Data Collection

• Define Population:

  The whole set of items that are of interest
• Define Raw Data:

  Data obtained from a population
• Define Census:

  Data that measures every member of a population
• Define Sample:

  A selection of observations taken from a subset of the population used to estimate information about the population as a whole
• Outline the advantage of a census:

  • It gives a completely accurate result
• Outline the disadvantages of a census:

  • Time consuming
  • Expensive
  • Cannot be used when the testing process destroys the items
  • It is difficult to process a large quantity of data
• Outline the advantages of a sample:

  • Less time consuming
  • Cheaper
  • Fewer responses are needed
  • Less data is processed
• Outline the disadvantages of a sample:

  • Data may not be as accurate
  • The sample may not be large enough to be representative of the whole population
• Define Sampling Units:

  The individual units of a population
• Define Sampling Frame:

  Sampling units individually named or numbered to form a list
• Name the three types of random sampling:

  • Simple random sampling
  • Systematic sampling
  • Stratified sampling
• Define Simple random sampling:

  A sampling technique where every element in the set has an equal chance of being selected
• Define Systematic sampling:

  A sampling technique where the elements are chosen at regular intervals from an ordered list
• Define Stratified sampling:

  A sampling technique where the population is divided into exclusive strata and a random sample is taken from each
• Outline the advantages of simple random sampling:

  • Non-bias
  • Easy and cheap for small samples and populations
  • Each sampling unit has a known and equal chance of being selected
• Outline the disadvantages of simple random sampling:

  • Not suitable for large samples and populations
  • Sampling frame needed
• Name the two methods of choosing the numbers from a sampling frame in simple random sampling:

  • Generating random numbers
  • Lottery sampling
• Describe how a calculator is used for generating random numbers for simple random sampling:

  Each sampling unit from a sampling frame is numbered.

  Use a calculator to generate a set of numbers.

  Select the sampling units who correspond to the numbers generated.
• Describe how lottery sampling is used for simple random sampling.

  The sampling units from a sampling frame are written on identical cards.

  The cards are put into a hat.

  The required number of sampling units needed are drawn from the hat.

  The card of the sampling unit drawn out are selected.
• Outline the advantages of systematic sampling:

  • Simple and quick to use
  • Suitable for large samples and populations
• Outline the disadvantages of systematic sampling:

  • Sampling frame needed
  • Can be biased if the sampling frame is not random
• The formula for how to work out the value of the regular intervals for systematic sampling:

  The population / the sample size
• The first person selected in systematic sampling is chosen randomly, then the regular intervals continue
• Outline the advantages of stratified sampling:

  • Accurately reflects population structure
  • Guarantees proportional representation of all groups within a population
  • analyse specific groups within a population
  • observe relationships between groups
• Outline the disadvantages of stratified sampling:

  • The population must be clearly classified into distinct strata
  • Same disadvantages as simple random sampling within each stratum
• Name the two types of non-random sampling:

  • Quota sampling
  • Opportunity sampling
• Define Quota sampling:

  A sampling technique where the sample selected reflects the characteristics of the whole population
• Define Opportunity sampling:

  A sampling technique where the sample is taken from people who are available at the time of study and who fits the criteria needed
• Outline the advantages of quota sampling:

  • Allows a small sample to be representative of the whole population
  • No sampling frame needed
  • can be quick
  • can be easy
  • can be cheap
  • Allows comparisons between different groups within the population
• Outline the disadvantages of quota sampling:

  • Bias
  • The population must be divided into groups which can be inaccurate - not possible to estimate sampling errors
  • A more in depth study can be time consuming as it increases the number groups
  • Non-responses are not recorded
• Outline the advantages of opportunity sampling:

  • Easy
  • Cheap
• Outline the disadvantages of opportunity sampling:

  • Results can be unrepresentative of the whole population
  • Highly dependent on the individual researcher
• Define Qualitative data:

  Non numerical data
• Define Quantitative data:

  Numerical data
• Define Discrete data:

  Data which can only take specific values
• Define Continuous data:

  Data which can take any value in a given range
• What is the limitation for continuous data?

  How accurately it is measured
• Define Class boundaries:

  The maximum and minimum values in each group
• Define the Midpoint:

  The mean/ average of the class boundaries
• Define the Class Width:

  The difference between the upper and lower class boundaries