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Chapter 1: The Normal
Distribution
AP Statistics Standards
I. Exploring Data: (continued).
II. Anticipating Patterns:
C. The normal distribution
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Properties of the normal
distribution
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Using tables of the normal
distribution
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The normal distribution as a
model for measurements
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Objectives |
| Essential Question:
Is the bell-curve real? |
The Normal Distribution
- Define density curve.
- Models a distribution
- Above horizontal axis
- Area under it = 1
- Area under part of the curve = probability
- Describe the normal distribution.
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Symmetrical
- Bell Shaped
- Range negative infinity to positive
infinity
- State where the 2 inflection points
fall on a normal distribution. This will help you draw the norm. distr.
(± 1 sigma from the mean)
- State the probability of getting a data point with a
specific value. zero. Why? A point has a width of
zero, hence, here's zero area under a
single point on the normal distribution
- Correctly use N (mean, sigma) notation.
- State the effects on a
normal distribution
of increasing standard deviation.
Relevance: The normal distribution is
ubiquitous. Discussions about it pop up in all kinds of both technical, news,
and popular publications.
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Activities |
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- Lesson 1
- Key Concept: What is a normal distribution?
- Purpose: Lay the foundation for using the normal
distribution.
Interactive Discussion:
Objectives.
- Explain why the
68-95-99.7 Rule is
critical for developing "normal distribution intuition".
- Explain the terms concaved
downward, concaved upward.
- Using a piece of string,
demonstrate the effects of changing the standard deviation

Normal Distribution, Wikipedia,
http://en.wikipedia.org/wiki/Normal_distribution, 9-8-2008
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| Essential Question:
How is the area under the
bell-curve related to the standard deviation? |
Estimating Areas Under Normal
Distributions
- Find probabilities (areas under the curve)
using the
68-95-99.7 Rule
for normal distributions
(sometimes called the empirical rule).
Note:
in the 1st part of the test for this chapter, you will not be permitted to use calculators or
tables. The entire test will be based on the above rule.
Relevance: If you know the empirical rule you
can easily double check your answers when solving for areas under the
n-distribution. The ability to evaluate answers is a very high level skill.
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- Lesson
2
- Key Concept:
Estimating areas under the normal distribution?
- Purpose: Lay the foundation for using the normal
distribution.
Interactive Discussion:
Objectives. Explain why the
68-95-99.7 Rule is
critical for developing "normal distribution intuition".
Group Work:
Use the small white boards to record
the work and the empirical
rule to:
- Find
various areas under the n-distribution using problems directly
related to the empirical rule.
- Find areas using the empirical rule to
estimate areas when the limits on the areas don't perfectly
correspond to the values in the empirical rule.
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| Essential Question:
Does an ogive give the
same information as a normal distribution? |
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Convert the N-distribution into an ogive (cumulative
frequency plot) using the empirical rule.
- Estimate the mean, median, sigma, Q1, Q3, and IQR using an
ogive for a normal
distribution.
Homefun: prob. 2.11, 2.13,
2.15
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- Lesson
3
- Key Concept:
The empirical rule and normal distribution can be expressed in
ogive form?
- Purpose: Lay the foundation for using the normal
distribution.
Interactive Discussion:
Objectives. Explain why the
68-95-99.7 Rule is
critical for developing "normal distribution intuition".
Group Work:
Use the small white boards to record
the work and the empirical
rule to:
- find various areas under the n-distribution.
- create an
ogive

