had new jobs to which they were scheduled to report within 30 days. Persons— whether or not attending school-who had new jobs not scheduled to begin until after 30 days (and not working or looking for work) are classified as not in labor force under both the new and old definitions.

Occupation, industry, and class of worker.-Occupation, industry, and classof-worker data apply to the job held in the survey week. Persons with two or more jobs are classified in the job at which they worked the greatest number of hours.

The major occupation groups used here are the same as those used in the 1950 census of population. The categories shown within some of the major groups are either detailed occupations or combinations thereof. The composition of these groups is available upon request from the Bureau of the Census.

The industry groups used here are mainly major groups used in 1950 census of population. The composition of the major industry groups is shown in volume II of the 1950 census of population.

The class-of-worker breakdown specifies "wage and salary workers," subdivided into private and government workers. "self-employed workers," and "unpaid family workers." Wage and salary workers receive wages, salary, commission. tips, pay in kind, or piece rates from a private employer or from a governmental unit. Self-employed workers have their own business, profession, or trade, or operate a farm, for profit or fees. Unpaid family workers work without pay on a farm or in a business operated by a member of the household to whom they are related by blood or marriage.

Hours of work.-The statistics on hours of work relate to the actual number of hours worked during the survey week. For persons working in more than one job, these figures relate to the number of hours worked in all jobs during the week. Average hours is an arithmetic mean computed from a distribution of single hours of work. Persons with jobs but not at work during the survey week are excluded from the computations.

Persons designated as working "full time" are those who worked 35 hours or more in the survey week; those designated as "part time" are persons who worked between 1 and 34 hours. Part-time workers are further classified by their usual status at their present job (either full time or part time) and by their reason for working part time during the survey week (economic or other reasons). "Economic reasons" include: Slack work, material shortages, repairs to plant or equipment, start or termination of job during the week, and inability to find fulltime work. "Other reasons" include labor dispute, bad weather, own illness, vacation, demands of home housework, school, etc., no desire for full-time work, full-time worker only during peak season, and other such reasons.

Duration of unemployment.-The duration of unemployment represents the length of time (through the current survey week) during which persons classified as unemployed had been continuously looking for work or would have been looking for work except for temporary illness, or belief that no work was available in their line of work or in the community. For persons on layoff, duration of unemployment represents the number of full weeks since the termination of their most recent employment.

Comparability with related data.-The employment data shown here were obtained by interview with occupants of household and will differ from employment data based on reports from individual business establishments and farms. "The Monthly Report on the Labor Force" provides information about the work status of the whole population, without duplication. Persons employed at more than one job are counted only once as employed, and are classified according to the job at which they worked the greatest number of hours during the survey week. Estimated based on report from business establishments and farms, on the other hand, count more than once persons who work for more than one establishment. Differences will also arise from the fact that other estimates, unlike those presented here, generally exclude private household workers, unpaid family workers, and self-employed persons, and may include workers less than 14 years of age. In addition, persons with a job but not at work are included with the employed in the estimates shown here, whereas only part of this group is likely to be included in employment figures based on establishment payroll reports.

For a number of reasons, the unemployment estimates of the Bureau of the Census are not directly comparable with the published figures for unemployment compensation claims or claims for veterans' readjustment allowances. In the first place, certain persons such as private household workers and State and local government workers are usually not eligible for unemployment compensation. Also, the qualifications for drawing unemployment compensation differ from the definition of unemployment used by the Bureau of the Census. For example, persons with a job but not at work and persons working only a few hours during the week are sometimes eligible for unemployment compensation, but are classified by the Bureau as employed. Furthermore, some persons may be reported as not looking for work even though they might consider themselves available for jobs and be eligible for unemployment compensation. Rounding of estimates.-Individual figures are rounded to the nearest thousand without being adjusted to group totals, which are independently rounded. Percentages are based on the rounded absolute numbers.

Reliability of estimates.-Since the estimates are based on a sample, they may differ somewhat from the figures that would have been obtained if a complete census had been taken using the same schedules, instructions, and enumerators. As in any survey work, the results are also subject to errors of response and reporting. These may be relatively large in the case of persons with irregular attachments to the labor market.

The standard error is primarily a measure of sampling variability, that is, the variations that might occur by chance because only a sample of the population is surveyed. As calculated for this report, the standard error also partially measures the effect of response and enumeration errors, but does not reflect any systematic biases in the data. The chances are about 68 out of 100 that an estimate from the sample would differ from a complete census by less than the standard error. The chances are about 95 out of 100 that the difference would be less than twice the standard error and about 99 out of 100 that it would be less than 2% times as large.

The estimates of standard errors shown in the following tables are approximations for the 330-area sample. Corresponding figures for the 230-area sample may be found in previous reports in this series. (See Current Population Reports, Series P-57, No. 16.) Table E shows the average estimates of standarà errors for the major employment status categories. The figures presented in Table F are to be used for other characteristics and are approximations of the standard errors of all such characteristics. In order to derive standard errors which would be applicable to a wide variety of labor force items and could be prepared at a moderate cost, a number of approximations were required. As a result, table F should be interpreted as providing an indication of the order of magnitude of the standard errors rather than as the precise standards error for any specific item.

TABLE E.-Standard error of major employment status categories

TABLE F.-Standard error of level of monthly estimates

The standard error of the change in an item from one month to the next month is more closely related to the standard error of the monthly level for that item than to the size of the specific month-to-month change itself. Thus, in order to use the approximations to the standard errors of month-to-month changes as presented in table G, it is first necessary to obtain the standard error of the monthly level of the item in table F, and then find the standard error of the month-to-month change in table G corresponding to this standard error of level. It should be noted that table G applies to estimates of change between 2 consecutive months. Changes between the current month and the same month last year, or between 2 other nonconsecutive months, will generally be subject to somewhat greater sampling variability than is indicated in table G.

Illustration.-Assume that the tables showed the total number of persons working a specific number of hours, as 15 million, an increase of 500,000 over the previous month. Linear interpolation in the first column of table F shows that the standard error of 15 million is about 160,000. Consequently, the chances are about 68 out of 100 that the figure which would have been obtained from a complete count of the number of persons working the given number of hours would have differed by less than 160,000 from the sample estimate. Using the 160,000 as the standard error of the monthly level in table G, it may be seen that the standard error of the 500,000 increase is about 135,000.

TABLE G.-Standard error of estimates of month-to-month change

The statistics by age and sex in table 2 are generally subject to smaller sampling variability than would be indicated by reference to tables F and G. The reductions are particularly large for estimates amounting to a substantial part of the total population in the specific age-sex category (for example, the number of males in the labor force in most age groups). For estimates comprising small proportions of the total population (such as the unemployed or certain categories of the group not in the labor force) the standard errors in tables F and G constitute satisfactory approximations.

The reliability of an estimated percentage, computed by using sample data for both numerator and denominator, depends upon both the size of the percentage and the size of the total upon which the percentage is based. Estimated percentages are relatively more reliable than the corresponding absolute estimates of the numerator of the percentage, particularly if the percentage is large (50 percent or greater).

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