I'm trying to understand what caused certain price movements (aren't we all!) in per-minute data for major NYSE stocks. In particular, I'd like to determine whether a given price movement of X% in either direction was due to a single entity making a large trade (maybe their order-splitting algorithms leave traces, or maybe they skipped that and had to buy/sell in a hurry) versus an aggregation of many small orders.
What is the best way to approach this analysis?