Download Using Statistics in Biology

Using Statistics in Biology
Histogram
Mean (x̄) is a measure of the central tendency
of a set of data.
Ex. Calculate the mean.
Answer = 11.6
Graphing the Mean  Bar Graph
Error bars are a graphical representation of the
variability of data.
Measures of Variability
• Range: difference between largest/smallest
values in data set
• Standard deviation (s) is a measure of the
spread of most of the data
• 68% of all data fall within ± 1 standard deviation of
the mean
• 95% of all data fall within ± 2 standard deviation of
the mean
Measurements of Confidence
Uncertainty: the margin of error in a measurement
– Eg. digital scale: 126.4g (±0.1g)
• Standard Error of the Mean (SE or SEM):
measures how close the sample mean is to the
population mean
• The greater the sample size, the less the
uncertainty in the calculations
95% confidence interval (95% CI):
•95% confident that the true means falls
between 2 SE above/below calculated mean
Graph with error bars
representing SE of the mean
Graph with error bars representing
95% confidence interval
Significance of Data
Which graph shows two means that are
significantly different?
Hint: Look for the non-overlapping error bars.
Answer: The means in (c) are statistically different.