Statistical Tests

• In the biology A-level exam, you will not be asked to calculate standard deviation as it takes too long to be assessed in an exam
• Standard deviation


  A measure of how spread out all your repeats are from your mean
• You could be asked what the purpose of standard deviation is in the exam
• Key reasons why standard deviation is more useful than range


  • Standard deviation shows the spread of data around the mean, whereas the range only shows the highest and the lowest
  • The effects of anomalies are reduced with standard deviation compared to range
  • Standard deviation can be used to indicate whether a difference between the results is likely to be significant
• Significant difference


  If when you've either added or minus the standard deviation from your means, there is no overlap between the two groups or more than two groups that you're pairing, it's likely that the difference between them is significant
• If when you add or minus a standard deviation from the mean there's overlap, it indicates that there is likely not to be a significant difference
• If when you add or minus a standard deviation from the mean there's no overlap, it indicates that there is likely to be a significant difference
• Evaluating a conclusion using standard deviation


  1. Look for overlap in the standard deviation bars

  2. If there is overlap, it indicates there is likely no significant difference

  3. If there is no overlap, it indicates there is likely a significant difference
• The standard deviations for plant species A and C overlap, indicating there is likely no significant difference in mean glucose production per minute
• The standard deviation for plant species B does not overlap with A or C, indicating it is likely to be significantly different, and significantly lower