Chief executive at Cerus Corp.
4 open-market purchases and 6 sales not made under a pre-set plan, reported from May 4, 2011 to March 14, 2023.
Would copying Greenman William Mariner’s purchases have beaten the S&P 500?
Too few purchases to judge. None of their purchases has 12 months of prices after the report; we judge insiders once they have 20. The figures below can swing a long way on a handful of trades. After their sales, the shares moved −25.6% against the index over 12 months on average (a negative figure means selling was the right call); 75% trailed it. None of their purchases could be priced, so there is no copy portfolio.
With 296 insiders tested, some will look skilled or unskilled by chance alone: when we replaced each insider’s stocks with random companies bought on the same days, about 5.7 cleared the bar ahead and 23.3 behind. One record on its own proves little.
Trade by trade
Greenman William Mariner: trades against the S&P 500 afterwards
Measured
Trades counted
Average vs S&P 500
Median
Went the right way
Years
t-statistic
p-value
Evidence
Purchases, 3 months after the report
0
—
—
—
—
—
—
Not enough years
Purchases, 6 months after the report
0
—
—
—
—
—
—
Not enough years
Purchases, 12 months after the report
0
—
—
—
—
—
—
Not enough years
Purchases, 12 months after the trade
0
—
—
—
—
—
—
Not enough years
Sales, 3 months after the report
4
−3.9%
−4.4%
50%
3
—
—
Not enough years
Sales, 12 months after the report
4
−25.6%
−33.5%
75%
3
—
—
Not enough years
Sales, 12 months after the trade
3
−15.6%
−25.8%
67%
3
—
—
Not enough years
“Average vs S&P 500” is the stock’s return including dividends minus the index’s over the same dates, from the close on the first trading day after the report, or from the close on the trade date.
Only windows that have finished are counted. For sales, a negative figure means the stock lagged after it was sold, so selling was the right call (green).
“Went the right way” is the share of purchases that beat the index, or of sales that trailed it.
The t-statistic uses one average per year of reports, because one person’s trades bunch into the same stock and weeks, and needs trades in at least four different years; the p-value comes from the t distribution with that number of years (with four years, a t of 2 has p = 0.14). “Some evidence” means p under 5%, “strong evidence” p under 1% over at least six years.
Open-market purchases and sales of at least $10,000 in companies we cover, from SEC Form 4 filings; sales made under a pre-set Rule 10b5-1 plan are not shown. “Not yet” means the window has not finished or the share price was under $5 at entry.
These are the shares’ moves after each trade: they say nothing about why Greenman William Mariner traded and do not suggest the use of non-public information.
How every insider compares · the insider trading backtest.
