Stat 104 Section 5
Josh Zagorsky
<
[email protected]
>
Logistics
1. No section next week
2. Office hours will be shuffled so that all are before the midterm
3.
Midterm exam
67:30pm on Wednesday, March 9th. Last names AM in SC B, NZ in SC C, extended
time students in SC 706. Openbook, opennote, but no laptops allowed.
From PSet #4
1. Bayes’ Rule:
P
(
A

B
) =
P
(
B

A
)
P
(
A
)
P
(
B
)
New Concepts
1. The
Normal Distribution
X
∼
N
(
μ, σ
2
) is a continuous distribution ie. the probability that
x
takes
on any one value is zero; we use it to find the probability that
x
is between
a
and
b
.
A
Zscore
shows how many standard deviations from the mean a value is;
Z
=
X

μ
σ
In Stata, find
P
(
X < x
) by inputting
display normal((x  u)/s)
where
x
is your value,
u
is your mean,
and
s
is your standard deviation.
2.
Sampling:
the sample has mean
¯
X
.
E
(
¯
X
) =
μ
and
V ar
(
¯
X
) =
σ
2
n
.
3.
Confidence Intervals:
you’re some percent confident that the true mean lies within ¯
x
±
t
s
√
n
, where
t
depends on the degrees of freedom (equal to sample size
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 Fall '11
 MichaelParzen
 Normal Distribution, Standard Deviation, Josh Zagorsky

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