Surface Carol A: insider trades

Officer at 2 companies we cover. No open-market purchases and 10 sales not made under a pre-set plan, reported from September 22, 2011 to March 14, 2022.

What happened after Surface Carol A’s sales?

After their sales, the shares moved −14.3% against the index over 12 months on average (a negative figure means selling was the right call); 80% 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

Surface Carol A: 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	10	+5.3%	−0.9%	50%	8	0.58	0.58	No reliable evidence
Sales, 12 months after the report	10	−14.3%	−12.9%	80%	8	−1.81	0.11	No reliable evidence
Sales, 12 months after the trade	10	−13.6%	−13.5%	80%	8	−1.69	0.13	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.

Companies traded

Company	Title on the latest filing	Purchases	Sales	First report	Latest report
Medtronic MDT	SVP, Chief HR Officer	0	7	July 16, 2015	March 14, 2022
Best Buy BBY	EVP, Chief HR Officer	0	3	September 22, 2011	June 24, 2013

Trades and what followed

Moves are against the S&P 500; green means the trade went the insider’s way.

Reported	Traded	Company	Trade	Value	3 months after report	12 months after report	12 months after trade
March 14, 2022	March 11, 2022	MDT	Sale	$631,800	−3.6%	−16.9%	−17.5%
December 30, 2020	December 28, 2020	MDT	Sale	$1,723,500	−5.9%	−38.5%	−37.1%
June 2, 2020	May 29, 2020	MDT	Sale	$195,440	−2.0%	−6.7%	−8.9%
June 18, 2019	June 17, 2019	MDT	Sale	$878,940	+8.8%	−10.9%	−10.0%
March 6, 2018	March 2, 2018	MDT	Sale	$1,913,854	+6.1%	+11.0%	+14.8%
July 8, 2016	July 6, 2016	MDT	Sale	$852,252	−3.7%	−15.1%	−15.1%
July 16, 2015	July 14, 2015	MDT	Sale	$1,040,539	+0.3%	+13.0%	+15.1%
June 24, 2013	June 21, 2013	BBY	Sale	$390,485	+36.5%	−9.0%	−16.6%
May 28, 2013	May 24, 2013	BBY	Sale	$392,400	+30.9%	−15.0%	−12.0%
September 22, 2011	September 20, 2011	BBY	Sale	$276,490	−14.4%	−55.3%	−48.8%

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 Surface Carol A traded and do not suggest the use of non-public information. How every insider compares · the insider trading backtest.