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