Psych 100A
Winter 2010
Lecture 3: Descriptive Statistics:
N
i l
i
f d
Numerical summaries of data:
1.Measures of location (cont.)
2.Measures of variation
1

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Calculating median
•
Don’t use the Kiess section called
“calculating the mean with the percentile
f
l ”
h f ll
d
formula”. Use the following procedure
instead.
•
(1) Put all the entries in order from
largest to smallest. If one value is
b
d N ti
th
it h ld
N
observed N times then it should appear N
times in the list. (For example if three
people have score 70 then there are
three 70s in the list). There should be
the same number of items in the list as
there are entries in the original data set.
2

Calculating median (cont.)
•
(2) If the data set contains an odd
number of entries, then the median is the
ddl l f h d
d l
middle value of the ordered list. For
example if we have the list 3, 3, 2, 2, 1,
1 1 The median is the 4th value median
1, 1. The median is the 4th value, median
= 2.
(3) If th d t
t
t i
•
(3) If the data set contains an even
number of entries, the median is halfway
between the two values closest to the
middle of the ordered list. For example if
we have the list 3, 2, 2, 1, 1, 1, then
the median is (2+1)/2 = 1.5.
3

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