Reviewed Practice Problems - no questions 

    Measures of Variability

• Range
• Simplest measure… quick estimate
• Most subject to change
• Only takes into account 2 scores

• Interquartile Range
• IQR = Q₃ – Q₁  or  P₇₅ – P₂₅
• more stable
• appropriate for ordinal or skewed data
• considers middle 50% of the distribution

• Standard Deviation and Variance
• most stable
• best for interval and ratio data

• Variance
• Takes into account the distance that each score is from the mean
• The average squared deviation from the mean
• Square-root of variance is the standard deviation (SD)
• SD can be thought of as the average deviation - the average amount each score deviates from the mean

• Explanation of the concept of variance and standard deviation using 3 scores (61", 63" and 71")

• Reviewed concept of variance (area) versus standard deviation (linear)

• Example calculation using defination formula and raw score formulas:

        15    15    13    12    10    9    9    8    7    2

variance = 14.20
standard deviation =3.77

• Population vs. Sample Standard Deviation
• sigma  = population
• YOU need to check with your calculator

• SD = sample
• Includes correction factor (n-1 in denominator)
• see formulae on p. 69 in your textbook
  

Homework #2 due Friday (go to Practice/Homework problem link)

Other practice for Monday
    If you have time, work on problems #1-3 on pp. 71-72.
    (for sample SD value, use formulae 5.07 on p. 9)

REMINDER
First Exam - Next Wednesday, February 15th  - Chapters 1-5

Be reading Chapter 5 in textbook.
Based on: Vincent, W. J. (2005). Statistics in kinesiology (3rd ed.). Champaign, IL: Human Kinetics.

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