Words

• Population


  A collection of all the items
• Sample


  A selection of the population to use data from
• Census


  When data is taken from every member in the population
• Advantages of a census over a sample


  More representative, less biased, includes everyone's opinions
• Advantages of a sample over a census


  Quicker, cheaper, easier to analyse as less data
• Disadvantages of a census over a sample


  Time consuming, expensive, difficult to do
• Disadvantages of a sample over a census


  Less representative, possibly biased
• Pilot Study


  A small scale replica of the survey to be carried out.
• Advantages of a pilot study


  Ensures questions can be understood, identify ambiguity, test response rate, identifies likely responses, check methods
• Sampling Frame


  A list containing data that a sample can be taken from
• Examples of a sampling frame


  Electoral role, SIMS register, DVLA, telephone directory
• Primary Data


  Data that has been collected by the person doing the survey
• Secondary data


  Data that hasn't been collected by the person doing the survey
• Advantages of primary data

  More reliable, up-to-date, tailored for investigation
• Advantages of secondary data

  Easier to obtain, cheaper, less time-consuming
• Continuous Data


  Data that lies on a continuous scale (can be at any point on a number line)
• Discrete Data


  Data that consists of separate numbers (jumps along the number line)
• Quantitative Data


  Data that has numerical values
• Qualitative Data


  Data that is not numerical values
• Open Questions


  Has no suggested answers and has freeform boxes to reply in
• Advantages of open questions


  Allows for a range of responses, so can cover all eventualities
• Closed Questions


  Has a set of answers for the person to choose from
• Advantages of closed questions

  Easier to analyse as range of responses restricted
• Leading Questions


  Questions that infer an opinion and promote a certain answer
• Random Sample


  Each person has an equally likely chance to be picked
• How to take a random sample

  (a) Number everyone in list

  (b) Use a random number generator to select numbers

  (c) Select the data points corresponding to the numbers picked

  (d) If you get a number outside the range or the same number twice you repeat, if you get a decimal round to the nearest number.
• Advantages of a random sample


  Easy to do
• Disadvantages of a random sample


  May not be representative
• Systematic Sample


  Data is chosen at regular intervals (e.g. every 10th person)
• How to take a systematic sample


  Order population and divide population by sample size to find how often data chosen. Then choose random number to decide where in this interval to start.
• Advantages of a systematic sample


  Useful for production line - will spot problems over time
• Disadvantages of a systematic sample


  May not be representative
• Quota Sample


  The same amount of people from different chosen groups are sampled
• How to take a quota sample


  Decide on a quota size for each group. Then take a random sample, ignoring any results from a group where the quota has been reached.
• Advantages of a quota sample


  Makes sure all quota groups are represented, easy to take
• Disadvantages of a quota sample


  Not likely to be representative, may be difficult to reach quota if numbers limited
• Cluster Sample


  The population is divided into groups and a group is chosen at random.
• Advantages of a cluster sample

  Easy to do
• Disadvantages of a cluster sample


  Unlikely to be representative
• Stratified Sample


  Where the data sampled in each group is proportional to that of the whole population