Here is an excerpt from an article written by Margaret A. Neale and Thomas Z. Lys for Harvard Business Review and the HBR Blog Network. To read the complete article, check out the wealth of free resources, obtain subscription information, and receive HBR email alerts, please click here.

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How do companies end up with significant gender pay inequalities, if they don’t intend to discriminate against women? Here’s a simple economic model to show how this can happen:

Let’s assume your organization has two types of equally qualified and valuable potential hires – one has a low aversion to negotiating (let’s call them Type M), while the other (Type W) has a considerably higher aversion. Both will overcome this aversion if the gap between what they are worth (say $100,000) and what they’re offered is large enough. For Type M, let’s assume that the tipping point is $10,000. So Type Ms are likely to accept an offer of $90,000 without trying to negotiate. In contrast, the tipping point is $30,000 for Type W, which means they will accept a $70,000 salary without negotiating. If either type negotiates, they get what they are worth: $100,000.

Given these assumptions, the optimal strategy for the organization is to take advantage of the candidates’ aversion to negotiate, with potential savings of $10,000 for M types and $30,000 for W types. As a result, Type M candidates are offered higher starting salary ($95,000) than the Type W candidates ($80,000). This saves the company, on average, $5,000 per Type M hired and $20,000 per Type W hired, which results in Type Ms being paid $15,000 more than the Type Ws.

But this is just an economic model, right?

This hypothetical difference between types is consistent with the results of a study that found that women were willing to forgo as much as $1353 (for men, it was $666) to avoid the “pain” of negotiating when buying a car. And another study found that people behaved as this model predicts. More than 150 managers were asked to allocate a fixed pool of money for raises among equally skilled employees. When they were told that their employees could not negotiate, they gave male and female employees equal raises. When they were told they might have to explain the raise to workers and negotiate, they gave raises nearly 2.5 times larger to men.

Why the difference? One likely explanation is that the managers expected the men to question their raises and ask for more. So if they gave large enough raises to the men, fewer would be in their offices demanding explanations. Just as our model predicts, men got higher raises than women.

So what should women do?

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Neale and Lys then offer several plausible answers to that question. Here is a direct link to the complete article.

Margaret A. Neale is an Adams Distinguished Professor of Management at the Graduate School of Business at Stanford University. She is a co-author of Getting (More of) What You Want: How the Secrets of Economics and Psychology Can Help You Negotiate Anything, in Business and in Life (Basic Books, July 2015).

Thomas Z. Lys is Eric L. Kohler Chair in Accounting at the Kellogg School of Management at Northwestern University. He is a co-author of Getting (More of) What You Want.