Normal Distribution

• normal distributions have a symmetrical distribution
• normal distributions are the idealised perfect distribution
• two properties of a normal distribution

  mean defines the position, sd defines the spread
• 68% of all observations lies in 1SD from the mean both ways
• 16% of the data lies outside 1SD of the mean
• 95% of the data lies within 3SD of the mean
• z score


  measured in term of sd from the mean
• z score is how many sd a value is away from the mean
• What would be the z score for 0.83?

  0.7967

  
• z scores can be used to calculate the proportion of values above and below particular values
• skewness

  A) right skew

  B) left skew

  
• right skews have the tailing end on the right
• left skews have the tailing end on the left
• left skews will have the mean to to the left of the median
• right skew will have the mean the to right of the median