Chapter 1 - Collection of Data

• Random Sample

  Every item/person has an equal chance of being selected.

  Advantages : representative, unbiased

  Disadvantages : need sample frame, can be expensive and time consuming, needs a large sample size
• Stratified sample

  the size of each strata (group) in the sample is in proportion to the sizes of strata in the population.

  Advantages : represents population fairly, best used for groups with unequal sizes

  Disadvantages : time consuming
• Systematic sampling

  choosing items in the population at regular intervals

  Advantages : population evenly sampled, machine can be used, sample is easy to select

  Disadvantages : not strictly random sample
• Cluster sampling

  the population is divided into natural groups, groups are chosen at random and every member of groups are sampled. useful for large populations

  Advantages : economically efficient - less resources required, can be representative (if small clusters sampled)

  Disadvantages : may not be representative (could be biased), high sampling error
• Quota sampling

  population grouped by characteristics and a fixed amount is sampled from every group

  Advantages : quick to use, cheap, don't need a sample frame

  Disadvantages : not random - BIASED
• Opportunity sampling

  using the people/items that are available at the time

  Advantages : quick, cheap, easy

  Disadvantages : not random - BIASED
• Judgement sampling

  when the researcher uses their own judgement to select a sample, they think will represent the population

  Advantages : easy, quick

  Disadvantages : not random - BIASED, may be unreliable
• Petersen Capture-recapture

  first capture/total = tagged/second capture
• Variables

  Explanatory (independent) - variable that changes

  Response (dependent) - variable that is measured

  Extraneous - variables that you are not interested in but could affect the result of your experiment
• Laboratory experiments

  researcher has full control over variables. Conducted in a lab or similar environment

  Advantages : easy to replicate (more reliable results), extraneous variables can be controlled (more valid results)

  Disadvantages : people may behave differently under test conditions (could affect validity of results)
• Field experiments

  carried out in everyday environment. Researcher has some control over variables. They set up the situation and controls the explanatory variable but has less control over extraneous variable.

  Advantages : more accurate - reflects real life behaviour

  Disadvantages : cannot control extraneous variables, not as easy to replicate (less reliable)
• Natural experiments

  carried out in everyday environment. Researcher has little/no control over variables.

  Advantages : reflects real life behaviour

  Disadvantages : low validity, difficult to replicate, cannot control extraneous variables
• Simulation

  A way to model random events using random numbers and previously collected data. Could be used to help you predict what could actually happen in real life.