Chapter 8 - Probability Distributions

• Binomial distributions

  only 2 possible outcomes

  B(n,p) n = number of trials p=probability of success

  conditions:
• Normal distribution

  drawn as a smooth bell-shaped curve

  N(mean, square of sd)

  Conditions:

  • data is continuous
  • distribution is symmetrical
  • mode median and mean are all approximately equal
• Properties of normal distribution

  1 standard deviation of the mean = 68%

  2 standard deviation of the mean = 95%

  3 standard deviation of the mean = 99.8%
• number of SD from mean = (value-mean)/standard deviation
• standardised score = (score-mean)/standard deviation
• Quality assurance

  checking samples to make sure products are all of the same quality and standard
• control chart

  a time series chart used for quality assurance

  • Target value : middle line
  • Upper and lower warning lines (inner 2 lines) - 2SD above and below target
  • Upper and lower action limits (outer 2 lines) - 3SD above and below the target value