There are about 50–60 brokers with access to the ASX. When I...

There are about 50–60 brokers with access to the ASX. When I refer to "investment banks," I mean a specific group of seven brokers: Citigroup, Goldman Sachs, Macquarie, Merrill Lynch, J.P. Morgan, Morgan Stanley, and UBS. Despite being a small group, they account for a large portion of trading volume. In my tool for broker data, I’ve grouped them together because I prefer to analyze their collective behavior.

Similarly, for retail brokers, I focus on four key players: CommSec, AIEX, CMC Markets, and Wealthhub.

To answer your question — "Where does the rest of the buying come from?" — it comes from other brokers, who are mostly professional investors but belong to different segments. It’s harder to classify them consistently.Personally, I rarely find value in analyzing individual broker activity, which is why I group them. That said, CommSec is an exception and worth analyzing separately since it accounts for 70–80% of retail trading.

You might ask: If retail investors bought 1 million shares from investment banks and the rest went to other professional investors, is that necessarily bad? Maybe not — it depends. It's hard to draw conclusions from absolute numbers alone because participation varies widely by company. For one stock, retail might represent 1% of the trading; for another, it could be 50%.

That’s why I prefer to analyze relative dynamics. For example, observing how retail investors have pivoted from accumulation to distribution (buying to selling) — it’s not about the volume itself, but about the trend.

Another example: as I showed recently, retail investors began buying at a faster pace than before, which usually signals that professional investors are selling more aggressively.