Standard Deviation

• S.D

  • different distributions have the same mean average, mode and medians but they have different spreads
  • measures amount of variability/spread of individual data values to the mean
  • to measure spread, you could use range but this includes anomalies so can create a wrong impression but s.d is a measure of the spread about the mean which is a better measure of the spread as its less affected by outliers

  
• Results from S.D

  • if s.d's overlap, the difference in means is small and therefore not significant so the differences in the means are likely to be due to chance
  • ALWAYS MEASURE 2 S.D's - TIMES S.D BY 2
  • then do mean + (2xS.D) and mean - (2xS.D)
• Standard Deviation

  • describes variability within a single sample
• Standard Error of Mean

  • estimates variability across multiple samples of a population - mean could differ each time depending on the sample
• Error Bar


  used on graph to represent standard deviation