Hello,
welcome back to Papers with Backtest podcast.
Today,
we dive into another algo trading research paper.
We are.
And this one looks at something pretty fundamental,
right?
Trading volume.
Exactly.
We're going to unpack the information hidden within unusual trading volume in the stock market based on the study abnormal volume effect in the stock market.
It's a really interesting question,
isn't it?
We tend to focus so much on price,
but what can those big shifts in trading activity actually,
you know,
tell us?
Yeah.
And for you,
if you're thinking about systematic trading,
understanding if these volume spikes are maybe a genuine early warning sign,
well,
that could be a powerful tool.
Definitely.
This specific paper looked at the Italian equity market.
Right.
A specific time frame to 1997 to 2003.
So our goal today,
our mission is to figure out if the significant kind of unexpected jumps in trading volume can give us a peek into future stock price movements.
and crucially,
if there's a way to potentially build actual trading strategies around them.
Okay,
let's dig in.
The paper talks about abnormal volume.
What exactly did that mean in their analysis?
How did they define it?
Well,
they had a very specific definition.
They weren't just looking at high volume days in general.
Instead,
they defined abnormal as trading volume that deviated significantly.
The threshold was more than 2.33 standard deviations from a stock's average trading volume.
over the previous 66 trading days.
66 days.
Okay,
so quite a look back period.
Yeah,
roughly three months of trading.
Think of it like this.
We're not just looking for generally busy days,
but for days where the trading activity is just so far outside the norm for that specific stock.
Right,
suggesting something unusual might be happening.
Exactly.
So it's about a real change in the usual pattern,
not just consistently high activity.
That makes sense.
It does.
Because a stock that always trades heavily
Having another high volume day.
Well,
maybe that's not news.
But a quiet stock suddenly seeing a huge spike,
that's different.
That's when your ears perk up,
yeah.
And they use a specific metric,
normalized abnormal volume,
NAV,
to measure this.
NAV.
Okay,
and that helped compare across different stocks.
Precisely.
It let them compare the unusualness of volume spikes across different companies.
Even if one normally trades millions of shares and another only,
you know,
a few thousand,
it standardized the deviation.
Got it.
And what's fascinating here is that by focusing on these really significant deviations,
the study aimed to isolate trading activity that was likely driven by some sort of new information.
OK,
so they pinpointed these moments of abnormal volume using NAV.
What did they discover then?
How did stock prices behave around these events?
Well,
the core finding was quite remarkable,
actually.
They observed strong positive excess returns clustered around these days of extreme trading volumes.
Strong positive returns.
Yeah.
When the NAV went over that 2.33 standard deviation mark,
they saw an average abnormal return of 2.48%
on the very day of the abnormal volume.
2.48%.
That's significant.
It is.
And an additional
1.02% the following day.
Wow.
And these are excess returns,
right?
Mark and Justin.
Exactly.
Above and beyond what the overall stock market did on those days.
So it's genuine outperformance.
So what did they think was driving this?
Was it simply,
you know,
the mechanics of lots of trading pushing the price up temporarily?
That's a logical first thought.
Yeah.
And the researchers did consider if increased liquidity was the main factor.
But they noted that prices didn't tend to fall back or reverse in the days immediately after the abnormal volume.
Ah,
OK.
No quick reversal.
Right.
That lack of immediate reversal suggested it wasn't just temporary price pressure from the trading itself.
So what else could it be?
They lean towards the idea of price momentum.
You know,
the tendency for prices to keep moving in their current direction,
at least in the short run.
OK,
momentum.
Which suggests that the abnormal volume might indeed be acting as a signal,
a signal of some underlying information pushing the price,
perhaps information that hasn't become public yet.
Now,
that's the interesting part for anyone looking for an edge,
right?
Undisclosed information.
Exactly.
So naturally,
they dug into that.
They looked at whether these volume spikes were just happening when major news announcements hit the market.
Which you'd expect,
wouldn't you?
News breaks,
volume spikes.
You would.
And yeah,
the study did confirm some abnormal volume events did coincide with news releases.
No surprise there.
And what happened then with news?
Pretty much what you'd expect.
Positive news,
generally positive market reaction.
Negative news,
negative reaction.
Okay.
Interestingly,
they also found some signs of underreaction,
especially to bad news.
Prices sometimes continue to drift down even after the negative announcement.
Price continuation even with news.
Yeah.
But here's the key thing,
the really crucial takeaway.
Go on.
The majority of these abnormal volume events,
the larger portion,
did not coincide with any major news being released at the same time.
Really?
The majority?
Yes.
So these were unexplained volume surges.
And they still observe those significant excess returns around them.
Wow.
OK,
that's big.
That strongly suggests the volume itself carries information,
doesn't it?
Even without a public news catalyst.
That's the interpretation.
Yeah.
It opens up the possibility that,
you know,
informed traders might be acting on non-public information and their trading is what's causing these volume patterns.
OK,
so if it's not always news,
maybe it relates to the type of company involved.
Did they look into whether certain firm characteristics made a difference?
They did.
They investigated if features of the company influenced this relationship between abnormal volume and the excess returns.
What popped out?
Ownership and control seemed quite relevant.
For instance,
higher levels of control by the ultimate shareholder were linked to larger excess returns,
both positive and negative,
around these abnormal volume events.
So concentrated control amplified the effect.
It appears so.
And family-controlled firms,
they showed a more pronounced negative price drop when abnormal volumes seemed linked to negative information.
Interesting.
What about things like pyramidal structures or non-voting shares,
ways to separate ownership from control?
