Hi people
I changed the parameters of simpleaffy pairwise filter to:
min.exp=log2(10), min.exp.no=2, fc=log2(2), min.present.no=2, tt=
0.05,
present.by.group=TRUE
The situation didn?t change.
I had only 6 genes differentially expressed in the comparison of two
different groups. Each group has only 3 arrays.
Should I reduce the stringency? What parameter?
For others comparisons I had 50, 200 etc genes. But when I did the
clusterization
everything was red!!!!
Anybody know what happened?
Thanks
Patr?cia
> Hi Patricia
> your paramters are as follows
>
> min.exp - the minimum expression level you would typically expect to
see
> in
> your experiment. For Affymetrix experiments, the default here has
been set
> at log2(10), but that would obviously depend on your experiment and
also
> how
> you have normalised the data
>
> min.exp.no - the minimum number of arrays you want your probeset to
show
> the
> min.exp on. In your experiment, it is set at 2 so you are filtering
> results
> to only show probesets with a minimum expression of log2(10) on at
least
> two
> arrays
>
> min.present.no. - this is the minimum number of arrays a probeset
must be
> called present on to be included in the analysis...in your case you
have
> it
> set at 4.This means you are filtering your results to only include
> probesets
> that are present on at least 4 arrays. Again the number here very
much
> depends on your experiment, the number of groups you have and the
number
> of
> arrays. In a simple experiment comparing 2 conditions using 3 arrays
in
> each
> condition, I would set it at 2 or 3 (so the probeset has to be
called
> present on half of the arrays in your experiment)
>
> present.by.group - this allows you to further specify how your
present
> calls
> are. You have set it at FALSE, so your results are filtered to only
show
> those probesets that are called present on at least 4 arrays in the
whole
> experiment. If you set it to TRUE, then the probeset must be called
> present
> on at least 4 arrays in one of your conditions. Again what you set
it at
> depends on your experiment. In my simple 6 array, 2 condition
experiment I
> would set it to TRUE meaning my results will only include probesets
that
> are
> present on at least 2 arrays in either condition. This allows you to
> account
> for probesets which may be absent in one condition, but present in
another
>
> try typing openVignette() in your R session and selecting
simpleaffy.
>
> hope this helps
>
> claire
>
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>
Patr?cia Luiza Nunes da Costa
Laborat?rio de Oncologia Experimental, Grupo de Ades?o Celular
Faculdade de Medicina da Universidade de Paulo-FM USP
Av. Dr. Arnaldo, 455 sala 4112
Cerqueira Cesar
Cep 01246-903
Tel: (11) 3061-7486 e (11) 8202-7073
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