Too much has been written about the gender pay gap; too much because what has been written is often wrong and hysterical about a subject which has a completely innocuous explanation. What the Left has written about this topic is like everything else they write: a chaotic mess of lies, and illusions arising from their own ignorance.

And just as the Left brings about chaos, the Right fails to counter effectively. In their attempt to debunk the existence of the gender gap, the Right falls short in the argument because it acts out of defensive impulses. This is in keeping with the perpetual historical theme of the modern Right, both mainstream and fringe – inadequacy.

The standard, incomplete, conservative arguments made to debunk the existence of a pay gap between men and women – failures of studies to use the right control groups, wrongly equating qualitatively different types of work as similar, test scores, differences in psychology between genders – have been proposed, but are still lacking.

These points are often true, but after these factors are added a pay gap of more or less 20 cents to the dollar remains.

There is still a missing factor that after being controlled for nearly eliminates the gap, reducing it to only a few cents.

That factor is the reduction in time women spend working after giving birth.

For proof, which should put the issue of the pay gap to rest for good, we turn to a study titled Dynamics of the Gender Gap for Young Professionals in the Financial and Corporate Sectors (2010).

The study surveyed MBA alumni from the exclusive Booth School of Business of the University of Chicago who had graduated between 1990 and 2006. Following their graduation the careers pursued by these MBAs were primarily with top firms in the elite value transference fields of financing, corporate services, and consulting. These fields have often been the target of so many accusations made by feminists for being unfairly dominated with male-workaholics. And the pay gap, which exists, is wrongly put forward as proof of their misogyny.

Using regression analysis, the authors controlled for the standard independent variables in gender gap research: GPA, type of courses, GMAT scores, age, race, marital status, pre-MBA and post-MBA work history, years since graduation, job function, employer type, and others.

After these causal factors had been controlled for in their statistical model the authors still found a gender gap in income outcomes.

What eliminated the gap to a statistically insignificant 3 to 5 cents was the addition to the model of time variables measuring how long men and women spent out of the workforce.

Women MBAs in their sample, of course, had after giving birth tended to spend more time over their career out of the workforce than male MBAs. After maternity leave women also tended to later cut back on their hours worked, if they returned:

Labor supply factors explain most of the remaining gender gap in earnings. The inclusion of a full set of dummy variables for weekly hours worked reduces the raw gender gap of 29 log points (column 1) to 17 log points (column 4). Adding hours worked to the specification including pre-MBA characteristics and MBA performance lowers the remaining gender gap to 9 log points (column 5). The gender earnings gap is reduced to just 6.4 log points (column 6) with the further addition of a quadratic term for post-MBA years of actual work experience and a dummy variable for the presence of any post-MBA career interruption. Augmenting the model with (arguably even less exogenous) variables to control for reasons for choosing one’s current job, job function, and employer type further reduces the coefficient on the female dummy to a (statistically insignificant) –3.8 log points (column 8).[1]

What this means for conservatives, and what should be the end of the debate, in plain English:

There is no statistically significant earnings gap between men and women in the same type of work, with the same experience, and the same amount of hours worked.

More basically:

There is no statistically significant earnings gap between men and women in the same type of work, with the same experience, and if women do not have children.

The political implications of this study are obvious.

First, this proves that the pay gap is not the result of bias against women in male-dominated fields.

Secondly, women were not unfairly penalized for spending time giving birth to and caring for children. Statistically, men suffered a higher reduction in their hourly earnings than women for taking time out of the work force.

Lastly, and most importantly in the policy debate the gap has raised, there is nothing an employer can do to eliminate the gap.

Employers cannot advise their women associates to not have children in order to equalize their lifetime earnings with those of with men without risking a discrimination lawsuit and a publicity scandal. Businesses are also unable to force mothers under their employ to not take time off or not reduce their hours worked after giving birth without risking a discrimination lawsuit and a publicity scandal.

The decision to have children, and suffer the reduction in income that is very likely to follow birth, is entirely under the control of women associates and out of the hands of their employers.

At best an employer can reduce the total amount of time spent out of the workforce with better maternity and child care benefits. But this cannot completely eliminate the decision of most women to reduce work hours after having children even with the most generous child care package. Even a small reduction in hours has a statistically significant impact on earnings, and most new working mothers will be sure to spend some time off.

The theory that women receive unequal pay, for equal work and equal hours, is false.

To the extent policy can narrow this gap, the gap can only be minimized, never closed.