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level of employment; the sample is used to measure the month-to-month changes in the level.

Data for all months since the last benchmark to which the series has been adjusted are subject therefore to revision. To provide users of the data with a convenient reference source for the revised data, the BLS publishes as soon as possible after each benchmark revision a summary volume of employment, hours, earnings, and labor turnover statistics.

obtained which will provide coverage of a sufficiently large segment of the universe to provide reasonably reliable estimates that can be published promptly and regularly. The present sample meets these specifications for most industries. With its use, the BLS is able to produce preliminary estimates each month for many industries and for many geographic levels within a few weeks after reports are mailed by respondents, and at a somewhat later date, statistics in considerably greater industrial detail. The tendency of such a sample to produce biased estimates of the level of earnings for certain industries is counteracted by the stratified estimating procedure described under "Estimating Methods."

THE SAMPLE

Design

The sampling plan used in the current employment statistics program is an optimum allocation design known as "sampling proportionate to average size of establishment." The universe of establishments is stratified first by industry and then within each industry by size of establishment in terms of employment. For each industry the total size of the sample is distributed among the size class cells on the basis of average employment per establishment in each cell. In practice, this is equivalent to distributing the predetermined total number of establishments required in the sample among the cells on the basis of the ratio of employment in each cell to total employment in the industry. Within each stratum the sample members are selected at random.

Under this type of design, large establishments fall into the sample with certainty. The size of the samples for the various industries is determined empirically on the basis of experience and of cost considerations. In a manufacturing industry in which a high proportion of total employment is concentrated in relatively few establishments, a large percentage of total employment is included in the sample. Consequently, the sample design for such industries provides for a complete census of the larger establishments with only a few chosen from among the smaller establishments or none at all if the concentration of employment is great enough. On the other hand, in an industry in which a large proportion of total employment is in small establishments, the sample design calls for inclusion of all large establishments, and also for a substantial number of the smaller ones. Many industries in the trade and service divisions fall into this category. To keep the sample to a size which can be handled by available resources, it is necessary to accept samples in these divisions with a smaller proportion of universe employment than is the case for most manufacturing industries. Since individual establishments in these nonmanufacturing divisions generally show less fluctuation from regular cyclical or seasonal patterns than establishments in manufacturing industries, these smaller samples (in terms of employment) generally produce reliable estimates.

In the context of the BLS employment and labor turnover statistics programs, with their emphasis on pro

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500,000.

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Standard deviations of revisions

Finall

Preliminary

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500

2,500

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Reliability of the Employment Estimates

The estimates derived from the establishment survey may differ from the figures that would have been obtained if it were possible to take a complete census using the same schedules and procedures. The relatively large size of the BLS establishment sample assures a high degree of accuracy. However, since the link relative technique requires the use of the previous month's estimate as the base in computing the current month's estimate, small sampling and response errors may cumulate over several months. To remove this accumulated error, the estimates are adjusted annually to new benchmarks. In addition to the sampling and response errors, the benchmark revision adjusts the estimates for changes in the industrial classification of individual establishments (resulting from changes in their product which are not reflected in the levels of estimates until the data are adjusted to new benchmarks). In fact, at the more detailed industry levels, particularly within manufacturing, changes in classification are the major cause of benchmark adjustments. Another cause of differences, generally minor, arises from improvements in the quality of the benchmark data. (A detailed description of the March 1966 benchmark is available from the Bureau upon request.)

The entire difference between the estimate and benchmarks is assumed to have accumulated at a regular rate. Accordingly, the all employee series are adjusted by tapering out the differences for months between the current and the previous benchmark. The series for months subsequent to the benchmark month are revised by projecting the level of the new benchmark by the trend of the unadjusted series.

For the most recent months, national, State, and area estimates are preliminary and are so footnoted in the tables. These figures are based on less than the total sample and are revised when all the reports in the sample design have been received.

Approximations of the standard deviations (based on the experience of the last several years) of revisions

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STATISTICS FOR STATES AND AREAS

State and area employment, hours, earnings, and labor turnover data are collected and prepared by State agencies in cooperation with BLS. The area statistics relate to metropolitan areas. Definitions for all areas are published each year in the issue of Employment ana Earnings and Monthly Report on the Labor Force that contains State and area annual averages. Changes in definitions are noted as they occur. Additional industry detail may be obtained from the State agencies listed on the inside back cover of each issue. These statistics are based on the same establishment reports used by

ment, the sum of the State figures may differ slightly from the equivalent official U.S. totals on a national basis, because some States have more recent benchmarks than others and because of the effects of differing industrial and geographic stratification.

sections of this periodical, all the annual average data for the detailed industry statistics currently published by each cooperating State agency are presented (from the earliest date of availability of each series) in a summary volume published annually by the BLS.

