Discussing Samples

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# Discussing Samples - PowerPoint PPT Presentation

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

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)

• 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
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.
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

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.

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