FIELDS W, X, and Y 



Columns 68; 69 and 



70; and 71 



has been specially scaled so that a cumulative normal distribution curve assumes the form of a straight 

 line. (The horizontal scale of this paper is arithmetic. ) The paper is frequently used to indicate how 

 nearly a given set of test results (involving distribution of response within a group of individuals) 

 approaches or deviates from the "normal" distribution curve by observing how the data plotted on the 

 paper deviate from a straight line. 



A modification of this probability graph paper consists of applying a logarithmic horizontal 

 scale rather than an arithmetic one. This paper is referred to as logarithmic probability paper and it 

 is employed for asymmetrical distribution curves when this asymmetry is due to the peak of the distri- 

 bution curve occurring to the left (the curve being described as "skewed to the right"), illustrated in 

 Figure A below. 



For biological data in general, the CBCC has used a logarithmic scale on ordinary probability 

 paper. (The horizontal scale of this paper is ruled as an arithmetic scale, but on this arithmetic scale 

 are placed the consecutive ranges of dosage scales of Field M or N or of the time scales of Field P or 

 U, which it will be noted are logarithmic. Observe the code scales of Fields M, N, P, and U. ) The 

 following example (a table of simple data and two figures) illustrates the dosage/percentage-organisms- 

 responding data and the distribution curves depicting these data (response distribution curve, Figure A, 

 and cumulative response distribution curve, Figure B). 



Dose causing 

 the response 

 (or dose causing 

 death) 



2. 5 mg 



5. mg 



8. mg 



12. mg 



15. mg 



Percentage of individuals 

 showing a specific response 

 intensity (or percentage of 

 individuals killed) 



10% show response 



an additional 32% show response 



an additional 28% show response 



an additional 20% show response 



the final 10% show response 



Cumulative percentage 

 of individuals 



a total of 10% respond 

 a total of 42% respond 

 a total of 70% respond 

 a total of 90% respond 

 a total of 100% respond 



5 10 15 20 25 

 Figure A 



100 

 -75 

 -50 



25 







/ 



A 



5 10 15 20 25 

 Figure B 



100 

 75 

 50 

 25 



It is the cumulative distribution curve, Figure B, or any points thereon, that can be placed on 

 the logarithmic probability chart used by the CBCC, referred to hereafter in this division (and else- 

 where in the Code and Key) as the Log-Probit Grid or merely as the Grid. 



For any given test compound, it should be understood that all points on any one cumulative 

 distribution curve (Figure B) must be represented by a single code evaluation in Field Y. This is also 

 true of this curve when it is plotted on the Grid and when it therefore is transformed to more nearly 

 approach a straight line. In other words, any data placed on the Grid represent a cumulative distri- 

 bution curve (transformed to a straight line) or (if none of the doses administered cause the given 

 response intensity in 100% of the organisms tested), it represents a part of the total cumulative distri- 

 bution curve and it is this curve's position on the Grid (or the position, on the Grid, of that demonstrated 

 fragment of the curve) that must be the basis for an evaluation of the compound's potency for affecting 

 all Individuals of the test organism species or strain. 



- 206 - 



