Chapter 7 – The Normal Curve
I.
The Normal Curve
a.
In essence is a graphic picture the bellshaped normal distribution.
b.
Normal distribution: The graph shows most of the scores clustered in the
middle around the mean/median/mode, with all the other frequency
distributions on either side gradually lessening.
II.
Characteristics of the Normal Curve
a.
The curve is bellshaped and symmetrical.
b.
The mean, median, and mode are all equal.
c.
The highest frequency is in the middle of the curve
d.
The frequency gradually tapers off as the scores approach the ends of the
curve.
e.
The curve approaches, but never meets the abscissa at both the high and low
ends.
i.
Normal curves are used to describe populations and must be open ended to
allow for the rare scores that do not fall within three standard deviation
units of the mean.
f.
One standard deviation unit is also equal to a z score of 1.
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i.
Ex: When the mean is 100 and S = 16, one standard deviation unit equals
16 points. Thus, one standard deviation above the mean would be equal to
the mean PLUS (1 x 16) which is 116, and two standard deviation units
below the mean would equal the mean MINUS (2 x 16) which is 68.
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 Spring '10
 Professor
 Normal Distribution, Standard Deviation

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