Choosing a Statistical Test

• 3 levels of measurement


  nominal, ordinal interval
• nominal data


  named distinct categories
• ordinal data


  data that is ordered in some way, but the actual value of the figure isn't measurable
• interval data


  measured along a scale (that has units) where the distance between one value and the next is equal and standardised
• 3 factors used to decide which statistical test to use


  -difference

  -design

  -data
• two experimental designs known as related


  repeated measures and matched pairs design
• criteria for using a parametric test


  -interval data

  -population is normally distributed

  -variance between two samples is not statistically significant