Quantiles revision

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  • Created on: 21-05-11 14:04
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Quantiles
·
A
quan/le
is
a
sta/s/c
that
measures
a
certain
propor/on
of
the
way
through
a
set
of
data.
They
are
measures
of
spread
(dispersion).
·To
find
different
quan/les
in
a
set
of
data,
use
the
following
method;
Find
the
number
of
items
in
a
set
of
data
(take
this
to
be
n)
Mul/ply
n
by
the
relevant
frac/on
in
the
table.
Quan/le
Example
Frac/on
Quar&les
Q1
(Lower
Quar/le)
¼
Q2
(Median)
½
Q3
(Upper
Quar/le)
¾
Deciles
D1
...
D9
1/
10
e.g.
D3
3/
10
Percen&les
P1
...
P99
1/
100
e.g.
P70
70/
100
CAUTION
for
all
Quan&les
Ø If
the
answer
is
a
WHOLE
NUMBER
then
take
the
mean
of
this
piece
of
data
and
the
next
e.g.
find
the
mean
of
the
7th
and
8th
pieces
of
data.
Ø If
the
answer
is
NOT
A
WHOLE
NUMBER,
ALWAYS
ROUND
UP
e.g.
3.36
è4th
piece
of
data.
·
RANGE
­
Maximum
Value
-
Minimum
Value
·
IQR
(Interquar&le
Range)
­
Q3
-
Q1
·
SIQR
(Semi-Interquar&le
Range)
­
Q3
-
Q1
2

Comments

daviesg

A really good presentation showing different measures (quantiles) which are used in measures of spread, e.g. quartiles, percentiles etc

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