Confidence Levels

For each of the estimates given in the tables, a 95-percent confidence range can be determined with the estimate at the mid-point. To calculate the 95-percent confidence range for a given figure:

1. Multiply the RSE row factor by the RSE column factor to determine the approximate RSE.

2. Multiply the approximate RSE (divided by 100) by the estimate given in the table to determine the approximate standard error.

3. Multiply the result by 1.96 to determine approximate 2 standard errors.

4. Subtract the result of Step 3 from the given estimate to determine the bottom of the range.

For example, to determine the confidence range for the estimated average expenditures for natural gas of $6.03 per million Btu in 1993 among U.S. households located in the suburban areas:

1. Multiply 1.9 (the RSE row factor) by 0.8 (the RSE column factor), which yields 1.52 percent (the approximate RSE).

2. Multiply .0152 (the approximate RSE) by $6.03 per million Btu (the estimate), which yields $0.091656 per million Btu (the approximate standard error).

3. Multiply $0.091656 per million Btu by 1.96, which yields $0.18 per million Btu (approximate 2 standard errors).

4. To determine the bottom of the range, subtract $0.18 per million Btu from $6.03 per million Btu, which yields $5.85 per million Btu.

5. To determine the top of the range, add $0.18 per million Btu to $6.03 per million Btu, which yields $6.21 per million Btu.

It can then be said with 95-percent confidence that, in 1993, the average expenditures for natural gas among U.S. households located in suburban areas fell between $5.85 and $6.21 per million Btu.