Normal Distribution, Wikipedia,
http://en.wikipedia.org/wiki/Normal_distribution, 9-8-2008 |
| Essential Question:
How is the area under a
non-bell-curve related to standard deviation, median and mean? |
- Describe how the median and mean are related to the area
under the curve for any density curve (p.82).
- Median:
the equal area point
- Mean: the balance point
(directly under the center of mass if the distribution were cut out
of a piece of plywood)
- Estimate the median, quartiles, and probabilities for any
distribution by estimating the area under the curve:
- Be as one with the
0-75-89 Rule based on Chebyshev's Theorem,
which applies to any distribution.
Note: this is the worst case situation for any distr. It gives an
indication of how big the error would be in calculating areas if a
distribution is incorrectly identified as a normal distribution.
- Chebyshev's Theorem:
- p = (1 - 1/k2)
Where: p = the lowest possible
probability of finding a value between ±k
standard deviations from the mean.
Homefun: prob. 2.3, 2.7, 2.9
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- Lesson 4
- Key Concept:
Characteristics of "non-normal" distributions
- Purpose:
To relate areas under a non-normal distributions to measures of
central tendency and spread.
Interactive Discussion:
Objectives. Use Chebyshev's Rule rule to
help understand the power and limitations of the empirical
rule.
Group Work:
Estimate mean, median, quartiles,
and probabilities using the following distributions:
- uniform
- triangular
- skewed
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| Essential Question:
How can the area under the bell-curve
be determined more accurately than by estimating? |
Calculating Areas Under the Normal
Distribution
- Calculate z-scores.
- z = number of standard
deviations from the mean
- Find areas under the normal distribution using
tables. Note, the tables contain a "standardized normal distribution".
Here, the mean = zero and the standard
deviation = 1.
Probability = area under curve
- Find
z-scores corresponding to LL, Q1, median, Q3, UL of a modified box and whiskers plot
for normally
distributed data.
- Using a normal distribution, estimate a critical
value given the probability of finding a value as extreme or more extreme
(a
tail area).

Homefun: prob. 2.21, 2.23,
2.25
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- Lesson 5
- Key Concept: Area under
the normal distribution and how it relates to a box and whiskers
plot.
- Purpose: Understand when
a data set is normally distributed.
Interactive Discussion:
Objectives
2-person teams: Derive an
equation for the z-score
Seat Work: Find the area under n-distribution using tables
and the TI-83 calculator.
2-person teams:
- Derive the z-scores of Q1, Q2,
LL, UL
- Draw a box and whiskers diagram
of an n-distribution
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How to Calculate the Normal
Distribution
pdf = 1/[σ(2π)] • exp[ - (x -
μ)2 / (2σ2)]
- Where:
- pdf = probability density function (height or y-axis coordinate of the N-distribution)
- x = horizontal
axis coordinate
- μ =
mean
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σ = the standard deviation
Note: determining the shape of the normal
distribution requires a knowledge of both the mean and
standard deviations
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| Essential Question:
How can we tell if a
distribution is normal and why would we care? |
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Judge the normality of a distribution by
examining histograms, stem plots, dot plots, ogives, or box and whiskers plots.
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Bell shaped
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Sym-metrical |
Follows 68-95-99.7 Rule |
whisker ≈ 1.5 x ( box width) |
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histograms, stem plots, dot plots |
x |
x |
x |
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ogives |
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x |
x |
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box & whiskers plots. |
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x |
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x |
- Judge the normality of a distribution
using a normal quantile plot on a TI-83.
n-distributions look like straight lines on normal quantile plots.
| Essential Question:
What is the best way to
find probabilities associated with normal distributions? |
- Work quality control reject rate problems.
Note: rejects occur in the tail areas.
- Find areas under the normal distribution using tables
using a TI -83 calculator.
normalcdf (L,U,M,S)
Have you taken your LUMS today?
- Lower
value
- Upper
value
- Mean
- Standard
deviation
- Given a tail area, find the critical value (see
objective 15) using a TI-83 calculator.
invNorm (A,M,S)
I think therefore I AMS.
- Area
(must be a decimal fraction)
- Mean
- Standard
deviation
Remember, in tables for
finding standard normal distribution probabilities, the mean = zero and
the standard deviation = 1. If these values are input into
invNorm along with an area,
the result will be a z-score.
Homefun: prob. 2.27
| Essential Question:
How can I make an "A" on
the test? |
Normal Distributions Review
- Work the practice test.
- Review the objectives.
- Look over
free response problems
from previous years.
- Master the vocabulary (see example
below).
Summative Assessment:
Test--Objectives 1-20
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- Lesson 6
- Key Concept: Determining
normality.
- Purpose: Understand when
a data set is normally distributed.
Interactive Discussion:
Objectives
Seat Work: evaluate whether
various data sets are normally distributed by using the TI-83 calculator.
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