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This would produce a more-or-less systematic difference. But I have noticed
two different anomalies: (1) a small very short-term (a few minutes) random
fluctuation over the course of a day, and
(2) a situation where the two feeds were nearly identical on most days, but
with occasional days when the sum of advances and declines was nearly
identical but the difference (advances minus declines) differed between the
two feeds by between 50 and 100. Furthermore, this interfeed difference
remained virtually constant throughout the entire day, but the next day all
was well again.
Case #1 is to be expected. Case #2 is very strange - it is as if one of the
feeds has transposed a set of particular issues from the adv category to the
decl category (or vice versa) and retains that transposition all day.
Carroll Slemaker
> Advance Decline statistics differ among the various providers due to the
> definitions that vary among them.
>
> Many publish the gross advance declines (including all of the securities
traded
> on the exchange, regardless of type) and others remove the advance decline
> numbers the issues which are not strictly pure individual equities, i.e..
> preferreds, etc., on the assumption that changes due to interest rates
and/or
> other factors are not indicative of equity changes.
>
> Richard Funkhouser
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