R help - Nov 2015 - variance of repeated measurements

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="")
}

I think your imprecise use of statistical methods is getting you into trouble. A
literal interpretation of your question would lead to var(my.data$fluo), but
whether that number would be meaningful would depend on what you did with it (I
doubt much good would come from using it directly). Unfortunately such concerns
are off-topic here (consider discussing at stats.stackexchange.com).
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On November 16, 2015 9:10:29 AM PST, Luigi Marongiu <marongiu.luigi at
gmail.com> wrote:
>Dear all,
>how can I calculate the global variance of repeated measurements? can
>I simply use the var() function or shall i use more sophisticated
>tools such as aov()? and in the latter case, how can i extract the
>variance value?
>I am providing an example.
>Thank you.
>best regards
>luigi
>
>>>>
>samp <- c(1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4,
>          5, 5, 5, 5, 5)
>clock <- rep(1:5,5)
>targ <- c(rep("A", 5), rep("B", 5),
rep("A", 5), rep("A", 5), rep("B",
>5))
>fluo <- c(-0.012, -0.01, -0.008, -0.002, -0.001, -0.007, -0.008,
>  -0.009, -0.009, -0.012, -0.002, -0.003, -0.003, 0.001, 0.002, -0.006,
>   -0.001, 0.001, 0.002, 0.002, -0.002, -0.003, -0.003, -0.002, -0.001)
>my.data <- data.frame(samp, clock, targ, fluo, stringsAsFactors
>FALSE)
>
># variance individual measurement
>sub <- subset(my.data, samp == 1)
>plot(sub$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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