Unfortunately, the answer is:  it depends.  Specifically, it depends on
__what__ you want to represent in your summary.  You need to decide
that before we can talk about "how".  It is unclear whether you are
looking for help on "how" so much as you might be asking for
suggestions on "what".

In your original posting, you asked about AVERAGE v. summing and
dividing by 12.  I noted that the results should be the same.  But your
leading question implied to me that you want to represent "typical"
statistics "per month"; for example, the "typical" minimum, maximum,
average and standard deviation.

That is not an unreasonable way to summarize your results, although you
need to be careful about it.  For example, while you might talk
separately about the "typical monthly average" and the "typical monthly
minimum", it would be wrong to talk about the "typical monthly average
__with__ a typical minimum".  In other words, it would be wrong to
assume that the "typical" statistics coincide or work in tandem.

But now you write:

That suggests to me that perhaps you want to represent statistics for
the total year, combining the monthly data.  For example, if the
monthly statistics represent the daily average or the average per month
of 60 categories, perhaps you want to represent the daily average or
the average per year of 60 categories.

In that case, you could compute MIN(C2:N2) and MAX(C3:N3), just as you
computed SUM(C1:N1).  However, in general AVERAGE(C4:N4) is not the
same as the average of all the data, unless the divisor (number of days
or number of categories, for example) is the same for each month.
Moreover, there is no meaningful way to compute an annual STDEV from
the 12 monthly STDEV values (C5:N5).  (And I reiterate:  you might want
STDEVP, not STDEV.)

A more reliable way to compute the annual average (i.e. it does not
rely on the same monthly divisor) would be to carry forward N for each
month (C8:N8) and compute SUM(C8:N8) in M8.  N is the divisor used to
compute each monthly average (e.g. number of days or number of
categories).  Then the annual average in M4 can be computed by either
of the following:

=SUMPRODUCT(C4:N4,C8:N8) / M8

=M1 / M8

I would opt for the latter, since you already carried forward the
monthly sums, and you will need them for another purpose, as you will
see below.

To compute the annual std dev, I would also carry forward SUMX2 for
each month (C9:N9) and compute SUM(C9:N9) in M9.  SUMX2 is the sum of
the square of each of the data for each month, for example
=SUMPRODUCT(W5:W64,W5:W64).  Then the annual STDEV (sample std dev) can
be computed in M5 by:

=SQRT( ( M9 - (M1^2 / M8) ) / (M8 - 1) )

Alternatively, the annual STDEVP (population std dev) can be computed
in M5 by:

=SQRT(M9/M8 - M4^2)

I see no way to summarize these statistics based on the summary data in
C6:N6 and C7:N7.  For "data above the average", you might be able to
construct an array formula, I believe using INDIRECT() to construct
references to the per-month worksheets, if they are cleverly named.
Search these newsgroups for other people's solutions to similar
problems (computations across multiple worksheets).  Similarly for
"data below the average"; but the formula that you have does not make
sense to me, if the average is in W68 in each per-month worksheet.

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