NEW YORK ( InsiderMonkey) -- Academic studies have shown that insider trading is most profitable when several insiders buy around the same time. A study by University of Illinois professor Josef Lakonishok and his student Inmoo Lee shows that insider purchases generate more than 7% a year in excess returns above index funds when there are several insiders purchasing. Insider Monkey recently let you know about one company with insider purchases. Hercules Technology Growth Capital ( HTGC) closed at $10.36 the Friday before we reported the insider purchase. During the past week the stock increased by 4.3% beating the S&P 500 , which increased by 1.1%. This is the fifth week in a row our list of insider purchases has beaten the S&P 500. Seventeen of the 22 stocks that made our list managed to beat the index. Insider Monkey compiled a list of companies with at least three insiders buying with the latest purchase made in late November. Here are the most recent stocks insiders are buying like crazy: Winmark ( WINA) insiders have been since Dec. 22. The stock closed at $33.16 last Friday. Trailer Bridge ( TRBR) have been both buying and selling around $3. Douglas E. Schimmel purchased 30,000 shares at $2.91 on Thursday. The stock closed at $2.94 on Friday. There have been recent insider purchases of Cogent Communications ( CCOI) around $14 a share. The stock closed at $13.74 on Friday, less than what the insiders paid for it. Diamond Foods ( DMND) had significant insider purchases three months ago when it was trading around $41. More recently, Diamond Foods' Chairman and CEO Michael Mendes purchased additional shares below $52. On Friday, the stock closed at $52.30. There have been recent insider purchases in EQT ( EQT). The largest transaction was two months ago at $38.38; recent transactions occurred below $45. On Friday, the stock closed at $45.62. >To see these stocks in action, visit the 5 Stocks Insiders Are Buying portfolio on Stockpickr. This article was originally published at Insider Monkey.