BIO3011 Lecture Notes - Lecture 2: Confidence Interval, Summary Statistics, Standard Error
31 May 2018
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2. Summary statistics – dealing with uncertainty:
• We estimate population parameters (mean and SD) from a sample of data
• Sampling is influenced by chance
• Increasing the sample size reduces the spread of the distribution of an estimate, increasing the
precision (high precision = low uncertainty)
• Standard error (SE):
o Quantifies the uncertainty around an estimate
o Reflects precision
o Small SE = more precise
o Large SE = less precise
• Confidence interval (CI):
o Another way to quantify uncertainty about the value of the parameter
o Range of numbers that are likely to contain within its span, the value of the target
parameter
o Values lying within interval = most plausible
o Values outside interval = less plausible
o Broad CI = uncertainty is high and data is not very informative about location of mean
o Narrow CI = can be confident that parameter is close to estimated value
o Eg. We are 95% confident that the population mean lies within the 95% CI
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