Chapter 5: Describing Distributions Numerically Flashcards
What are some ways to compare distributions?
- Compare distributions of 2 or 3 groups with histograms.
- Compare several groups with boxplots, which make it easy to compare centres and spreads and spot outliers, but hide much of the detail of distribution shape.
How should we treat outliers?
With attention and care.
- When we group data in different ways, different cases may emerge as outliers.
- Track down the background for outliers - it may be informative.
What can re-expression of data do and what are some ways to do it?
- Re-expression can make skewed distributions more nearly symmetric.
- Re-expression can make the spreads of different groups more nearly comparable.
- For right-skewed data, try sqrt, logs, or reciprocals. For left-skewed data, try squaring or exponential function.
When comparing the distributions of several groups using histograms or stem-and-leaf displays, consider their…?
- Shape
- Centre
- Spread
When comparing groups with boxplots, compare the…?
-Compare the shapes. Do the boxes look symmetric or skewed? Are there differences between groups?
-Compare the medians. Which group has the higher centre? Is there any pattern to the medians?
-Compare the IQRs. Which group is more spread out? Is there any pattern to how the IQRs change?
Using the IQRs as a background measure of variation, do the medians seem to be different, or do they just vary in the way that you’d expect from the overall variation?
-Check for possible outliers. Identify them if you can and discuss why they might be unusual. Of course, correct them if you find that they are errors.
Define ‘Timeplot’.
A timeplot (often called a time series plot) displays data that change over time. Often, successive values are connected with lines to show trends more clearly. Sometimes a smooth curve is added to the plot to help show long-term patterns and trends.
