mean Wind Direction And Windspeed
Averaged over 24 hrs
Mean wind directions are given as bearings.
Data on mean windspeed is categorised according to Beaufort Scale.
Measured in Knots
1 Knot = Nautical Mph
What is 1 Knot equivalent to?
1 Knot = 1.15 mph
Daily Max relative humidity
Measured in Knots
Humidies above 95% give rise to misty and foggy conditions.
Daily Mean Cloud Cover?
Measured Oktas or eighths or the sky covered by clouds.
Daily Mean Visibility?
Measured in Decametres (Dm)
The greatest horizontal distance at which an object can be seen in the daylight.
Daily mean Pressure?
Measured in Hectopascals (hpa)
What does N/A mean?
Not Available
