**Errors of Nonobservation**

Finally, several potential sources of nonsampling error and bias result from errors of
nonobservation.  The 1994 MECS represents, in terms of sampling coverage, the mail
frame of the 1994 ASM or 98 percent of the manufacturing universe, which is consistent
with the 1991 MECS.

**Unit Nonresponse**

Even though the MECS is a legislatively mandated survey and sampled establishments are
given sufficient opportunity and time to respond, nonresponse occurs in the MECS and is
accounted for in a nonresponse adjustment of sampling weights. Clearly, had these
adjustments not been performed, the estimates produced from only the responding
establishments would not have been representative of the target universe for the MECS.
Such estimates would have been biased. Adjusting the sampling weights to reflect the
target universe is an attempt to mitigate the potential effects of such a bias.

Adjustment factors are calculated for each of the 72 published strata to account for
the variation of nonresponse between strata. Each stratum represents a relatively
homogeneous subgrouping of establishments with respect to primary product output and level
of fuel consumption.

Implicit in that procedure is the assumption that primary product output and level of
fuel consumption are highly correlated with energy expenditure patterns, so that the
establishments within a stratum would also be homogeneous with respect to the quantities,
types, and shares of energy consumed as fuels and for nonfuel purposes. Also, the weight
adjustment method assumes that the relationship between survey variables of interest and
the control variable used for constructing the adjusted sample weight is the same for the
population covered by MECS respondents within an adjustment stratum as it is for the rest
of the population within that stratum.

To the extent that the nonresponding establishments within the adjustment stratum share
the energy expenditure patterns of the responding establishments within the strata, the
resulting adjustments to the MECS estimates will tend to be minimally biased. If, on the
other hand, the energy expenditure patterns of the responding and nonresponding
establishments differ substantially, the resulting adjustments are potentially biased, and
the overall estimates may not accurately represent the originally targeted MECS universe.

****

**Item Nonresponse**

Item nonresponse is the type of nonresponse that occurs when an item (or several items)
is missing in an otherwise completed questionnaire. In 1994, MECS expanded its collection
of establishments' characteristics. MECS now collects economic information, such as
floorspace, motor purchase evaluations, reasons for fuel switching, energy management
activities, and energy efficient technologies. Although a Response Analysis Survey of 1991
respondents indicated that a record-keeping system tracked these items, some
establishments did not have a record-keeping system which would have enabled them to
respond to these types of questions. To the extent that information systems excluded
economic items, the MECS incurred item nonresponse.

Some surveys impute values for item nonresponse. The MECS did not impute for most of
these missing items. The complexities and inherent heterogeneity of manufacturing
establishments prevent the use of imputation techniques for most of these missing items.
However, budget restrictions and timeliness issues halted respondent recontacts before
item nonresponse could be eliminated.

MECS has a full reporting of energy consumption from all responding establishments.
However, economic variables (such as value of shipments and value added) have historically
been obtained from the Annual Survey of Manufactures (ASM). The change in sampling frames
from the ASM to the CM had an indirect result on item nonresponse; that is, some
establishments in the MECS sample did not have economic data (value of shipments and value
added) because they were not included in the 1994 ASM sample. One approach considered by
EIA was to query these establishments on their shipments. Unfortunately, duplication
issues with the ASM precluded the MECS from querying establishments on their shipments and
value added. Hence, these establishments did not have the ability to report their economic
data.

Unlike the establishment characteristics, like floorspace, value of shipments and
value-added estimates were imputed for all MECS establishments that were not in the
sample. Of the 19,292 MECS sample respondents, 13,011 cases have ASM-reported value of
shipments data and ASM-reported value-added data. Of the remaining cases, we only have the
total number of employees and payroll from the Standard Statistical Establishment List
(SSEL). Using aggregate payroll data, by industry (at the four-digit SIC level), value of
shipments and value added were imputed by forward indexing. Using value added as an
example, this imputation technique is expressed as



where SW94 is payroll from the 1994 SSEL and SW92 and VA92
are payroll and value added from the 1992 Census of Manufactures (CM). Value of shipments
was imputed analogously.

The imputation model was evaluated by testing how well it predicted known 1994 ASM
value-added data. Matching was done for SIC industries 2000 through 3999. If an
establishment was indicated as out-of-business, the observation was deleted. If the ratio
SW94/SW92 was less than 1/8 or more than 8, the data were considered
either as outliers or as recording errors. Such observations (696 out of 52,227) were
removed prior to analysis.

