26. Levels of measurement (cont.) Symmetrical – Mean Skewed – Median Addition, subtraction, multiplication and division Ratio Symmetrical – Mean Skewed – Median Addition and subtraction Interval Median Greater or less than operations Ordinal Mode Counting Nominal Best measure of central tendency Permissible mathematic operations Measurement scale
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28. The shape of data (cont.) Line depicting the shape of the data
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30. The normal distribution (cont.) Mean A normal distribution is symmetric about its mean As one moves away from the mean in either direction the height of the curve decreases, approaching, but never reaching zero The highest point of the overlying normal curve is at the mean
51. Spread is important when comparing 2 or more group means It is more difficult to see a clear distinction between groups in the upper example because the spread is wider, even though the means are the same