[R] variance of repeated measurements
Luigi Marongiu
marongiu.luigi at gmail.com
Mon Nov 16 18:10:29 CET 2015
Dear all,
how can I calculate the global variance of repeated measurements? can
I simply use the var() function or shall i use more sophisticated
tools such as aov()? and in the latter case, how can i extract the
variance value?
I am providing an example.
Thank you.
best regards
luigi
>>>
samp <- c(1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4,
5, 5, 5, 5, 5)
clock <- rep(1:5,5)
targ <- c(rep("A", 5), rep("B", 5), rep("A", 5), rep("A", 5), rep("B", 5))
fluo <- c(-0.012, -0.01, -0.008, -0.002, -0.001, -0.007, -0.008,
-0.009, -0.009, -0.012, -0.002, -0.003, -0.003, 0.001, 0.002, -0.006,
-0.001, 0.001, 0.002, 0.002, -0.002, -0.003, -0.003, -0.002, -0.001)
my.data <- data.frame(samp, clock, targ, fluo, stringsAsFactors = FALSE)
# variance individual measurement
sub <- subset(my.data, samp == 1)
plot(sub$flu ~ sub$clock)
abline(lm(sub$flu ~ sub$clock))
for (i in 2:nrow(sub)) {
X <- subset(sub, clock <= i)
V <- var(X$fluo)
cat("variance at clock ", i, " = ", V, "\n", sep="")
}
# variance multiple measurements
sub <- subset(my.data, targ == 'A')
plot(sub$flu ~ sub$clock)
abline(lm(sub$flu ~ sub$clock))
for (i in 2:max(sub$clock)) {
X <- subset(sub, clock <= i)
V <- var(X$fluo)
cat("variance at clock ", i, " = ", V, "\n", sep="")
}
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