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Flashcards in Stage 2 Deck (43)
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1
Q

Define sampling

A

A subset of items taken from the whole population (all the data available).

2
Q

When is sampling used?

A

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

3
Q

What are the 4 features of a good sample?

A
  1. Unbiased
  2. Precise
  3. Appropriate size
  4. Easily collected
4
Q

Features of a good sample:

unbiased

A

A sample where the mean and standard deviation of the sample is neither larger or smaller than the values for the whole population

5
Q

Features of a good sample:

precise

A

A sample that provides an accurate estimate of the population characteristics. It does not distort patterns/trends and does not exaggerate anomalies

6
Q

Features of a good sample:

Appropriate size

A

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.

7
Q

Features of a good sample:

Easily collected

A

Can be easily collected within the time/ equipment and researchers available

8
Q

What should a plan of a geographical investigation include?

A
  1. Sampling frame
  2. Sampling number
  3. Sampling Design
  4. Plan of timing/sampling/ division of labour
9
Q

Components of a plan of a geographical investigation;

Sampling frame

A

Sampling frame which clearly defines the outline of the area you will be investigating and a justification for choosing this area

10
Q

Components of a plan of a geographical investigation;

Sampling number

A

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

11
Q

Components of a plan of a geographical investigation;

Sampling design

A

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
12
Q

Define: sampling frame

A

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)

13
Q

Define: target population

A

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)

14
Q

Define: sampled population

A

Measurements for the area which is accessible to the investigation (e.g. pebbles which are exposed on the surface of the beach)

15
Q

Define: sample size

A

The number of measurements in a sample. For further statistical analysis this is usually a minimum of 30

16
Q

Define: population parameter

A

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

17
Q

Define: bias

A

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)

18
Q

Define: sampling error

A

The difference between a sample estimate and the population parameter

19
Q

Define: representative sample

A

A sample that minimised bias

20
Q

What are the three main types of spatial sampling?

A
  1. Point sampling
  2. Line sampling
  3. Area sampling
21
Q

spatial sampling - What is point sampling?

A

a selection of specific points within an area

22
Q

spatial sampling - What is line sampling?

A

sampling along a line through (e.g.) a city or across a sand dune

23
Q

spatial sampling - what is area sampling?

A

when an area is sub-divided into a selection of sample squares

24
Q

Sampling Type : Random

What is the method for random sampling?

A

Use number tables to generate random coordinates

25
Q

Sampling Type : Random

What are the advantages of random sampling?

A
  1. Least biased because every individual has equal chance of being selected
  2. Relatively quick and easy to select sample types
26
Q

Sampling Type : Random

What are the disadvantages of random sampling?

A
  1. May not take samples from a whole survey area
  2. Important variations may not be sampled and therefore you may not obtain a truly reliable sample
  3. Theoretically the same individual could be selected more than once
27
Q

Sampling Type : Systematic

What is the method for systematic sampling?

A

Samples are regularly spaced e.g. every 100m along a transect

28
Q

Sampling Type : Systematic

What are the advantages of systematic sampling?

A
  1. Quick and easy method
  2. Samples taken from all parts of the survey area so the whole area is covered
  3. No individual is selected more than once
29
Q

Sampling Type : Systematic

What are the disadvantages of systematic sampling?

A
  1. The regular interval may miss an important variation e.g. the top of the dune or a dune slack
  2. You may sample and evenly spaced characteristic which means the sample is unreliable because it over emphasises the importance of the regular feature
30
Q

Sampling Type : Stratified

What is the method for stratified sampling?

A
  • sampling frame divided into sub-sets
  • number of samples is taken from each subset in proportion to it’s relative importance
    (e. g. sand dunes is taken at a change of slope.)
31
Q

Sampling Type : Stratified

What are the advantages of stratified sampling?

A
  1. Can provide greater precision than a random sample

2. It requires greater precision, so often requires a smaller sample than for random sampling. This saves money.

32
Q

Sampling Type : Stratified

What are the disadvantages of stratified sampling?

A
  1. May be difficult to get background data to allow for reliable sampling
  2. Can introduce bias because researcher selects predetermined factors as being important e.g. land use or age/gender of population
33
Q

Sampling Type : Pragmatic

What is the method for pragmatic sampling?

A

Samples are only taken from areas which is safe or accessible

34
Q

Sampling Type : Pragmatic

What are the advantages of pragmatic sampling?

A
  1. Quick, easy and SAFE
35
Q

Sampling Type : Pragmatic

What are the disadvantages of pragmatic sampling?

A
  1. Will not take samples from the whole survey area so important variations may not be sampled
  2. May not obtain a truly reliable sample
  3. Bias is introduced
36
Q

What is a risk assessment?

A

identification and evaluation of the risks involved in undertaking research and the strategies that can be taken to minimise these risks

37
Q

What is a physical risk?

A

risks of harm or injury to the researchers caused by the environment

38
Q

What is a statistical risk?

A

A risk that the data collected does not accurately represent the whole population because of bias in the sampling technique or errors in data collection.

39
Q

When are statistical risks introduced into an investigation?

A

Statistical risk is introduced into an investigation when:

  1. Insufficient samples are taken or the sampling technique is not well planned so that not all the population is represented in the same sample
  2. Data collection methods can cause risk when the equipment is inaccurate or the researchers lack precision
40
Q

Name 5 methods for reducing statistical risks :

A
  1. Sufficient samples need to be taken and the samples must cover as much of the sample frame as possible
  2. The sample size must be large enough for statistical testing to be used with confidence. A sample size of at least 12 is needed
  3. A careful balance between the number of samples needed and the time/researchers available must be made
  4. Highly accurate equipment must be used
  5. Researchers must be trained so that they can use the equipment accurately
41
Q

Pilot Survey

What is a pilot survey?

A

A prior visit to the investigation site or practising your questionnaires with friends/family prior to the real investigation

42
Q

Pilot Survey

What are the advantages of a pilot survey?

A
  1. To assess the accessibility of the site
  2. To assess the physical risks of the site
  3. To practise data collection methods to ensure more accuracy
  4. To make sure that the sampling techniques and data collection methods selected will result in the required data being collected for the investigation
  5. To help refine data collection sheets
  6. To identify any unforeseen risks both physical and statistical
43
Q

Pilot Survey

What are the disadvantages of a pilot survey?

A
  1. Time consuming
  2. Costly
  3. Might be hard to access location