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Discussing Samples

Discussing Samples. Discussion of a sample - using USSCSI When describing sample distribution use these headings: -  I nitial Visual Interpretation -  S hape (Symmetry, Skew, Tail) -  C entre -  S pread -  S hift/Overlap -  U nusual Features (gaps, outliers).

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Discussing Samples

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  1. Discussing Samples

  2. Discussion of a sample - using USSCSIWhen describing sample distribution use these headings:- Initial Visual Interpretation- Shape (Symmetry, Skew, Tail)- Centre- Spread- Shift/Overlap- Unusual Features (gaps, outliers)

  3. When describing dot plots: discuss symmetry, skew, outliers, gaps, clusters • Also consider possible reasons or causes of these features (in the context) • Symmetry - Is the data symmetrical either side of the median? Or is one side more spread out? • Outliers - Decide if they are outliers or not? Will they impact the data? • Gaps - A small gap is of no concern, but a large gap may reflect groups or underlying variables • Clusters - A bunching of data in one region

  4. Graphs for displaying distributions • Boxplot Suitable for: • All types of numerical data • Displaying key features of distributions • Showing skew • Displaying potential outliers (placed as points beyond the whiskers. • Cautions – lacks details and does not show the shape of the distribution well.

  5. Histogram • Suitable for: • Continuous data • Grouped data • Caution: • If bars are too narrow low frequencies hide the shape • If bars are too wide the shape is over simplified

  6. Dot Plots • Suitable for: • Discrete data • Repetitive, rounding, continuous data • Displaying individual counts clearly. • Caution - Not useful when frequencies of individual data are low, or when data is unrounded and continuous. In this case grouping the data in a histogram is better.

  7. Go to Page 141 in Texts • Complete Questions 1, 5, 6 and 7. • Homework – what is standard deviation?

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