Directions and Explanations is also divided exceptionally into five "Parts" for considering separately 

 five subcategories of the major category of information represented in Field E. 



Fields G-l and G-2 have been discussed in the Key as a unit, since the same general type of 

 information is coded in both fields and symbols used for coding in both fields are from the identical 

 list in the Code. Distinguishing the uses of the two fields is also facilitated by discussing the two 

 together. For the same reason, Fields H-l and H-2 are described as a unit, as well as Fields S-l, 

 S-2, and S-3. 



Discussing Fields M and N as a unit is not due to their having an identical list of code symbols, 

 but due to both fields being concerned with a similar type of information. The uses of the two fields 

 can be distinguished more easily by considering them together. For the same reason, the descriptions 

 of Fields W, X, and Y are presented essentially as a unit, though, like Fields M and N, each of Fields 

 W, X, and Y has a different set of items and symbols in the Code. 



Each of Fields T-l, T-2, and T-3 is discussed individually, even though all three deal generally 

 with only a single category of information. Nevertheless, it has been convenient to introduce these 

 three fields by a separate discussion of Field T, embodying explanation of the general objective shared 

 by the three fields and general distinction in their use. 



In all symbols of the Code to which reference is made in the Key, the capital letter O is indi- 

 cated by the special symbol "0" to give it obvious distinction from the numerical zero. 



For convenience, the term "double coding" has been used in the Key and Code with a limited 

 definition; therefore, two symbols being entered in one column in one code line does not necessarily 

 represent "double coding". The definition assigned to the term hinges on the evaluation of test results, 

 ordinarily of two or more tests; in these tests, some condition of the test method differs (ordinarily, 

 only one condition is involved), yet the test results are so nearly the same that the code evaluation of 

 the biological response in both or all tests is by the identical symbol in Field Y. Both or all of such 

 tests might be coded by a single code line in which the field coding the variable test condition (e. g. , 

 dose size, inoculum size, or route of administration) would have "double coded" the symbols for both 

 or all of the variations of that condition (e. g. , the range of doses or the various inoculum sizes or the 

 various administration routes [Field M, Q, or S], giving test result evaluations indistinguishable by 

 code in Field Y). Thus, "double coding" refers to the use of two symbols in one column representing 

 variation in a single category of information. 



In certain fields, symbols are provided for two different categories of information (e.g. , Fields 

 A, B, F, G, O, W) and, in these fields, the symbols of one information catetory (Symbol of Field A, 

 e. g. ) can be entered in the same column of the same code line as symbols of the other category (symbols 

 other than Symbol of Field A, e.g. ), whenever information of both categories is available for the test. 

 These two entries in a single column, however, do not represent "double coding", as defined above. 



In either case ("double coding" of the same category of information from two or more tests or 

 the use of two or more symbols for two different categories of information in one test), the multiple 

 coding of the column is punched on the same IBM card in that column. 



However, fields for which the CBCC has established separate IBM punched card files ("filing 

 fields", Fields D, E. H, I, J, T-2, and T-3) are never "double coded". Even if this were permitted, 

 instructions would be given to punch two IBM cards, identical except in the field double coded on the 

 Code Sheet. The reason for this is simply that a card is needed for each entry in one of these fields, 

 in order to have the entry filed in the proper category. 



The free use of underscoring in the Key perhaps needs some clarification. For some readers 

 the underscoring may be distracting, but in general, the emphasis placed on a given word or phrase 

 by an underscore has seemed to assist far more than to deter in extracting the intended meaning from 

 explanations which have been sometimes difficult and necessarily complex. 



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