[R] Finding the dominant factor in an unbalanced group

[Sandy Small]

Hi all.
This is perhaps more a statistics question but I'm hoping someone can
help me.

I have a group of patients for whom I'm looking at beat to beat RR
interval changes.
I have plotted the difference between one beat length and the next
against the difference between the previous beat length and the current one.
This gives me a plot with four quadrants: the bottom left corresponding
to successively shorter beats, the top right to succesively longer, the
top left to a shorter followed by a longer beat and the bottom right to
a longer by a shorter.

In theory if successive changes in beat length are random there should
be an approximately equal number of counts in each quadrant of my plot.

I have a dataframe which for each of my patients lists the number of
counts in each quadrant:
(dput data at the end of this mail)

I can determine whether the distribution is balanced or not with a Chi
Squared (chisq.test)

However what I would like to do is determine whether there is a dominant
quadrant (eg. CBP06118 in the example data), or a dominant pair of
quadrants  (eg CBP06036 in the example data) and if so which they are.
If my dataset were only 10 patients it probably wouldn't be a problem
(although I'm not certain what statistical check I could do beyond
re-applying chisquared tests with only the relevant quadrants which
sounds dodgy to me) the problem occurs because my data set is a couple
of orders of magnitude bigger,

Can anyone help?

dput data is:

structure(list(basestudy = structure(1:10, .Label = c("CBP06036",
"CBP06095", "CBP06098", "CBP06100", "CBP06112", "CBP06118", "CBP06127",
"CBP06158", "CBP06163", "CBP06166"), class = "factor"), tl = c(302L,
211L, 347L, 223L, 178L, 230L, 243L, 278L, 391L, 252L), tr = c(99L,
134L, 171L, 210L, 158L, 252L, 89L, 247L, 258L, 168L), br = c(305L,
212L, 346L, 223L, 178L, 231L, 244L, 277L, 388L, 254L), bl = c(142L,
288L, 284L, 191L, 144L, 360L, 147L, 184L, 164L, 186L)), .Names =
c("basestudy",
"tl", "tr", "br", "bl"), row.names = c(NA, 10L), class = "data.frame")

Many thanks

--

Sandy Small
Clinical Physicist
NHS Greater Glasgow and Clyde
and
NHS Forth Valley



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