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1
Review of Chapter 2
s
Range
: one measure of variability
b
Not used to calculate the variance
s
Calculating mean
: (aka “the average”) the
fulcrum around which all the other scores
balance
Review of Chapter 2
s
Calculating the variance:
s
1. find the mean
s
2. subtract the mean from each score
b
This is the deviation score
s
3. Square the deviation score
s
4. Add the squared deviation scores
b
This is the Sums of Squares
s
5. Divide the Sums of Squares by n1
b
“n” = the number of participants
s
**The range is not needed for these calculations
Standard Deviation
s
*Not mentioned in Chapter 2*
s
Standard Deviation
: the square root of the
variance
s
If the mean
and standard deviation
of a normal
distribution
are known
b
it is possible to compute the percentile rank
associated with any given score.
b
In a normal distribution, about 68% of the scores are
within one standard deviation of the mean and about
95% of the scores are within two standards deviations
of the mean
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Calculating Variance and the
Standard Deviation
Mean=5.6
5.6^2=31.36
05.6=5.6
0
5
4.4^2=19.36
105.6=4.4
10
4
3.4^2=11.56
95.6=3.4
9
3
.6^2=.36
55.6=.6
5
2
1.6^2=2.56
45.6=1.6
4
1
Squared Deviation
Deviation Score
Score
Participant
Calculating Variance and the
Standard Deviation
= 65.2
+ 31.36
19.36
11.56
.36
2.56
Sum of
Deviation
score
s
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 Spring '07
 TRCunningham

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