Notes for comment questions
When exam questions ask you to comment on something, there is a standard, small, list of things that they are looking for. Make some notes about these as we go along.
Histograms:
- Are good for continuous data, which is then grouped into classes
- the vertical axis is the frequency density, frequency divided by class width
- The class width goes to half way between the end of this class and the beginning of the next, if the class boundaries aren't the same.
Scaling rules:
- mean(ax)=a.mean(x) - if the points are twice as big, so is the average
- stdev(ax)=a.stdev(x) - if the points are twice as big, they are twice as spread out.
- mean(x+a)=mean(x)+a - if you move all the points further along the axis, the mean is moved too
- stdev(x+a)=stdev(x) - if you move all the points further along the axis, they are still as spread as they were
box plots
- Show quartiles and median
- Show outliers
- Show skew
- Are good for comparing two datasets
