In a victory for common sense, the trading behavior of company executives, directors, and large shareholders in the stocks of firms they're registered "insiders" at have been proven profitable to monitor by both academic studies and (more importantly) the experience of your fellow professional investors.

Below are lists of the top 10 mainly open-market insider purchases and sales filed at the Securities and Exchange Commission Wednesday, February 20, 2013 as ranked by dollar value.

Please note, however, that these are factual lists, not buy and sell recommendations. Dollar value is only one metric to assess the importance of an insider transaction, and, frankly, often not even the most important metric that determines if an insider transaction is significant.

In insider purchases, multi-national pharmaceutical company GlaxoSmithKline (NYSE:GSK) bought $2,567,090 worth of Theravance (NASDAQ:THRX), of which it is a beneficiary owner.  Theravance specializes in small molecule medicines intended for the therapy of respiratory diseases, bacterial infections, and central nervous system pain. Investment management firm Cannell Capital, beneficiary owner of voice, data, and video service provider Multiband (NASDAQ:MBND), bought $444,706 worth of the company. Thomas Siering, President and CEO of real estate investment trust Two Harbors (NYSE:TWO), bought $211,680 worth of company stock.

In insider sales, Apollo Management Holdings GP, a beneficiary owner of LyondellBasell (NYSE:LYB), sold $1,532,000,000 worth of company stock. LyondellBasell manufacturers chemicals and polymers, refines crude oil, produces gasoline blending components, and develops technologies for the production of polymers. At Sensata Technologies (NYSE:ST), which manufactures and sells sensors and controls, beneficiary owner Bain Capital sold $953,033,984 worth of company stock. At health care services company HCA (NYSE:HCA), there were two big sales, with KKR Millennium Fund selling $856,746,048 worth of company stock and Bain Capital selling $845,746,048 worth of company stock. There were also two sales at LinkedIn (NYSE:LNKD), with Co-Founder and Director Reid Hoffman selling $13,276,458 worth of company stock and CEO Jeff Weiner selling $6,424,900 worth of company stock.

At InsiderInsights.com, we find new investment ideas just about every day using these and more intricate insider screens to determine where we should focus our subsequent fundamental and technical analysis. And while stocks don't (or shouldn't) move up or down based on insider activity alone, insiders tend to be good indicators of when real stock-moving events like earnings surprises, corporate actions, and new products may be in the offing.

Insider Purchases

#:	Filer Name	Insider Titles	Company Name	Ticker	Trans Type	Dollar Value
1	Glaxosmithkline	BO	Theravance	THRX	B	$2,567,090
2	Cannell Capital	BO	Multiband	MBND	B	$444,706
3	Siering Thomas	CEO,PR,DIR	Two Harbors	TWO	B	$211,680
4	Eberwein Jeffrey	BO	Endeavour Intl	END	B	$172,600
5	Frost Phillip MD	CEO,CB,BO	Opko Health	OPK	B	$168,553
6	Wulff John K	DIR	Moodys	MCO	B	$140,250
7	VN Capital Mgt	BO	Breeze Eastern	BZC	B	$125,181
8	Sherwin Elton	DIR	Peregrine Semi	PSMI	B	$111,090
9	Rosenberg Sheli Z	DIR	Nanosphere	NSPH	B	$98,745
10	Thornley Anthony S	DIR	Peregrine Semi	PSMI	B	$92,500

Source: InsiderInsights.com | Key to Insider Title and Trans Type Codes

Insider Sales

#:	Filer Name	Insider Titles	Company Name	Ticker	Trans Type	Dollar Value
1	Apollo Mgt Gp	BO	Lyondellbasell	LYB	JS*	$1,532,000,000
2	Bain Capital	BO	Sensata Tech	ST	JS*	$953,033,984
3	Kkr Millennium Fund	BO	HCA	HCA	JS*	$856,746,048
4	Bain Capital	BO	HCA	HCA	JS*	$845,689,728
5	Blackstone Mgt	BO	Team Health	TMH	JS*	$318,450,368
6	Hoffman Reid	DIR,BO	Linkedin	LNKD	AS	$13,276,458
7	Hayford Michael D	VP,CFO	Fidelity Natl Info	FIS	S	$13,228,201
8	Redstone Sumner M	CB,DIR,BO	CBS	CBS	JS*	$12,468,440
9	Weiner Jeff	CEO,DIR	Linkedin	LNKD	AS	$6,424,900
10	National Health	BO	National Health	NHC	JS*	$4,700,000

Source: InsiderInsights.com | Key to Insider Title and Trans Type Codes

Editor's note: Jonathan Moreland is the founder of Insider Insights and author of "Profit From Legal Insider Trading."