Formula Sheet for Exam #2
POS 3713  Spring 2007 (Dr. Hensel)
Note about notation:
X
on this sheet is the same as Xbar in lecture notes
Descriptive Statistics
Proportion: p = f / N
(where f=frequency of cases in this category, and N=total sample size)
Percentage (%) = (f/N)*100
Ratio = f1 / f2
(where f1 and f2 are the frequency of cases in each category)
Rate = actual / possible
(often multiplied by 100, 1000, etc. to help interpret)
Percentage change = ([f2f1] / f1)*100
(where f1=the earlier value and f2=the later value)
Mean:
X
=
"
X
i
N
(where X
i
refers to the individual observations and N=sample size)
IQV =
k
(
N
2
" #
f
2
)
N
2
(
k
"
1)
(where k = # categories, f
2
= sum of frequencies squared, N=sample size)
Deviation =
X
i
"
X
Sum of Squares/Sum of Squared Deviations =
"
(
X
i
#
X
)
2
Variance:
!
2
= SSD/N =
"
(
X
i
#
X
)
2
N
Standard deviation:
!
=
"
2
Std error of mean = std dev of sampling dist. =
"
N
(where
!
=std dev of pop, N=sample size)
Zscores
Z =
X
i
"
X
s
(where X
i
=score,
X
=variable mean, s=variable std dev)
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 Fall '11
 PaulHensel
 Statistics, Normal Distribution, Standard Deviation, std dev, Dr. Hensel

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