original series, that is, to derive series from which seasonal fluctuations have been removed insofar as possible. The only seasonally adjusted statistic regularly presented in this report is the unemployment rate in tables A and 1 (unadjusted rate also shown in tables 1 and 2). Other monthly estimates may be seasonally adjusted by dividing them by the corresponding adjustment factor for that month. For example, total civilian employment was estimated at 62,311,000 in March 1958 while the adjustment factor for total employment for that month (table D) is 97.7. Dividing the original estimate by the factor yields a seasonally adjusted employment figure for that month of 63,778,000. One way of describing that figure is to state that, on an annual average basis, total employment was at 63.8 million in March 1958. Seasonally adjusted estimates, like the original data on which they are based, are subject to sampling variability as well as response errors and biases. No specific computations have as yet been made to measure the sampling variability of the seasonally adjusted data, but it probably is not much different from that of the unadjusted figures (see tables E to G). For the seasonally adjusted rate of unemployment, changes from month to month would have to be almost twotenths of 1 percent before they could be regarded as statistically significant at the two-thirds confidence interval, one standard error). In evaluating deviations from the seasonal pattern—that is, changes in a seasonally adjusted series-it is also important to note that seasonal adjustment is merely an appropriation based on past experience. Furthermore, nonseasonal changes may be secular, cyclical, or irregular, or any combination of these fluctuations. Secular growth is exemplified by the expansion of the Nation's labor force over time as the population of working age continues to increase. Irregular phenomena, such as weather conditions, the timing of the survey week in relation to peak activity, strikes, etc., may cause departures from average seasonal expectations. TABLE D.-Seasonal adjustment factors for the labor force and its major Population coverage.-Except as otherwise specified, the data presented in this report relate to the civilian noninstitutional population of the United States 14 years of age and over which comprises all civilians living within the continental United States except inmates of penal institutions, homes for the aged, infirm, and needy, mental institutions, tuberculosis sanitariums, and similar places. A few of the tables include members of the Armed Forces as part of the categories "Total noninstitutional population” and “Total labor force.” Source of data.-The estimates are based on data obtained monthly in the current population survey of the Bureau of the Census. The current sample design, instituted in May 1956, is spread over 330 areas comprising 638 counties and independent cities, with coverage in each of the 47 States and the District of Columbia. Approximately 35,000 households are interviewed each month. Another 1,500 occupied units, on the average, are visited but interviews are not obtained because the occupants are not found at home after repeated calls or are unavailable for some other reason. There are also about 5,500 sample units in an average month which are visited but are found to be vacant or otherwise not to be enumerated. The previous sample design, in use from January 1954 through April 1956, was spread over 230 sample areas comprising 453 counties and independent cities. Data on the Armed Forces are obtained from the Department of Defense. Survey week.-Beginning with data for July 1955, the estimates relate to the calendar week (Sunday through Saturday) which contains the 12th of the month. For prior months, data relate to the calendar week containing the 8th of the month. Employment status concepts Employed.-Employed persons comprise those who, during the survey week, were either (a) at work, those who did any work for pay or profit, or worked without pay for 15 hours or more on a family farm or business; or (b) with a job but not at work, those who did not work and were not looking for work but had a jb or business from which they were temporarily absent because of vacation, illness, industrial dispute, or bad weather, or because they were taking time off for various other reasons. Proir to 1957, the statistics also included in the group "with a job but not at work" persons on layoff who had definite instructions to return to work within 30 days of the date of layoff-now classified as unemployed-and persons waiting to report to new wage and salary jobs scheduled to start within the following 30 days, now classified either as unemployed or (if in school during the survey week) as not in the labor force. Unemployed.-Unemployed persons include those who did not work at all during the survey week and were looking for work. Also included as unemployed are those who did not work at all during the survey week and (a) Were waiting to be called back to a job from which they had been laid off; or (b) Were waiting to report to a new wage or salary job scheduled to start within the following 30 days (and were not in school during the survey week); or (c) Would have been looking for work except that they were temporarily ill or believed no work was available in their line of work or in the community. Prior to 1957, part of group (a) above-those whose layoffs were for definite periods of less than 30 days-were classified as employed (with a job but not at work) rather than as unemployed, as were all of the persons in group (b) above (waiting to start new jobs within 30 days). Labor force. The civilian labor force comprises the total of all civilians classified as employed or unemployed in accordance with the criteria described above. The total labor force also includes members of the Armed Forces stationed either in the United States or abroad. Not in labor force.-All civilians 14 years of age and over who are not classified as employed or unemployed are defined as "not in labor force." These persons are further classified as "engaged in own home housework," "in school," "unable to work" because of long-term physical or mental illness, and "other." The "other" group includes for the most part retired persons, those reported as too old to work, the voluntarily idle, and seasonal workers for whom the survey week fell in an "off" season and who were not reported as unemployed. Persons doing only incidental unpaid family work (less than 15 hours) are also classified as not in labor force. Since January 1957, the category "not in labor force, in school," includes a small group formerly classified as employed (with a job but not at work), namely, persons attending school during the survey week who had new jobs to which they were scheduled to report within 30 days. Personswhether 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 1950census 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 21⁄2 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 |