Last week, Jews around the world observed Passover, the holiest event on the Judaic calendar.

Christians typically celebrate Easter around the same time, but this year the anniversary of Jesus Christ's rise from the dead fell in late March. (The two holy days will be much closer next year with Passover starting on April 9 and Easter on April 12.)

Jews and Christians also celebrate another pair of holidays that happen to fall close to one another: Christmas and Hanukkah, otherwise known as "Jewish Christmas."

What's interesting about this pair is that, unlike Passover, Hanukkah is not an important holiday for all Jews around the world, primarily just those in the U.S.

The reason for the disparity, say three Israeli economists at Stanford University, can be seen through the lens of competition. Much like Microsoft may update a product with a feature found in a competitor's program, U.S. Jews co-opted some of the consumer-friendly (i.e. giving lots of gifts to children) elements of Christmas in order to keep the religion attractive to younger generations and prevent children from feeling left out amid the December festivities.

Stanford's Ran Abramitzky, Liran Einav, and Oren Rigbi hypothesized that if such competition did exist, you'd likely find it among Jews who had children, were less religious, and, hence more likely to marry a shiksa or a shegetz.

But how do you measure Hanukkah celebration? By getting creative.

The U.S. National Jewish Population Survey asked about 5,000 Jews earlier this decade which holidays they celebrated, and, if Hanukkah was one of them, how many menorah candles they lit. The Festival of Lights is eight days long, so the Stanford researchers counted each lit candle as a unit of celebratory intensity.

They found that the effect of having children on how intensely a family celebrated Hanukkah was lowest among Orthodox Jews, got higher for Conservative Jews, and rose again for both Reform and non-religious Jews but to roughly the same level.

To make sure their results weren't merely showing that having children was the cause of more celebration, the researchers also looked at how likely respondents were to celebrate Passover and Rosh Hashana, two holidays not likely to be in competition with Christian rivals. They found that having children had much less of an effect on whether families celebrated these holidays.

So, if competition does indeed exist between Christmas and Hanukkah (at least for Jewish families that want their children to hold on to a Jewish identity), why isn't it the case for Passover with the major Easter typically so close?

It could be that Passover is just too important of a holiday for Jews to mess with, or it could be that Easter bunnies, scavenger hunts, and decorated eggs just don't have the same pull that Wiis and Play Station 3s do.