# Histograms by dfhdhdhdhjr

VIEWS: 4 PAGES: 12

• pg 1
```									              Histograms
A histogram breaks the range of values of a
variable into intervals and displays only
the count or percent of the observations
that fall into each interval.
A person can choose the number of
intervals, but they should be equal length
How to make a Histogram
1. Divide the range of the data into classes
of equal width
2. Count the number of observations in
each class (called a frequency table)
3. Draw the histogram
Large sets of data are often reported in the
form of a frequency table like a histogram
for practicality.
Relative Frequencies are the percentage of
the observation rather than the raw
number.
It is okay to refer to the count and
percentage rather than frequency and
relative frequency.
Since rounding occurs in relative
frequencies there will be roundoff errors.
If too little classes are used in a histogram,
the histogram will have a “skyscraper”
effect.
If too many classes are used in a histogram,
the histogram will have a “pancake” effect.
Looking at data
Outliers have their purpose. A high outlier in
the distribution of brightness scene from a
surveillance satellite may be a missile
launch. A low outlier in a machine-graded
test may point to a student who misread
the question…
Or the student could be an idiot
When outliers are unwanted, search for a
cause of the error. It could be a recording
error, mistyped information, machine
malfunction, etc.
When this is the case, the outlier can be
removed.
Even so, it is risky to remove extraordinary
outliers.
Example 1.10
Time Plots
A time series is a measurement of a
variable taken at regular intervals over
time.
The data is shown in the order it is taken.
Seasonal Variation and Trend
• A pattern in a time series that repeats itself
at known regular intervals of time is called
seasonal variation.
• A trend in a time series is a persistent,
long-term rise or fall.
Example 1.11
An index number a percentage based on the
a starting value.