Describing data - Median and interquartile range
10 important questions on Describing data - Median and interquartile range
What is, after the sample mean, the next most common used metric to describe distributions?
What kind of observation is the median, and what is it's function?
How is the median calculated? Take into account a dataset with 1. Odd numbers of observations and 2. Even number of observations.
- If the number of observations is odd, then the median is the middle observation by [n+1]/2
- If the number of observations is even, then the median is the average of the middle pair: ((n/2)+(n/2+))/2
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The median is the 50th percentile and the 0.5 quantile, why?
The 0.5 quantile is the value below which 0.5 of the individual values lie.
What do quartiles do with the data?
Describe what the first, second and third quartile point out on the frequency distribution, give the percentiles.
- First quartile, 25th percentile, is the middle value of the measurements lying below the median.
- Second quartile, 50th percentile, is the median.
- Third quartile, 75th percentile, is the middle value of the measurements above the median.
How is the interquartile range calculated?
- Break the data in half (leave out the median when n is odd)
- First and third quartiles are calculated as the mean.
- Interquartile range = third quartile - first quartile
!This is a value that points out the range of the data in the units of the data, f.e. For weight it will be 50kg.
What does the box of a box plot display of a frequency distribution?
What do the whiskers of a box plot show?
What is extreme value of a dataset? How are they plotted in a box plot?
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