68 



MISSOURI AGR. EXP. STA. RESEARCH BULLETIN 49 



ing error by this practice when the tested varieties are quite different 

 in habit from the check variety. 



The use of an unsuitable check variety not only increases the 

 margin of error, but it may cause very deceptive comparative results. 

 For example, the average yields of the Kherson strains 0155 and 0157, 

 unadjusted and adjusted according to the yields of both check va- 

 rieties, are shown below : 



The 17 per cent advantage in yield of strain 0157 is increased to 

 27 per cent by the Kherson adjustment, and since the variability of 

 the replicate yields is reduced by the adjustment we may fairly as- 

 sume that the latter is the more reliable figure. But when the Red 

 Rustproof check is used for adjusting yields, the advantage of strain 

 0157 disappears entirely. The inaccuracy of the yields adjusted by 

 Red Rustproof is indicated by the increase in plot variability result- 

 ing from this adjustment. Thus the adjustment of yields by means 

 of check plots may mask considerable differences in yields between the 

 varieties under test. 



Although Kherson and Red Rustproof are decidedly different in 

 type, both are commonly grown in Missouri, and both have been used 

 frequently here as check varieties in oats variety tests. It is interesting 



TABLE 39. RELATIVE VARIABILITY OF ACTUAL AND ADJUSTED YIELDS OF KHERSON 



AND RED RUSTPROOF OATS, EACH IN 120 DISTRIBUTED PLOTS. 



Oats Variety and Strain Tests 1921. 



