Director at Costco.
No open-market purchases and 29 sales not made under a pre-set plan, reported from January 3, 2019 to January 20, 2026.
What happened after Decker Susan L’s sales?
After their sales, the shares moved +8.1% against the index over 12 months on average (a negative figure means selling was the right call); 29% trailed it.
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
Decker Susan L: 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
29
−0.2%
+2.8%
45%
8
−0.67
0.52
No reliable evidence
Sales, 12 months after the report
28
+8.1%
+10.3%
29%
7
1.33
0.23
No reliable evidence
Sales, 12 months after the trade
28
+6.8%
+8.3%
29%
7
1.13
0.30
No reliable evidence
“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 Decker Susan L traded and do not suggest the use of non-public information.
How every insider compares · the insider trading backtest.
