variation and measure of dispersion

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will never be asked to calculate SD!

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11 Terms

1
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what are the 2 types of variation?

  • continuous variation

  • discrete variation

2
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what is continuous variation and how can it be displayed? give an example:

  • features showing continuous variation can have any value w/in a range

  • most of the time, most individuals are close to the mean and few are found at either extremes - normal distribution

  • traits often regulated by multiple genes and influenced by environment

  • plotted on histogram overlaid w/ a curve

  • e.g. height

<ul><li><p>features showing continuous variation can have any value w/in a range</p></li><li><p>most of the time, most individuals are close to the mean and few are found at either extremes - normal distribution</p></li><li><p>traits often regulated by multiple genes and influenced by environment</p></li><li><p>plotted on histogram overlaid w/ a curve</p></li><li><p>e.g. height</p></li></ul><p></p>
3
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what is a normal distribution?

data points are grouped symmetrically around central mean, resembling a bell shaped curve

<p>data points are grouped symmetrically around central mean, resembling a bell shaped curve </p>
4
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what is discrete/discontinuous variation and how can it be displayed? give an example:

  • features showing discrete variations have distinct categories w/o intermediate values

  • traits often regulated by a single gene and not influenced by environment

  • plotted on bar charts

  • e.g. blood group

<ul><li><p>features showing discrete variations have distinct categories w/o intermediate values</p></li><li><p>traits often regulated by a single gene and not influenced by environment</p></li><li><p>plotted on bar charts </p></li><li><p>e.g. blood group</p></li></ul><p></p>
5
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what is standard deviation?

the spread of data around the mean

6
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when is a difference significant/not significant?

  • SDs don’t overlap = significant

  • SDs overlap = not significant

7
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what does a smaller/larger SD mean in terms of variation?

  • smaller SD = less variation

  • larger SD = more variation

<ul><li><p>smaller SD = less variation</p></li><li><p>larger SD = more variation</p></li></ul><p></p>
8
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what does a smaller/larger SD mean in terms of reliability?

  • smaller = greater reliability (as data has a narrower range and points are more closely grouped around mean)

  • larger = lower reliability (as data has a wider range and points are less closely grouped around mean)

9
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evaluate the use of the range as a measure of dispersion:

  • strength: easier to calculate (than SD)

  • limitation: distorted by extreme values

10
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evaluate the use of SD as a measure of dispersion:

  • strength: not distorted by extreme values

  • limitation: more difficult to calculate (than range)

11
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how can we evaluate SD data?

  • find +ves in data

  • find +ves in method/procedure

  • find -ves in data

  • find -ves in method/procedure