Do a company's shares trail comparable companies over the month and the year after a priced prospectus?
Study 47 · Changed a rule or plan · recorded 10 October 2026 · answer: Yes · full paper with figures
The question
We compare each company's shares with five comparable companies of the same industry and similar trading size, over the month after the sale in returns and over the year after in growth of wealth, and ask whether any shortfall is brief pressure from the new supply or a lasting lag that is larger after the run-up before the sale.
Rules fixed before the result
Fixed in advance: the study would go on only with at least 400 sales by 150 companies and a comparison able to detect a shortfall of 3 percentage points over the month and 0.10 on the logarithmic scale over the year; it could detect 1.7 points and 0.041. A year's range wholly below zero reads as a lasting shortfall, tied to the run-up only if the slope's range is also wholly below zero; a month's alone reads as brief pressure.
Data and method
We rebuilt the earlier study's 2,190 sales by 745 companies. Over the year we compared each company's logarithmic growth of wealth with its comparables' mean: on the logarithmic scale the rare very large rises no longer dominate the average, and a more volatile share grows more slowly, so the gap is also shown with volatility added back. The same companies' ordinary dates had no sale within a year either side, and the power check took its spread from those years.
The answer
Yes. Over the month after the sale, shares trailed their comparable companies by 4.4 percentage points on average (95% range 3.4 to 5.5). Over the year after, on the logarithmic scale, the gap was 0.25 (range 0.19 to 0.31), beyond the 0.08 named in advance, and it was smaller, not larger, where shares had risen more before the sale (slope 0.16, range 0.06 to 0.26). On the same companies' ordinary dates there was no measurable gap: the ranges ran from a 0.7 point shortfall to a 1.7 point gain over the month and from 0.04 below to 0.03 above over the year. With each share's volatility added back the year's gap stayed at 0.24, on the earlier study's scale of returns it was 12 percentage points (range 7 to 17), and the plan expected this answer with low confidence.
Main estimate
-0.248 fraction (95% range -0.308 to -0.194), from 2190 observations
What it changes
By the rule fixed in advance, these sales become a family of events for further study, and the next question is how the year's shortfall splits by kind of sale and by industry and period, before testing whether it grows with the sale's size or the run-up. Because the shortfall was not larger after a rise before the sale, the explanation that managers sell when their shares are dear gains no support here.
What remains uncertain
These sales were studied before: study forty-six found study forty-five's year unreadable because some companies' very large rises before the sale widened its spread; this plan was fixed after that, with no return after a sale seen. The year's gap is in typical wealth, which higher volatility lowers even with equal expected returns; the filings do not say what was sold. The ranges, resampling whole companies, treat same-week sales by different companies, which share market and industry shocks, as independent.
How it was made
Run took 64 minutes; independent code review: approve; the recorded calculation reruns to the same result.
Fingerprints
plan 2612f889aca20d4a3ac064ccefb2809754a044a409f7165c3c18467d13cc00eb result 66566889eab6226828d1441bd383a95c330495b449bd8dabc2486ac17931e848
Exploratory work on development data; not a performance claim.