[Aavso-photometry] Standard deviation calculation

[arne]

Dave Lane wrote:
> arne wrote:
> 
>>
>> There is no simple mechanism that gives you a perfect estimate of the 
>> error.
>> The (K-C) process gets you most of the way there and is one that we might
>> get most observers to use (rather than the very optimistic Poisson error
>> estimate that many use now).  If you want to try something more accurate,
>> then by all means look at the real error equation and see what results
>> you obtain.
> 
> 
> Arne,
> 
> Should one report just one times the SD of the K-C for the time series, 
> or something more pessimistic (eg. 2SDs=95%). I guess what I'm really 
> asking is what is the error estimate supposed to tell the user about the 
> data and is that documented somewhere?
> 
> ... Dave
> 
For photometric observations, the usual guideline is one standard deviation.
There are exceptional circumstances, usually when you are trying to prove
something (optical transient, detection of something faint, etc.) where you
will use two- or three-sigma for reporting errors.  I'm currently reading the
CCD Manual (created before I started at HQ) to correct errors and bring it
up to date; I'll include that error guideline in that manual.
Arne