Research Methods: 2 M.Sc. Physiotherapy/Podiatry/Pain

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Research Methods 2M.Sc. Physiotherapy/Podiatry/P
ain

• Frequency/Probability Polygons, and the Normal
  Distribution

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Part one Frequency Tables

• Un-grouped
• Tally observations
• Frequency table
• Histogram
• Polygon

• Grouped
• Set class limits
• Tally number in class
• Frequency table
• Histogram
• Polygon

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Ungrouped Frequency Tables Data from n 25,
rating 1-5 of RM2 teaching
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Ungrouped Frequency Tables Frequency Table
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Ungrouped Frequency Tables Data from n 25,
rating 1-5 of RM2 teaching
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Grouped Frequency TablesData of weights (kg) n
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Grouped Frequency TablesSetting class limits

• Find range
• Choose number of classes (5 lt gt20)
• Classes equal size (Outliers?)
• Choose limits at level of measurement precision
• Tally

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Grouped Frequency Tables

• Class boundaries
• Half way between classes
• One more decimal place than limits
• Class intervals
• Distance between boundaries
• Midpoints
• Half way between boundaries
• Mid point of interval

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Grouped Frequency Tables
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Grouped Frequency Tables
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Histograms

• Present information from Frequency tables
• Show distribution of the data set
• Columns start and end at class boundaries
• Midpoints are marked
• Join midpoints Frequency/Probability Polygon
• Area represent frequency/ probability total area
  under curve p 1.00

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Histograms Frequency
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Histograms Probability
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Frequency/Probability Polygons
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Part two The Normal Distribution

• A type of (family) of distributions
• Most important of all known distributions
• Natural parameters in populations
• Symmetrical bell shaped curve

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Normal Distribution
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p if not exact multiple of SD away from mean ?
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Z scores

• Data point of interest x
• Mean ?
• Standard deviation ?
• Z score is number of multiples of SD the data
  point is away from mean
• z x - ?
• ?

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Z scores

• Look up the Z score in Tables to find
• Probability associated with values below x and
  vice versa.
• Why ???

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Graph of number of visits to Physiotherapist for
Sports rehabilitation
z (16 - 10) /4 z 1.5
? p 0.9332 ? p 1 - 0.9332 ? p 0.067
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