A paired comparison t-test was done for the percent difference between VAimp
and actual VA94 to determine if the mean percent difference was statistically
significant from zero. At a 95-percent confidence level, the null hypotheses (the mean
percent difference between VAimp and actual VA94 is zero) could not
be rejected. Hence, there was no difference statistically between Vaimp and VA94.
A t-test using value of shipments yielded the same conclusion.

Table 1 provides the counts, percents, and weighted percents for the imputed estimates
of value of shipments and value added by industry.

More detailed information on sources of nonsampling error in the MECS can be found in
the methodological report.

|**Table 1. Number of Establishments and Weighted and
    Unweighted Percentages of the Imputed Value of Shipments and Value Added**
|------------------------------------------------------------------------------------------------------------------------------------
|**SIC****Code**                                                                                                                     
|**Number of Establishments**                                                                                                        
|                                                                                                                                    
|2011                                                                                                                                
|2033                                                                                                                                
|2037                                                                                                                                
|2046                                                                                                                                
|2051                                                                                                                                
|2061                                                                                                                                
|2062                                                                                                                                
|2063                                                                                                                                
|2075                                                                                                                                
|20                                                                                                                                  
|21                                                                                                                                  
|22                                                                                                                                  
|23                                                                                                                                  
|2421                                                                                                                                
|2436                                                                                                                                
|2493                                                                                                                                
|24                                                                                                                                  
|2511                                                                                                                                
|25                                                                                                                                  
|2611                                                                                                                                
|2621                                                                                                                                
|2631                                                                                                                                
|26                                                                                                                                  
|27                                                                                                                                  
|2812                                                                                                                                
|2813                                                                                                                                
|2816                                                                                                                                
|2819                                                                                                                                
|2821                                                                                                                                
|2822                                                                                                                                
|2823                                                                                                                                
|2824                                                                                                                                
|2861                                                                                                                                
|2865                                                                                                                                
|2869                                                                                                                                
|2873                                                                                                                                
|2874                                                                                                                                
|287                                                                                                                                 
|2895                                                                                                                                
|28                                                                                                                                  
|2911                                                                                                                                
|29                                                                                                                                  
|3011                                                                                                                                
|308                                                                                                                                 
|30                                                                                                                                  
|31                                                                                                                                  
|3211                                                                                                                                
|3221                                                                                                                                
|3229                                                                                                                                
|3231                                                                                                                                
|3241                                                                                                                                
|3274                                                                                                                                
|3296                                                                                                                                
|32                                                                                                                                  
|3312                                                                                                                                
|3313                                                                                                                                
|331                                                                                                                                 
|3321                                                                                                                                

See footnotes at end of table.

**Table 1. Number of Establishments and Weighted and Unweighted Percentages of
the Imputed Value of Shipments and Value Added (Continued)**

|             |                                               | **Value of Shipments**       | **Value Added**
|------------ | --------------------------------------------- | ---------------------------- | ---------------
|**SIC Code** | **Industry Groups****and Industry**           | **Number of Establishments** | **Percent**    
|3331         | Primary Copper                                | 3                            | W              
|3334         | Primary Aluminum                              | 3                            | W              
|3339         | Primary Nonferrous Metals, nec                | 38                           | 16.2           
|3353         | Aluminum Sheet, Plate, and Foil               | 12                           | 2.5            
|33           | Primary Metal Industries                      | 218                          | 11.0           
|34           | Fabricated Metal Products                     | 529                          | 8.4            
|357          | Computer and Office Equipment                 | 9                            | 0.2            
|35           | Balance of Industrial Machinery and Equipment | 545                          | 5.0            
|36           | Electronic and Other Electric Equipment       | 141                          | 1.5            
|3711         | Motor Vehicles and Car Bodies                 | 2                            | W              
|3714         | Motor Vehicle Parts and Accessories           | 36                           | 1.0            
|37           | Balance of Transportation Equipment           | 76                           | 1.1            
|3841         | Surgical and Medical Instruments              | 20                           | 1.7            
|38           | Balance of Instruments and Related Products   | 102                          | 2.4            
|39           | Miscellaneous Manufacturing Industries        | 141                          | 10.2           
|             | **Total**                                     | 6,284                        | 4.8            

W = Withheld to avoid disclosing data for individual establishments.

Source: Energy Information Administration, Office of Energy Markets and End Use, Energy
End Use and Integrated Statistics Division, Form EIA-846, "1994 Manufacturing Energy
Consumption Survey."

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