----- Forwarded by Paul Garcia/Hertford/CSERV/HertsCC on 07/01/2003 11:42
-----
Paul Garcia
To: "Andy Sloggett" <[log in to unmask]>
07/01/2003 11:44 cc:
Subject: Re: Forecast vs Projection - not so.(Document
link: Paul Garcia)
Dear Andy,
My reasoning was thus (using the definitions in my original query, plus an
amalgam of the comments I received):
Take the set of all projections: they are all forecasts, but with no extra
dimensions added. But it is possible to produce forecasts which are not
projections, but based on other stuff (prophecies, gut feeling, etc.). So
the set of forecasts is bigger than the set of projections and includes all
the projections. Ergo: projections are a subset of forecasts.
=========
Best wishes
Paul Garcia
Senior Property Review Officer (Demographics)
25221
=====================================
Hoc fama mihi cursum sinuosum secuta nuntiat
"Andy Sloggett"
<Andy.Sloggett@l To: <[log in to unmask]>,
shtm.ac.uk> <[log in to unmask]>
cc:
07/01/2003 11:22 Subject: Re: Forecast vs Projection - not so.
Paul
Your reasoning that projections are 'purely mathematical ...', whereas
forecasts 'imply extra knowledge ...' is spot on - but then your
interpretation of this seems to be competely contrary.
Forecasts are a subset of projections - not the other way around.
Therefore the phrase 'projections are not forecasts' is certainly true most
of the time, although they can sometimes be the same thing - ie forecasts
are a subset of projections.
One may make many demographic projections - high, median, low variants -
projection of AIDS deaths under various theoretical conditions etc. - but
only one or two of these may be realistic and then, with added judgement
thrown in, they become forecasts.
Projections cannot be wrong, forecasts usually are wrong.
Forecasts involve putting your professional neck on the line, projections
just involve going through the motions. Forecasters are as often wrong as
anybody else but they have to have good and complicated reasons for being
so.
Andy Sloggett
Lecturer in Medical Demography
and MSc Course Organiser
Centre for Population Studies
London School of Hygiene & Tropical Medicine
50 Bedford Square, London, WC1B 3DP
Tel: 020 7299 4628
Fax: 020 7299 4637
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