Chapter 5: Describing Distributions Numerically Flashcards Preview

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Flashcards in Chapter 5: Describing Distributions Numerically Deck (6)
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1
Q

What are some ways to compare distributions?

A
  • 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.
2
Q

How should we treat outliers?

A

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.
3
Q

What can re-expression of data do and what are some ways to do it?

A
  • 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.
4
Q

When comparing the distributions of several groups using histograms or stem-and-leaf displays, consider their…?

A
  • Shape
  • Centre
  • Spread
5
Q

When comparing groups with boxplots, compare the…?

A

-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.

6
Q

Define ‘Timeplot’.

A

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.