I think it is determined by how many sectors you want to trade in.
In my case I will generally trade in
Techs..
Broken down into several categories such as semis, software, networking, internet, fibre optic, alternative energy, etc., etc.
Then we have:
Banks
Brokerages
Oil Services
Drugs
Biotechs
Retailers
So right there you have 7 groups, and the techs need to be subdivided into at least another 5 or more subgroups.
There are so many groups. There has to be a limit because of the size of the screen and the size of my brain. I could look at defense, consumer, transportation, metals, homebuilders, and on and on. But I leave that to others. There are just too many. I stick to where the volume is. When it changes, then I will too.
So on my screen, I will have about the 10 or so thickest trading stocks in each group. (More semis than brokerages, and so on). So that becomes better than 120 stocks on my screen. I really have more...but you get the idea.
Now of these, there are a significant number of stocks I have never traded, or that I trade very rarely. Then there are the usual suspects which amount to about 30-40 which I trade frequently. Of those, I do probably 90% of my trades in the same 15-20 stocks. (which change over time) But I like seeing all the stocks because even though I don't trade most of them, I find it helpful to see how the stocks I do trade are doing relative to their group, and how the group is relative to the market.
No such thing as too much information. I have software that scans all the stocks I have ever traded searching out the parameters I put in. Occasionally this will point out some obscure (to me) stock because of exceptionally high volume, or movement, or whatever. This kind of software is commonplace.
Seeing all those stocks at once also gives me a better "feel" for the market.
Oh yeah, I keep some indexes, s&p futures, market and up down voume, tick, trin, and most important, the TIME. That way I have one sure thing .... I know it will go up from 9:30, and is a major short at 12:59 (but you gotta cover right away)