Yeah,
they looked at that too,
but the results there weren't as clear-cut.
They didn't find a statistically significant effect for that separation,
at least in this dataset.
Okay.
Any other company features that mattered,
like size or valuation?
Yes.
Smaller firms tended to show larger excess returns around these events.
That kind of makes sense.
Maybe information has a bigger impact there.
Possibly,
yeah.
Also,
firms with higher market-to-book ratios,
sort of growth stocks,
you might say they also exhibited larger excess returns.
Okay.
And liquidity.
Less liquid stocks showed a stronger price impact from abnormal volume.
Again,
perhaps intuitive,
a big surge in trading might move the needle more if the stock doesn't usually trade much.
Right.
Anything else?
Just one more they highlighted.
Higher dividend yield was actually negatively associated with these excess returns,
though they caution that might be partly due to industry effects,
you know,
certain types of companies paying higher dividends.
Got it.
So company characteristics definitely seem to play a role in how informative these volume spikes are.
Seems that way,
yes.
OK,
so let's get to the practical side.
For you listening,
thinking about trading,
did the paper actually test?
If you could create a profitable strategy from this,
what did the backtesting show?
They did explore that,
yeah.
They looked at a pretty basic trading strategy concept.
How did it work?
It was quite intuitive,
actually.
You see a day with abnormal volume,
right,
using that NAV 2.33 signal.
Okay.
Then you look at the price movement on that same day,
the event day.
And use that as a direction signal.
Exactly.
The hypothetical strategy was,
by the next day,
if the price had increased on the abnormal volume day,
and sell or go short,
the price had decreased on that abnormal volume day.
Okay,
makes logical sense.
You're trying to ride that momentum,
assuming the event day price move reflected the direction of the hidden information.
So did it work in the back test?
The results gave some interesting insights,
but also a healthy dose of reality.
Uh-oh,
how so?
First,
they tested a really simple strategy.
Just buy after any abnormal volume spike,
regardless of the price move that day.
Just based on volume alone?
Yeah.
And that long-only strategy actually showed negative returns once they factored in estimated bid-ask spreads.
Ouch.
So transaction costs killed it.
Pretty much.
Just seeing a volume spike on its own wasn't a reliable buy signal once you account for the cost of trading.
At least not here.
Okay,
so that simple approach is out.
What about the one incorporating the price direction?
Buy after a positive day,
short after a negative day.
Right.
When they tested that,
things looked a bit different.
For the long positions buying after a positive return on the abnormal volume day,
they did observe some profitability.
Even after transaction costs?
Yes,
even after accounting for those estimated bid-ask spreads.
And this potential profitability was more noticeable when they focused on larger price movements on that event day.
They looked specifically at thresholds like a 3%
or even a 5%
price increase on the abnormal volume day.
So abnormal volume plus a significant positive price move on that day.
Buying the next day showed some potential edge for longs.
That's what the backtest suggested for this period in marketing,
yes.
Interesting.
What about the other side?
Short selling.
Selling after abnormal volume and a negative price move.
Ah,
well,
that's where it didn't pan out so well.
The short selling strategies they tested,
based on that same principle,
they ended up resulting in losses after transaction costs.
Losses even for the short side?
Why might that be?
Could be several reasons.
Short selling often has higher costs.
you know,
borrowing fees and such.
Plus,
there are often more restrictions or risks involved.
Right.
And maybe just market dynamics during that period in Italy,
perhaps an upward bias or specific short-selling rules.
The paper didn't pinpoint one exact reason,
but the result was clear.
Shorting based on the signal lost money after costs in their test.
Right.
Those market specific factors are always lurking,
aren't they?
So while the paper found these really intriguing patterns around abnormal volume.
Yeah,
the information content seems to be there.
But turning it into a consistently profitable real world system,
especially considering both long and short sides,
sounds like it's much tougher because of those unavoidable trading costs.
That's a really crucial point to understand.
Absolutely.
The theoretical signals might look promising on paper.
But the practicalities of actually trading,
especially the costs,
friction,
they can really change the bottom line significantly.
OK,
so let's try and summarize the key practical takeaways then.
For anyone listening who's thinking about trading rules based on this kind of idea,
what should they keep top of mind?
I think the main thing is,
yes,
abnormal trading volume,
especially in this study,
did seem to contain information and precede short term price moves.
OK,
information is there.
And that information seemed clearer or perhaps more actionable when you combine the volume signal with the direction of the price change on that same high volume day.
Right,
the combined signal.
But the profitability of any strategy built purely on this is heavily,
heavily impacted by transaction costs.
Got it.
Costs are key.
Their backtesting suggested maybe some potential for long positions if you focused on significant positive price moves on those abnormal volume days.
But short selling was a no-go after costs.
Correct.
based on their findings.
So it's definitely not some kind of guaranteed path to easy profits.
No magic bullet then?
Definitely not.
But it does highlight that unusual trading activity,
that volume itself can be more than just noise.
It can carry real information that gets reflected,
at least briefly,
in prices.
Yeah,
it adds another dimension to think about when you're analyzing market behavior,
beyond just looking at price charts.
Precisely.
It underscores that idea that volume isn't just a consequence of trading.
Sometimes it might be an important signal in its own right.
Great insights.
A lot to think about there regarding volume and potential signals.
Definitely food for thought.
Thank you for tuning in to Papers with Backtest podcast.
We hope today's episode gave you useful insights.
Join us next time as we break down more research.
And for more papers and backtests,
find us at https.paperswithbacktest.com.
Happy trading.