Stage 2 Flashcards
Define sampling
A subset of items taken from the whole population (all the data available).
When is sampling used?
It is used when:
•The population is too large to study each individual
•Time is limited
•Collecting data is destructive and you are trying to minimise damage
What are the 4 features of a good sample?
- Unbiased
- Precise
- Appropriate size
- Easily collected
Features of a good sample:
unbiased
A sample where the mean and standard deviation of the sample is neither larger or smaller than the values for the whole population
Features of a good sample:
precise
A sample that provides an accurate estimate of the population characteristics. It does not distort patterns/trends and does not exaggerate anomalies
Features of a good sample:
Appropriate size
A sample that is large enough to produce conclusive results in terms of statistical significance (a sample size of over 12 is considered large enough for making reliable conclusions using statistical testing e.g. Spearman’s Rank), but small enough to be done well.
Features of a good sample:
Easily collected
Can be easily collected within the time/ equipment and researchers available
What should a plan of a geographical investigation include?
- Sampling frame
- Sampling number
- Sampling Design
- Plan of timing/sampling/ division of labour
Components of a plan of a geographical investigation;
Sampling frame
Sampling frame which clearly defines the outline of the area you will be investigating and a justification for choosing this area
Components of a plan of a geographical investigation;
Sampling number
Sampling number which is sufficient to provide a reliable sample but practical for collecting within the time scale and with the number of researchers available
Components of a plan of a geographical investigation;
Sampling design
Sampling design which clearly describes and justifies the choice of sampling technique employed.
- Sampling type could be grid, point or transect
- Sampling strategy could be random, systematic, stratified or pragmatic
- It is advisable to draw a sketch of the area to show the locations of the sampling sites
Define: sampling frame
The study area or group from which the sample is selected (e.g. area on an OS map, electoral register, telephone directory, every person entering a shopping centre)
Define: target population
Total set of measurements relevant to a study (e.g. all possible measurements of pebble size from a beach which are useful for the investigation)
Define: sampled population
Measurements for the area which is accessible to the investigation (e.g. pebbles which are exposed on the surface of the beach)
Define: sample size
The number of measurements in a sample. For further statistical analysis this is usually a minimum of 30
Define: population parameter
A true summary measurement of the characteristics of the target population (e.g. mean size of pebbles on a beach). If the parameter is based on a sample, it is only an estimate
Define: bias
This occurs when the sample measurement over- or under-estimates the population parameter. May be introduced unconsciously (e.g. including certain places because they are more accessible or interviewing a certain age group/gender of shoppers because of the time of day/day of the week)
