Estimation from Statistical Data (Edexcel GCSE Statistics)

Estimating Population Characteristics

How can I use samples to estimate population characteristics?

• Summary statistics calculated from a sample can be used to estimate the same statistics for the population as a whole

  • e.g. the mean, median, range, quartiles and interquartile range

• Remember that a sample is a selection of members drawn from the population, whereas the population is all the members

  • Statistics calculated from a sample will usually not be exactly the same as the statistics for the whole population (different mean, etc.)

  • Statistics calculated from two different samples will also not usually be the same

• As long as the sample is representative of the population

  • then you can assume that the statistics for the population are approximately the same as those for the sample

    • e.g. assume the population mean is about equal to the sample mean

• This can be used to make predictions about the population

  • About half (50%) of the population will be above the sample median

    • and about half will be below

  • About a quarter (25%) of the population will be below the sample lower quartile

    • and about a quarter will be above the sample upper quartile

  • About half (50%) of the population will be between the sample upper and lower quartiles

• Sample size has an impact on the reliability of estimates made about the population

  • In general a larger sample size will lead to more reliable conclusions