Many of those in their pre-retirement years still show a lack of understanding of some key retirement considerations, according to the MetLife Mature Market Institute, which has posted online its Retirement Income Quiz that previously had been administered in survey form.

For example, only 28 percent know that the average cost of a year in a nursing home is about $84,000, with 16 percent believing the figure to be as low as $44,000. (However, 57 percent did understand that health insurance and disability insurance do not cover long-term care insurance needs.) Fewer than half, 45 percent, know that experts suggest that 80 percent or more of pre-retirement income is needed for retirement, with nearly half saying less is needed and only 6 percent saying more is needed.

Only a third knew that a person at age 65 has a 50 percent chance of living past age 85, with almost all of the rest believing the chances are lower than that. And four-tenths believed that more than the 4-6 percent recommended by experts can be drawn from retirement savings each year while assuring sufficient retirement income for life. Nor did most understand how much they would benefit from deferring the start of receiving Social Security benefits past the normal age for claiming them.

Such opinions could leave individuals retiring without being fully prepared and potentially in for unpleasant surprises once they are retired.