One of my all-time favorite investment quotes comes from famed Fidelity Magellan fund manager Peter Lynch: "Insiders might sell their shares for any number of reasons, but they buy them for only one: They think the price will rise."

Insider buying is an indicator you can use to screen for ideas. The most meaningful signal is when an executive or director buys shares on the open market just like you or me. It's too easy for management to build a sizable stake in the company by simply exercising stock options. On the other hand, when they open up their wallet and pay cold, hard cash for shares, that's important to notice -- especially if the purchase is large, which I loosely define at $500,000 or more.

By itself, insider buying is not a compelling enough reason for you to purchase shares. While management only buys if it thinks the stock will go up, you have to recognize that management may not be the best judge of what the company is worth. Even though they have an informational edge over you about the company's prospects, there is the risk that with a large part of their personal wealth on the line they have a biased view of the company's value and they are likely to overvalue the shares.

You can look for management buying as a signal that something good may happen for the company, but you have to take the next step of deciding for yourself if the stock is cheap. Two quick and dirty numbers you can look at are the company's free cash flow yield and where the stock is trading relative to its 52-week low.

The free cash flow yield is calculated by dividing the company's trailing-12-month free cash flow by its market cap. It is similar to the dividend yield with the difference being that it is measuring all of the excess cash generated by the company and not just the amount paid out to shareholders. As long as the company's prospects look stable, the higher the free cash flow yield the better. Renowned Fairholme fund manager Bruce Berkowitz uses a 10% free cash flow yield as a rough guide as to whether a stock is cheap.

The 52-week low is more of a measure of market sentiment toward the company than an indicator of value. Generally speaking, it's better to buy when the stock remains out of favor than after it has come roaring back from the bottom.

Company

Market Cap (millions)

Free Cash Flow (millions)

FCF Yield

Recent Stock Price

52-Week Low

% Change

Sizable Insider Buying Last 3 months

Quidel (Nasdaq: QDEL)

$388

$39

10.1%

$12.91

$10.48

23.1%

Yes

Thermo Fisher Scientific (NYSE: TMO)

$18,677

$1,319

7.1%

$44.95

$42.86

4.9%

No

Becton, Dickinson and Co. (NYSE: BDX)

$16,805

$1,286

7.7%

$71.16

$64.42

10.5%

No

Beckman Coulter (NYSE: BEC)

$3,193

$255

8%

$45.48

$44.40

2.4%

No

Source: Capital IQ, a division of Standard & Poor's, and author calculations.

Quidel Director Jack Schuler loaded up in June, buying $1.1 million worth of stock at an average price of $10.76. That has worked out well for him so far as Quidel shares have run up from their 52-week low. However, Quidel still has an attractive 10.1% free cash flow yield, so it may not be too late. Feel like giving Quidel a look?

Foolish conclusion
A large stock purchase from an insider is even better than a hot stock tip. Someone who knows the company intimately has made the decision to put a significant portion of their wealth on the line. I would much prefer to buy shares of a company where management is investing alongside me than in situations where the only shares management owns were given out by the company. Remember, Fools, insider buying is not the only measure you need to look at. It is a starting point for you to do additional research on the stock. Have any thoughts on Quidel? Share with the community in the comments section below.

Charly Travers does not own shares of any company mentioned in this article. Becton and Thermo Fisher are Motley Fool Inside Value selections. Try any of our Foolish newsletters today, free for 30 days. The Motley Fool has a disclosure policy.