IV. RINGS 



During and following the processes of cross-identification and 

 dating, described in the previous volume, the best ring records are 

 picked out by a form of selection, first between the different trees of 

 the group, and second between different parts of each tree record. 



SELECTION IN GROUP 



During cross-identification it is very easy to see which specimens 

 conform best to the group type and which ones conform so little as to 

 be discordant, for in all the groups used a group type is evident. It 

 becomes, then, easy to recognize any specimen which for some reason 

 or other, perhaps a fire injury or a different water-supply, does not 

 agree with its group. Such specimens are obviously so far from the 

 average that probable errors are diminished by their omission and 

 their values are not included in the group average. Such individuals 

 are usually very few in number, in the majority of groups none at all, 

 and they include of course the ones which can not be cross-identified. 



MEAN CONFORMITY 



In judging whether any tree should be retained in the group a 

 criterion called "mean conformity" has been very extensively used. 

 It is the agreement which any individual shows to its group or type. 

 In effect, it is an added weight given to individual specimens which 

 have the best support from other members of the group. 



Quantitative conformity — An actual numerical value of this con- 

 formity could be derived by mathematics (by mean residuals from 

 group averages), but it would be a long process and the results at the 

 present stage would not be worth the labor; for after familiarity is 

 reached a conformity coefficient can be estimated, as in a multitude 

 of different scientific observations. However, in connection with the 

 selection of best sequoia records for comparison with Arizona pines, 

 a quantitative value was reached in a practical way. The Arizona 

 variations were kept fresh in mind as each sequoia record was reviewed. 

 The number of Arizona features found in each sequoia for each of the 

 last five centuries was carefully recorded and the total placed against 

 each sequoia as its weight or conformity. Those having the best con- 

 formity were then selected for certain comparison problems. This is a 

 good practical method. Other selections have not been made on so 

 large a scale and did not need such formal organization, but nearly all 

 have been based on some modification of this process. 



Weighted means — After mean conformity of each member of a 

 group has been obtained, it may be used simply to exclude poor 

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