The auguries of political science strongly predict that the Arab Spring rebellions will succumb to new autocrats in the near term. Sparked by a 2010 uprising in Tunisia, the Arab Spring revolutions toppled autocratic regimes not only in Tunisia but in Egypt, Yemen, and (with outside military assistance) Libya, while civil war broke out in Syria.

So why the gloom over the hopes for a wave of Arab democratization? Because, broadly speaking, data on the arcs of post–World War II revolutions suggests that their chances of successfully transitioning from autocracy to democracy are less than 50/50.

That dispiriting appraisal is based on a new data set, compiled by the UCLA political scientist Barbara Geddes and her colleagues, that provides transition information for the 280 autocratic regimes (in 110 countries with a population of more than a million) in existence from 1946 to 2010. More than half of the time, one autocrat has been followed by another. The odds of transitioning from autocracy to democracy are even worse for personalist dictatorships and one-party states, although military dictatorships make the transition about two-thirds of the time. A personalist dictator is a ruler who basically runs the state as a family business. As it happens, all of the regimes in which Arab Spring revolutions were successful were more or less personalist dictatorships: Muammar Qaddafi in Libya, Zine El Abidine Ben Ali in Tunisia, Hosni Mubarak in Egypt, Ali Abdullah Saleh in Yemen, and Bashar Hafez al-Assad in Syria.

Besides the dismal record of revolutions of gone bad, four other social and political characteristics help stake the deck against these Arab states: youth, past democratic history, income, and complexity.

Youth: The George Mason University political scientist Jack Goldstone argues that the low median age of these countries' populations lessens the probability that they will successfully negotiate a transition to democracy. That would follow the pattern spotted by the Stuttgart University researcher Hannes Weber, who in a 2011 study in the journal Democratization looked at data from 110 countries between 1972 and 2009. "Democratic countries with proportionally large male youth cohorts are more likely to become dictatorships than societies with a smaller share of young men," he writes.

Why? One hint might be found in an intriguing 2012 study, "On Demographic and Democratic Transitions," by the London School of Economics population researcher Tim Dyson. Dyson contends that it is no accident that the shift toward lower fertility rates coincided with the rise of democracy in Western Europe. Falling fertility signals that people are gaining more control over their lives. "As the structure of a society becomes increasingly composed of adult men and women, autocratic political structures are likely to be increasingly challenged and replaced by more democratic ones," Dyson argues. The median ages of Tunisia, Libya, Egypt, Syria, and Yemen are 30, 25, 25, 22, and 18 years, respectively. For comparison, the median age of the European Union is 41 years and the United States' is 37 years.

History: The fact that none of the Arab regimes have had much past experience with democracy also suggests that their revolutions are probably doomed to devolve into autocracy, at least in the short run. Goldstone maintains that former communist states in central Europe and the Baltics had smoother transitions to democratic regimes than did those of Central Asia and the Balkans because they had some involvement with democratic institutions before the Iron Curtain fell.

How big has the Arab democratic deficit been? The Polity IV Index measures countries on a scale in which -10 indicates total autocracy and +10 signals full democracy. In 2011, the Dubai Economic Council macroeconomist Ibrahim Elbadawi and his colleagues reported that the Arab countries entered the 1960s with an average polity index score of -5.3—and by 2003 that score had fallen to a -5.5. In other words, while much of the world was democratizing at the end of the last century, Arab countries as a whole had become more authoritarian.

Income: A 2006 study by the Columbia University political scientist David Epstein and his colleagues found that political regimes have a greater propensity to become and remain democratic as per capita incomes increase.

Back in 2000, the New York University political scientist Adam Przeworski and his colleagues claimed to have identified an income threshold above which no democratic country had ever reverted to autocracy: About $6,000 per capita GDP ($,8,100 today). "Democracies never die in wealthy countries," they asserted. According to the World Bank, the current per capita GDPs of Yemen, Syria, Egypt, and Tunisia, are $1,500, $3,300, $3,200, and $4,200 respectively. Given Libya's continuing political chaos, the Bank doesn't estimate its per capita GDP, but other sources report that it has fallen by about half to $6,000. None of the Arab Spring countries are now above the democratic consolidation threshold.

