ADEQUACY OF DATA 



John JR. McGuire 

 A. A. Hasel 



The purpose of this part of the appendix is to 

 evaluate the major items of basic data in the Tim- 

 ber Resource Review, indicate their reUabiUty, 

 and point out their Hmitations. The discussion 

 generally follows the order in which the data ap- 

 pear in the body of the report. However, there 

 are some exceptions. For example, growth data 

 appear in the section Growth and Utilization, but 

 here they are discussed in connection with the data 

 on Forest Land and Timber. This is because 

 growth data, like forest area and timber volume 

 data, come from a common source — the Forest 

 Survey — and the adequacy of growth data depends 

 much upon the adequacy of the corresponding 

 area and volume data. 



Although procedures have an important bearing 

 on the reliability of the data, only a brief descrip- 

 tion of them is included here. In 1952 and 1953, 

 detailed working plans covering all phases of the 

 Timber Resource Review were widely circulated 

 and reviewed both in and outside the Forest Serv- 

 ice. These plans may be consulted in Forest Serv- 

 ice regional offices and experiment stations. In 

 addition, some procedures are described in other 

 sections of this report and in numerous Forest 

 Survey publications available in many libraries. 



OVERALL APPRAISAL 



In general, the most reliable data are those 

 presented as national and sectional estimates. 

 This is because the Timber Resource Review is 

 primarily an appraisal of the Nation's timber 

 situation as a whole and the data collected for it 

 are mainly in the detail needed for such a national 

 appraisal. In every case they are believed to be 

 adequate for this purpose. The regional estimates, 

 on the other hand, exhibit a wider range of reli- 

 ability. In one or two instances, such as the re- 

 gional statistics for the Plains Region, the data 

 may not be of sufficient reliability for a detailed 

 regional appraisal. But they are entirely adequate 

 for the main purpose intended here — to indicate 



the relative extent of regional variation in the 

 national timber situation. 



A greater attempt was made to obtain data by 

 States than in previous national appraisals of this 

 kind. Such data are useful to many in appraising 

 the State situation and in indicating the place of an 

 individual State in relation to other States and to 

 the Nation. However, the State data, which are 

 given mainly in the "Basic Statistics" part of this 

 appendix, are not a primary objective of the 

 Review, and they do not constitute a major part 

 of the analysis. Although many of the State 

 estimates are highly reliable, some are only 

 indicative. 



Possible Errors Are of Three Kinds 



In varying degree, all of the data are subject to 

 the possibility of error. Errors could have been 

 introduced through mistakes in classifying, meas- 

 uring, tabulating, and reporting; through faulty 

 judgment; or through the use of sampling proced- 

 ures. Errors may or may not be compensating. 

 Except for sampHng error, there is no way of 

 measuring them, but the chances of human error 

 were reduced as far as possible by following de- 

 tailed plans, by intensive training of personnel, 

 and by careful supervision and checking of the 

 work. Errors in judgment were minimized by 

 requij-ing some positive knowledge in support of 

 every regional estimate. However, in some esti- 

 mates, such as plantable area and growth impact, 

 judgment is more of a factor than in others because 

 complete quantitative information was not avail- 

 able. 



Sampling error accounts for errors that arise 

 from taking a sample rather than making a com- 

 plete inventory or measurement; it does not 

 include possible errors due to human mistakes or 

 faulty judgment. The samphng error of an 

 estimate is always given here in terms of one 

 standard error, i. e., the range about the estimate 

 within which the odds are 2 to 1 that the value 

 based on 100 percent coverage would fall. 



649 



