11 - 8 SAMPLES AND SURVEYS

Definition of Terms:

  • POPULATION

    • This represents all the members within a set.

  • SAMPLE

    • Represents a part of the population.


Types of Sampling:

  • SELF-SELECTED (BIASED)

    • Select only the members of a population who volunteer for the sample. 

  • SYSTEMATIC (LESS BIASED)

    • Selected from a regular interval from a population. 

  • RANDOM (LESS BIASED)

    • Selected from from the population where each member has an equal chance to be chosen.

  • CONVINIENCE (BIASED)

    • Conveniently selected/readily available. 


Systematic Error! 

  • BIAS

    • A systematic error where a population is underrepresented/overrepresented. 

Sampling Method

Biased or Unbiased?

Reason

Self-Selected

Biased

Volunteers choose themselves; tends to overrepresent strong opinions.

Convenience

Biased

Only includes those easily accessible; not representative of the population.

Systematic

Usually Unbiased

Every nth member is chosen; unbiased if no hidden pattern in the population list.

Random

Unbiased

Each member has an equal chance of selection; best for representation.