UNEMPLOYMENT INSURANCE DATA

Insured unemployment represents the number of persons reporting a week of unemployment under an unemployment insurance program. It includes some persons who are working part time who would be counted as employed in the payroll and household surveys. Excluded are persons who have exhausted their benefit rights, new workers who have not earned rights to unemployment insurance, and persons losing jobs not covered by unemployment insurance systems (agriculture, State and local government, domestic service, self-employment, unpaid family work, nonprofit organizations, and firms below a minimum size). The rate of insured unemployment is the number of insured unemployed expressed as a percent of average covered employment in a 12-month period ending 6 to 8 months prior to the week of reference. Initial

claims are notices filed by those losing jobs covered by an unemployment insurance program that they are starting a period of unemployment. A claimant who continues to be unemployed a full week is then counted in the insured unemployment figure.

Because of differences in State laws and procedures under which unemployment insurance programs are operated, State unemployment rates generally indicate, but do not precisely measure, differences among the individual States. Persons wishing to receive a detailed description of the nature, sources, inclusions and exclusions, and limitations of unemployment insurance data should address their inquiries to Bureau of Employment Security, Washington, D.C.

SEASONAL ADJUSTMENT

Many economic statistics reflect a regularly recurring seasonal movement which can be estimated on the basis of past experience. By eliminating that part of the change which can be ascribed to usual seasonal variation, it is possible to observe the cyclical and other nonseasonal movements in the series. However, in evaluating deviations from the seasonal pattern--that is, changes in a seasonally adjusted series--it is important to note that seasonal adjustment is merely an approximation based on past experience. Seasonally adjusted estimates have a broader margin of possible error than the original data on which they are based, since they are subject not only to sampling and other errors but, in addition, are affected by the uncertainties of the seasonal adjustment process itself. Seasonally adjusted series for selected labor force and establishment data are published regularly in Employment and Earnings and Monthly Report on the Labor Force.

The seasonal adjustment method used for these series is an adaptation of the standard ratio-to-moving average method, with a provision for "moving" adjustment factors to take account of changing seasonal patterns. A detailed description of the method is given in the booklet, The BLS Seasonal Factor Method (1966), which may be obtained from the Bureau on request.

For establishment data, the seasonally adjusted series on weekly hours and labor turnover rates for industry groupings are computed by applying factors directly to the corresponding unadjusted series. However, seasonally adjusted employment totals for all

employees and production workers by industry division are obtained by summing seasonally adjusted data for the component industries. Indexes of aggregate weekly man-hours, seasonally adjusted, for mining, contract construction, and the major industries in manufacturing are obtained by multiplying average weekly hours, seasonally adjusted, by production workers, seasonally adjusted, and dividing by the 1957-59 base. For total, manufacturing, and durable and nondurable goods, the indexes of aggregate weekly man-hours, seasonally adjusted, are obtained by summing the aggregate weekly man-hours, seasonally adjusted, for the appropriate component industries and dividing by the 1957-59 base.

The seasonally adjusted establishment data for Federal Government are based on a series which excludes the Christmas temporary help employed by the Post Office Department in December. The employment of these workers constitutes the only significant seasonal change in Federal Government employment during the winter months. Furthermore, the volume of such employment may change substantially from year to year because of administrative decisions by the Post Office Department, Hence, it was considered desirable to exclude this group from the data upon which the seasonally adjusted series is based. Factors currently in use for the establishment data are shown in the September 1967 Employment and Earnings and Monthly Report on the Labor Force, and revisions will be made coincidental with the adjustment of series to new benchmark levels.

For each of the three major labor force components-agricultural and nonagricultural employment, and unemployment--data for four age-sex groups (male and female workers under age 20, and age 20 and over) are separately adjusted for seasonal variation and are then added to give seasonally adjusted total figures. In order to produce seasonally adjusted total employment and civilian labor force data, the appropriate series are aggregated. The seasonally adjusted rate of unemployment is derived by dividing the seasonally adjusted figure for total unemployment (the sum of four seasonally adjusted age-sex components) by the figure for the

seasonally adjusted civilian labor force (the sum of twelve seasonally adjusted age-sex components).

The seasonal adjustment factors applying to current data are based on a pattern shown by past experience. These factors are revised in the light of the pattern revealed by subsequent data. Revised seasonally adjusted series for major components of the labor force based on data through December 1967 are published in the February 1968 Employment and Earnings and Monthly Report on the Labor Force. Revisions will be made annually as each additional year's data become available.

ATTENTION

As discussed in the Technical Note, the Bureau periodically adjusts the industry employment series to a recent benchmark to improve their accuracy. These adjustments may also affect the hours and earnings series because employment levels are used as weights. Industry data for all national series shown in this report have been adjusted to March 1966 benchmarks. Data from April 1966 forward are subject to revision at the time of the next benchmark.

Beginning with the September 1967 and subsequent issues of Employment and Earnings and Monthly Report on the Labor Force, the national data in sections B, C, and D supersede those published in previous issues, as well as those appearing in the Handbook of Labor Statistics, 1967. Comparable data are published in Employment and Earnings Statistics for the United States, 1909-67, BLS Bulletin 1312-5.

Industry titles conform to the Bureau of the Budget's standard list of short SIC titles,

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