Richard Russell, editor of Dow Theory Letters, is the lone bear of these three. After Thursday's trading session, he wrote: "Today the Dow [Industrials] and the [Dow] Transports both closed below their January lows. Now we have what I would call a Dow Theory bear signal in that both Averages have etched out definite downward zig-zag formations."

Why don't the other two Dow Theorists I monitor agree with Russell's interpretation? A little background is helpful to understand their position.

In very general terms, here are the three preconditions that must be met in order for a Dow Theory sell signal to be generated:

• First: From joint new highs in both the industrials and transports averages, the market must experience a significant correction.
• Second: In the subsequent rally off of the lows set in that correction, either one or both of these two averages must fail to surpass their previous highs.
• Third: Following this failure, both averages must proceed to break below the lows set in the first step's correction.

According to Richard Moroney, editor of Dow Theory Forecasts, we have yet to make it beyond the first of these three steps. After all, we don't yet know whether the correction that began following the averages' early March highs is over. Only when it has, according to Moroney, will we be able to proceed to the next step and focus on the averages' rallies off those lows.

So reports of a Dow Theory sell signal are premature at best, according to Moroney. It will be several more months at a minimum before such a sell signal would become even possible.

In the meantime, Moroney remains bullish, since that the last signal generated by the system was a "buy."

Jack Schannep, editor of TheDowTheory.com, agrees with Moroney's interpretation. In order for a sell signal to be generated, Schannep wrote after Thursday's close, "it would require a 'failed' bounce after this pullback and then new lows."

Until and unless that happens, he also believes that the Dow Theory is bullish.

Unfortunately, the Hulbert Financial Digest's track records for these three newsletters provide little assistance in deciding which of them are more worthy of our attention. Though the HFD has been tracking Schannep's record for just a couple of years, it has performance data for the other two Dow Theory services dating back to 1980, some 25 years ago -- and their records are broadly similar.

Consider first a portfolio that used Dow Theory Forecasts' timing advice to invest either in the Wilshire 5000 index or 90-day T-Bills. From mid-1980 through this past March 31, this portfolio produced a 12.1 percent annualized return, according to the Hulbert Financial Digest.

To be sure, that's 1.7 percentage points per year ahead of the return of a portfolio that instead relied on Dow Theory Letters' timing advice over this period.

However, because the Dow Theory Letter's portfolio was significantly less risky than Dow Theory Forecasts', its performance on a risk-adjusted basis is just as good (and, in fact, is slightly better).