Strip Plot Design

Strip Plots Experimental units for factors are row strips (row factor) and column strips (column factor) Convenient design for two-factor agricultural experiments Alternative to split-plot design when split-plots are not practical as experimental units for either factor

Strip Plot Alternatives The design requires replication of both row and column strips Just as with split plot design, we can replicate across blocks, or replicate within a single block (i.e., plot)

Strip Plot Model I Yandell Model S=set. Draw diagram

Strip Plot I Discussion In Yandell’s model, sk indexes set , which actually functions as a block It’s surprising that Yandell doesn’t present nested strip plot errors Strip plot errors are really just block (or set) by treatment interactions

Strip Plot Model II It may be more proper to consider the model as: Draw layout (assume s=1)

Strip Plot Model III Another version of the strip plot model (consistent with Yandell’s split plot design):

Strip Plot Design I & II ANOVA

Strip Plot Design I & II ANOVA (cont)

Strip Plot Design III ANOVA

Strip Plot Design III ANOVA (cont)

Pairwise Contrasts Main effects contrast estimates are straightforward to compute, though their standard errors vary: E.g. Write out ybar(i..), E(ybar(i..)), V(ybar(i..))

Strip Plot Design LSMEANS Use, e.g,. /E=A*S in LSMEANS to assign correct error term in PROC GLM Standard interaction contrast estimates are straightforward as well We did not discuss this, but split plot interaction contrasts involving cell means could involve comparisons across subplots, or plots or both. Think how messy some of these comparisons could be based on the previous slide’s calculations

Strip Plot Design LSMEANS (cont) This same problem occurs for interaction contrasts in the strip plot design Care must be taken when estimating these contrasts Yandell somewhat overstates severity of this problem

Strip Plot Example Strip plot design with Variety (DPL 454BR, DPL 555BR, ST 5599BR, PHY 375WRF) as row factor and Fungicide (Ridomil, Terraclor, Quadras) as column factor Fields are block Nested row and column strip plots Response is yield (cotton lint in pounds/acre) Run SAS code. The model is a hybrid of the designs we listed.