trading sttrategy based on premarket data

Premarket data are useful indicators. When the price of a stock increases in premarket with a good volume (for ex. 5% the average volume) as a consequence of a positive news (earnings higher than expected, a buy advice by an important analyst etc.) often but not always the price increases further after 9.30 am ET. But sometime the price drops with no apparent reason. Perhaps for technical reasons?.
Anyone has an answer? Is it possible to identify those stocks that will increase further and those that will decrease?
This is a difficult question but very important. Thanks!

I use the premarket data to get into the days trading with a position at 8 am every morning. I start utilizing the data starting at 6:15am and get in at 8 based on cumulative bid and cumulative up down bar volume. It usually puts me in the correct direction. Premarket data is really just market data. I can't trade with my platform on ES before 8am but others can. Low volume usually gives the strongest signals as to which direction to go as long as the sentiment follows the direction of price.

Cheers

numbertea said:

I use the premarket data to get into the days trading with a position at 8 am every morning. I start utilizing the data starting at 6:15am and get in at 8 based on cumulative bid and cumulative up down bar volume. It usually puts me in the correct direction. Premarket data is really just market data. I can't trade with my platform on ES before 8am but others can. Low volume usually gives the strongest signals as to which direction to go as long as the sentiment follows the direction of price.

Cheers

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Thank you for your interesting reply. A possible example is July 12 WBMD (Google finance) : due to improved earnings outlook the price increased from 27.0 ( july 11 4pm) to 31.0 (july 12 8 am, + 14.5%) to 32.3 ( 9.28 am, + 19.6%) and 34.5 four minutes later. In this case would you have invested for ex. $ 20.000 and at what time? It seems to me quite risky to enter after a large increase of 14 or 19% . The price can go up further or can go down. The question is: is there a helpful method to make the right decision?