Why do some people buy annuities while others don’t? The answer may have more to do with individual life expectancy and attitude than any specific annuity features or sales pitch, according to new research from Boston College’s Center for Retirement Research.

Karolos Arapakis and Gal Wettstein, both research economists at Boston College, published their results in January in a report titled “What Matters for Annuity Demand: Objective Life Expectancy or Subjective Survival Pessimism?”

They defined objective life expectancy as how long a person may reasonably anticipate living. Subjective survival pessimism, on the other hand, is a measure of the difference between actual life expectancy and how long a person thinks or feels they will live. Both are key determinants in whether or not someone chooses to buy an annuity, the researchers contended. Those with a higher objective life expectancy are more likely to invest in an annuity, primarily because many annuities pay a guaranteed lifetime income. The longer you live and receive payouts, the higher the yield on your investment.

Similarly, those who are pessimistic about their lifespan are less likely to want an annuity.

But objective life expectancy is more persuasive than subjective survival pessimism, the study concluded. A one-year increase in actual life expectancy increases the likelihood of buying an annuity by 0.2 percentage points, which may not seem like much but is almost nine times greater than a one-year decline in pessimism.

For a better understanding as to why, it’s important to understand how most annuities work. To an extent, annuity pricing and payout rates are determined by mortality pooling, sometimes called mortality credits. Essentially, the insurance company that provides the annuity figures that some annuitants will live longer than others, which of course is true. Those who live longer, who outlive their life expectancy, end up receiving a higher yield and directly benefiting from those who die earlier than expected.

So if you expect to live a long life, an annuity may well seem like a better deal. But is your expectation rational? “If demand for annuities is depressed largely because of irrational pessimism,” the study said, “perhaps such pessimism can be reduced through interventions that simply inform the public regarding mortality rates.” In other words, annuity providers and sales representatives could publicize actual life expectancies to reduce irrational pessimism.

If, however, people are realistic about their life expectancy and still resist buying an annuity, the problem may simply be that annuities are misunderstood or too expensive.

The researchers did not make specific recommendations to annuity purveyors. Rather, their analyses were more academic than practical. But there may be implications from their findings.

The study looked at surveys of people over age 50 that asked questions such as, “What’s the chance that you will live to age X?” Those between 55 and 70 tended to be on the pessimistic side about their life expectancy, whereas folks from 70 to 85 were more optimistic about living a long life. That held true regardless of gender, race, and education.

Comparing these statistics with annuity buying patterns indicated how both factors—objective life expectancy and subjective pessimism about life expectancy—are significant drivers of whether people choose to purchase an annuity. What’s more, they may also impact the percentage of their portfolios that they invest in annuities—that is, how much—with objective life expectancy playing the larger role.

The researchers noted, however, that these factors may not actually be causal. Pessimism about life expectancy “may be correlated with pessimism about other variables that affect annuity purchases,” they wrote, referring to factors such as health concerns and market volatility.