How can the number of new jobs go up, but the unemployment rate get worse? If a person is working part time because full-time work is not available, is that person considered to be unemployed? How does the government know who didn't work anyway?

The nation's employment and unemployment statistics are perhaps one of the most familiar and least understood indicators the government uses to gauge the economy's health.

When the government measures unemployment, it doesn't count every person who is without work during every day of the month.

The Labor Department surveys about 59,500 selected households during one week every month. Each person of age 16 and older is classified as being employed, unemployed or not in the labor force, according to the department's definitions. People who hold more than one job are counted according to the job at which they worked the most hours.

The household is surveyed during the calendar week of the month in which the 12th day falls.

People are considered employed if they work full time; if they worked in their own business or profession or on a farm; or if they worked 15 hours or more in an enterprise operated by a member of their family, regardless of whether they were paid. A person is counted as employed even if he or she was on unpaid leave because of illness, bad weather, labor disputes or personal reasons.

People are unemployed if they had no job during the survamount for that time of year. This phenomenon occurs when the numbers have been "seasonally adjusted."

"Over the course of a year, the size of the nation's labor force and the levels of employment and unemployment undergo sharp fluctuations due to such seasonal events as changes in weather, reduced or expanded production, harvests, major holidays, and the opening and closing of schools," the Labor Department said.

"For example, the labor force increases by a large number each June when schools close and many young people enter the job market," Labor said. "The effect of such seasonal variation can be very large. Over the course of a year, for example, seasonality may account for as much as 95 percent of the month-to-month changes in unemployment."

These seasonal events follow a more or less regular pattern each year, so that by adjusting the statistics accordingly, trends such as the participation of women in the labor force or increases or declines in economic activity may be spotted more easily, the Labor Department said. Over a full year, the month-to-month adjustments balance out.