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 unemploy ment. A claimant who continued to be unemployed a full week is then counted in the insured unemployment figure.

Because of differences in State laws and procedures under

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 limitation of unemployment insurance data should address their inquiries to Manpower Administration, Washington, D.C. 20210.

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 patternthat 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.

The seasonal adjustment methods used for these series are 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 two publications, BLS Seasonal Factor Method (1966) and X-11 Variant of the Census Method II Seasonal Adjustment Program, Technical Paper No. 15, Bureau of the Census (1967).

Data for the household series are seasonally adjusted by the Census X-11 Method. For each of the three major labor force components-agricultural employment, nonagricultural employment, and unemployment-data for four age-sex groups (male and female workers, 16-19 years and 20 years and over) are separately adjusted for seasonal variation and 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 for all civilian workers is derived by dividing the figure for total unemployment (the sum of four seasonally adjusted age-sex components) by the figure for the civilian labor force (the sum of 12 seasonally adjusted age-sex components). Other series, such as unemployment by duration or employment by major occupational groups, are independently adjusted.

The seasonal adjustment factors applying to current data are based on a pattern shown by past experience. Once each year (in January), these factors are revised in the light of the

previous years' experience. Revised seasonally adjusted serie for major components of the labor force based on data through December 1973, plus a short description of the methodology. are published in the February 1974 Employment and Earnings. Many additional series, which are either components or aggregates of the series presented, are available from the BLS upon request.

For establishment data, the seasonally adjusted series on hours, hourly earnings, and labor turnover rates for industry groupings are computed by applying factors directly to the corresponding unadjusted series, utilizing the BLS Seasonal Factor Method. 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. Seasonally adjusted average weekly earnings are the product of seasonally adjusted average hourly earnings and average weekly hours. Average weekly earnings in constant dollars, seasonally adjusted, are obtained by dividing seasonally adjusted average weekly earnings by the seasonally adjusted Consumer Price Index. Indexes of aggregate weekly man-hours, seasonally adjusted, are obtained by multiplying aver age weekly hours, seasonally adjusted, by production or nonsupervisory workers, seasonally adjusted, and dividing by the 1967 base. For total private, total goods producing, total private service producing, trade, 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 1967 base.

The seasonally adjusted establishment data for Federal Government are based on a series which excludes the Christmas temporary help employed by the Postal Service 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 Postal Service. Hence, it was considered desirable to exclude this group from the data upon which the seasonally adjusted series is based.

The revised seasonally adjusted series for the establishment data reflect experience through March 1973. Seasonal factors to be used for current adjustment appear in the June 1973 Employment and Earnings.