There is no correlation between trade size and price movement.
You nailed the point. After 3 days of loosing money using order book I have learnt the same... But not exactly... There is of course corelation otherwise markets will be just a big mess..
What lessons I've got is - the are 1/10 of data 'big guys' let out.
In first place IB is not an option to trade by book (I dont know why people recommended them so much - may be the others are worse). But with 5 levels of price and no IDs of bidder/sellers - it is not very far from trading CFDs with IG.
In second place there are (as the other people mentioned) MM voluntarily movements (when they can increase they poistion and get filled in microseconds that you wont be able to understand what have just happened - only prints will show. But your stop is already hit!
Also there are number of inconsiderate traders (thank you to online brokers and arcades) who uses techniques other than yours so they may trade suddenly at bid/ask for reason known to them only and again - price moves and you feel tricked as all your 'order book indicators' told you opposite direction.
So there is correlation. Unfortunately we dont have access to enough information (in quantity and quality) to make trades more than just chart woodoo and zen-buddihsm.
Everything is simple like E=mc2 but if you could get that pure E then 1kg of sh@tz can produce energy for whole Earth population for 1000 years!
We have billions tonns of sh@tz but energy resources are getting more and more in scarce (ask Oil traders
).
But I havent given up ! yet