Histograms by dfhdhdhdhjr

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									              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.
Government agencies often adjust for
 seasonal variation before releasing
 economic data. This is called seasonally
 adjusted.
Other TI-8X Tricks
         Homework pg 23 - 39
•   2, 4, 6, 8, 10
•   12, 14, 16, 18
•   20, 22, 24*, 28
•   34, 36, 39, 40

								
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