Diff for "FAQ/perc" - CBU statistics Wiki
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Revision 11 as of 2008-04-11 11:14:32
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Editor: PeterWatson
Comment:
Revision 12 as of 2008-04-11 11:50:52
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Editor: PeterWatson
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Deletions are marked like this. Additions are marked like this.
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perc <- rep(-99,length(score))
a <- rep(-99,length(score))
ict <- 0
b <- duplicated(score)
ict <- ict+1
Line 22: Line 27:
if (b[i] == FALSE) {
ict <- ict+1
a[ict] <- score[ict]
 }
Line 24: Line 33:
a

How do I find out how many people have a score above a certain value?

Percentiles give the percentage of people who have a score below a threshold score.

Percentile (score) = 100 $$\frac{\mbox{n} \leq \mbox{score}}{\mbox{N}}$$

100 - Percentile (score) = 100 $$\frac{\mbox{n} \gt \mbox{score}}{\mbox{N}}$$

The percentiles for each score are routinely outputted using the frequency procedure in SPSS.

FREQUENCIES VAR=SCORE.
EXE.

In R the percentages of people with scores equal or below each observed score can be obtained by running

perc <- rep(-99,length(score))
a <- rep(-99,length(score))
ict <- 0
b <- duplicated(score)
ict <- ict+1
for (i in score) {
perc[i] <- 100*sum(score<=i)/length(score)
if (b[i] == FALSE) {
ict <- ict+1
a[ict] <- score[ict]
 }
 }
perc
a

None: FAQ/perc (last edited 2013-03-08 10:17:13 by localhost)