Complexity: It is harder to build democratic institutions than it is for a strongman and his thugs to impose his rule on a country. In their 2012 study, "Complexity and the Limits of Revolution: What Will Happen to the Arab Spring?," the New England Complex Systems Institute researchers Alexander Gard-Murray and Yaneer Bar-Yam analyzed data tracking regime changes in the 10 years following revolutionary events in countries around the world during the period between 1945 and 2000. They find, "In these events higher levels of disruptive violence result in greater incidence of autocratic outcomes." The revolutions in Yemen, Libya, and Syria were or are all notably violent.

The uprisings in Egypt and Tunisia were relatively peaceful, but the ousting of President Mohamed Morsi by Egypt's army in July and a recent spate of assassinations in Tunisia dim the prospects of near-term democratic consolidation in both countries. As a consequence of their analysis, the two researchers infer that the "new governments are danger of facing increasingly insurmountable challenges and reverting to autocracy."

Why? Revolutions often flatten the state's institutions leaving little for the victors to use for governance. When post-revolutionary social, political, and economic turmoil causes hope for better lives to falter, weary populaces often look for a "man on horseback" to rescue them and restore order. Democratic institutions must take into account a wider range of social, political, and economic interests and are thus much more complex than autocracies.

In contrast to the Arab Spring countries, the two complexity researchers agree with Goldstone and observe that the relatively peaceful revolts against the Communist regimes in Eastern Europe left intact most of the governance apparatus of those states. These institutions were then successfully adapted, with the guidance of the European Union, to democratic norms.

Why hasn't the Arab Spring spread to other Arab autocracies? Aren't the Arab monarchies personalist regimes too? Goldstone argues that monarchies tend to have "a reservoir of nationalist, ethnic, or religious legitimacy due to their traditional leadership role." In addition, Arab monarchs can deflect popular protests by blaming prime ministers or even offering a bit of power sharing. Goldstone also points out the oil-rich monarchies in Oman, Saudi Arabia, and Kuwait had the money to buy off their restive populations. For example, Saudi King Abdullah showered $37 billion in house-building and job creation schemes on his 18 million subjects. Similarly, Murbarak and Qaddafi tried to bribe support by promising to boost the salaries of government employees. But handing out wads of cash to bureaucrats was not enough to save those upstarts.

Goldstone further contends that Lebanon, Algeria, the Palestinian Authority, Morocco, and Iraq remained relatively calm largely because their peoples are fatigued by their own recent political upheavals.

Goldstone also offers an interesting analysis of the feckless role that the United States has played in the region helping to fuel the revolts. U.S. foreign and military aid enables dictators to bribe opponents for a while but ends up making them appear as U.S. stooges to their people. Once the despots are dependent on U.S. largesse, our government demands that they begin to liberalize. This weakens the fear that underpins their regimes and so they fall. "In times when the United States seemed satisfied with lip service regarding protection of human rights and democratization," writes Goldstone, "the United States came to be viewed by domestic elites and popular groups as an insincere and untrustworthy advocate of popular rights and national self-determination." In the wake of the Arab Spring, that appraisal sounds all too right as the Obama administration floundered about seeking haphazardly to join a parade that had already taken off.

So are Arab countries perpetually doomed to rule by autocrats? Not necessarily. The overall trend is for more and more countries to become and remain free. According to the think tank Freedom House, only 29 percent of the world's countries were free in 1973, 25 percent were partly free, and 46 percent were not free. By 2013, 46 percent were free, 30 percent partly free, and 24 percent not free.

The taste of liberty, however fleeting, sharpens the appetite for more. Eventually, Arab peoples will depose their dictators and join the growing ranks of free countries.