Annual Incomes of 10 Families

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Why do we need the standard deviation? 1- The
standard deviation reflects dispersion of data
values, so that the dispersion of different
distributions may be compared by using standard
deviations. 2- The standard deviation permits
the precise interpretation of data values within
a distributions. 3- The standard deviation, like
the mean, is a member od a mathematical system
which permits its use in more advanced
statistical considerations.
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EMPIRICAL RULES 1- About 68 of the values will
lie within 1 standard deviation of the mean, that
is, between x - s and x s 2- About 95 of
the values will lie within 2 standard deviation
of the mean, that is, between x - 2s and x
2s 3- About 99.7 of the values will lie within
3 standard deviation of the mean, that is,
between x - 3s and x 3s
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BOX PLOT A Box Plot is a graphical summary of
data that is based on five number summary. To
construct a box plot use the following STEPS 1- A
box is drawn with the ends of the box located at
the first (Q1) and third quartile ( Q3) 2- A
vertical line is drawn in the box at the location
of the median. 3- By using IQRQ3-Q1, limits
(also called fences) are located. The limits for
the box plot are Q1 - 1.5IQR and Q3
1.5IQR DATA OUTSIDE THESE LIMITS ARE CONSIDERED
OUTLIERS 4- The dashed lines (also called
whiskers) are drawn from the ends of the box to
the smallest (L) and highest (H) values inside
the limits computed in STEP 3 5- Finally, the
location of each outlier is shown with a symbol