# Unit of Measure

The "Level" is the value of the selected statistic in each area for the year selected.

The "Percent change from preceding period" unit of measure is the period to period change for the statistic selected. The first period that you select is used as the base period, and a percent change from preceding period will not be calculated for that period.

The "Percent of U.S." unit of measure is the share that each state or local area has of the national total for the statistic selected. For each state, the Percent of U.S. unit of measure is computed as the state level for the selected statistic divided by the U.S. level for the selected statistic, with the resulting quotient then multiplied by 100 to convert it to a percentage value.

The "Percent of U.S. Metro Portion" unit of measure is the share that each metropolitan statistical area (MSA) has of the U.S. metropolitan portion total for the statistic selected, with the resulting quotient then multiplied by 100 to convert it to a percentage value.

The "Percent of State" unit of measure is the share that each county has of the state total for the statistic selected, with the resulting quotient then multiplied by 100 to convert it to a percentage value.

The "Compound annual growth rate" unit of measure is the only item for which you need to select two years, a "Begin year" and an "End year." The compound annual growth rate will then be computed for the statistic you have selected. The compound annual growth rate is computed as an annually compounded rate, not as a simple arithmetic average of the annual growth rates. It is the nth root of the ratio of the ending value to the beginning value, minus 1.0, and times 100 (to express the value as a percent per year), where the "n" in "the nthroot" is equal to the end year minus the begin year. Algebraically, the compound annual growth rate for a value is computed as (((End value / Begin value)^p/n )-1)*100, where p=periodicity (4 for quarterly, 1 for annual).

The "Index" unit of measure relates the value of a variable (or group of variables) to a base level. The base level is set so that the index produces results that are easy to understand and compare. The base level will always be the first period you selected.

The formula for calculating an index is as follows:

x_{1}=(dv1/dv1)*100 = 100

x_{2}=(dv2/dv1)*100

x_{3}=(dv3/dv1)*100

x_{1} = index of first year selected, x_{2} = index of second year ...

dv_{1} = datavalue for first year selected, dv_{2} = datavalue for second year ...

The "Industry specialization index" (ISI) is a measure of the degree to which states are more or less specialized in an industry. The more specialized a state is in an industry, the higher the ISI will be. The ISI is computed as the share that an industry is of a state divided by the share that the industry is of the nation, and the resulting quotient multiplied by 100. If an industry is a greater share of a state than it is of the nation, its ISI will be greater than 100; if an industry is a smaller share of the state than it is of the nation, its ISI will be less than 100. The industry specialization index is sometimes called a "location quotient" or "LQ." NOTE: The Industry specialization index unit of measure is not meaningful for the statistic Real GDP by state or for the statistic Chain-type quantity indexes.