A Target-Control Analysis of Wheat Yield Data for the North Dakota Cloud Modification Project Region

Paul L Smith, L Ronald Johnson, David L Priegnitz, Paul W Mielke, Jr.


A combined historical/target-control analysis of annual wheat yield data for western North Dakota provides indications of possible seeding effects in the target areas of the North Dakota Cloud Modification Project (NDCMP). The basic analysis procedure comparing post-1975 seeded-period data with pre-1961 non-seeded data gives an estimated yield increase of about 6%, relative to the control area, during the NDCMP operational period. However, the statistical (P-value) indications of the significance of the difference are somewhat equivocal. The historical increase in yields due to improvements in agricultural technology apparently contributes to this difficulty, but an attempt to resolve the issue by redefining the historical reference period to reduce the time gap was unsuccessful.

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