Hi Richard and Jesse

RR> I'm surprised enough that nobody's answered this, that I think I must

RR> be missing something.

It looks that I din't spot that message until you replied... Sorry

RR> At 03:18 PM 9/28/2006, Jesse Jahrig wrote:

>>Can anyone tell me how to calculate the coefficient of variation using

>>SPSS?

RR> If, as I understand, you mean simply the standard deviation divided by

RR> the mean, then if you want the CV of a single variable across cases,

RR> AGGREGATE using functions MEAN and SD, and divide the results; if it's

RR> multiple variables in one case, use functions MEAN and SD in the

RR> transformation language (in COMPUTE statements), and divide the

RR> results.

My contribution to the topic (better late than never)

If you don't want the CV as a new variable, but simply as a statistic

in a pivot table, you can also use RATIO: this procedure computes

several statistics for the ratio of two variables, including

confidence intervals for the median and coefficient of variation (mean

and median centered). To trick RATIO to compute a cv or a median CI

for a SINGLE variable (not the ratio of two variables) you just have

to compute a variable filled with "1" and use it as denominator. The

result will be the CV for the ratio between your variable and 1, and

it is evident that any variable divided by 1 remains unchanged.

See this example (I have added also the 95%CI for the median, just for

didactic purposes), if you don't want it erase "CIN(95) MEDIAN":

DATA LIST FREE/dietgroup iron (2 F8).

BEGIN DATA

0 83 0 76 0 112 0 113 0 115 0 91 0 101 0 84 0 92 0 73

0 91 0 95 0 107 0 118 0 123 0 96 0 84 0 118 0 122 0 78

0 117 0 103 0 98 0 111 0 130 0 79 0 130 0 126 0 141 0 115

1 75 1 122 1 128 1 88 1 112 1 110 1 106 1 130 1 79 1 131

1 97 1 125 1 102 1 71 1 111 1 132 1 106 1 92 1 108 1 87

1 86 1 87 1 98 1 132 1 94 1 92 1 121 1 86 1 122 1 100

1 108 1 96 1 115 1 114 1 75 1 84 1 98 1 95 1 86 1 78

1 114 1 114 1 101 1 95 1 99 1 96 1 108 1 86 1 97 1 114

END DATA.

VAR LABEL dietgroup 'Diet Group'/

iron 'Seric Iron levels (µg/100 ml) '.

VALUE LABEL dietgroup 0 'Standard' 1 'Vegetarian'.

TEMPORARY.

COMPUTE one=1.

RATIO STATISTICS iron WITH one BY dietgroup

/PRINT = CIN(95) MEDIAN MNCOV .

--

HTH & Regards,

Dr. Marta García-Granero,PhD mailto:

[hidden email]
Statistician

---

"It is unwise to use a statistical procedure whose use one does

not understand. SPSS syntax guide cannot supply this knowledge, and it

is certainly no substitute for the basic understanding of statistics

and statistical thinking that is essential for the wise choice of

methods and the correct interpretation of their results".

(Adapted from WinPepi manual - I'm sure Joe Abrahmson will not mind)