Levels of measurement and types of test

• Descriptive statistics


  • Describe the findings of research making it easier to interpret the data (mean, median, mode, SD, range)
  • Measures of central tendency and measures of dispersion
• Inferential statistics


  • Allow researchers to make inferences (draw conclusions) about whole populations based on smaller samples
  • Statistical tests
• Statistical analysis


  1. Collect data

  2. Identify the appropriate statistical test to use

  3. Work out a calculated value

  4. Compare this to a critical value to determine if the result is significant
• Nominal data


  • The data is in categories, can be tallied
  • Data is discrete, it can only appear in one category
  • A 'weak' form of data
  • Measure of central tendency = Mode
• Ordinal data


  • Data is ordered in some way/ it is numerical
  • Data does not have equal intervals between each unit
  • The data is in rank order and/or the data involves subjective human judgement e.g. rating scales rather than objective measurement
  • Memory is always ordinal because it is subjective
  • Measure of central tendency = median
• Interval data


  • Interval data is based on numerical scales that include units of equal, precisely defined size
  • The most precise and sophisticated and objective form of data in Psychology
  • Standardised scales
  • Measure of central tendency = mean
• Significance level


  • The point at which the researcher can claim to have discovered a significant difference between conditions in an experiment or a significant correlation
  • Psychologists generally use a level of significance of 0.05 or 5%
  • p≤0.05 - The probability of the result occurring by chance is less than or equal to 5%
  • The researchers is 95% confident that a 'real' result has been found
• N


  • The number of participants
  • In Chi-squared, Pearson's r and t-tests it is df (degrees of freedom)
• What is nominal data's measure of central tendency

  M
• What is ordinal data's measure of central tendency?

  Median
• What is interval data's measure of central tendency?

  Mean