4_4_WP_4_06_ND_Model.pptx
- 1. MODEL, ASSUMPTIONS, ANALYSISOF VARIANCE
- 2. • Factors A(with a levels) and B (b levels) • Total of ab treatment combinations • The same number of replications per cell, n Nested Design A1 1 2 3 1 2 . n 1 2 . n 1 2 . n A2 1 2 3 1 2 . n 1 2 . n 1 2 . n A3 1 2 3 1 2 . n 1 2 . n 1 2 . n Factor B Replications
- 3. • Factor BLevel 1 in A1 is completely different from Factor B Level 1 in A2 and also in A3 • The levels of Factor B are nested within Factor A and there are n replicates within each combination. Nested Design A1 1 2 3 1 2 . n 1 2 . n 1 2 . n A2 1 2 3 1 2 . n 1 2 . n 1 2 . n A3 1 2 3 1 2 . n 1 2 . n 1 2 . n Factor B Replications
- 4. Example Hospital 1 W1 W2W3 1 2 . n 1 2 . n 1 2 . n W1 W2 W3 1 2 . n 1 2 . n 1 2 . n W1 W2 W3 1 2 . n 1 2 . n 1 2 . n Wards Hospital 2 Hospital 3 Patients Beds Locations Times Ward 1 in Hospital 1 is not the same level of the Ward factor as Ward 1 in Hospital 2 Ward – Random Effect Hospital – a random effect or fixed effect depending on contect
- 5. Example Area 1 V1 V2V3 1 2 . n 1 2 . n 1 2 . n V1 V2 V3 1 2 . n 1 2 . n 1 2 . n V1 V2 V3 1 2 . n 1 2 . n 1 2 . n Village Area 2 Area 3 Locations Times Person Household Village 1 in Area 1 is not the same level of the Village factor as Village 1 in Area 2 Village – Random Effect Area – could be a Fixed Effect or Random Effect depending on context
- 6. • The levelsof Factor B are completely crossed with Factor A - n replicates within each combination • Factor B Level 1 in A1 is exactly the same level as Factor B Level 1 in A2 - And all other levels of A Two Factor Design Data Layout Factor B Factor A 1 a 1 X111,X112,…, X11n Xa11,Xa12,…, Xa1n 2 X121,X122,…, X12n Xa21,Xa22,…, Xa2n Xij1,Xij2,…, Xijn b X1b1,X1b2,…, X1bn Xab1,Xab2,…, Xabn
- 7. Nested Design -degrees of freedom A1 1 2 3 𝑋11 A2 1 2 3 A3 1 2 3 Factor B • Combined factor has 𝑎𝑏 levels • 𝑎𝑏 − 1 degrees of freedom between the means • 𝑎 − 1 df associated with differences among the levels of A • 𝑎 𝑏 − 1 df associated with differences among B within A • 𝑛 replications within each combination used to estimate error • 𝑎𝑏 𝑛 − 1 df associated with the Error 𝐴1𝐵1 𝑋12 𝐴1𝐵2 𝑋13 𝐴1𝐵3 𝑋21 𝐴2𝐵1 𝑋22 𝐴2𝐵2 𝑋23 𝐴2𝐵3 𝑋31 𝐴3𝐵1 𝑋32 𝐴3𝐵2 𝑋33 𝐴3𝐵3 Combined levels Means Complete Factor
- 8. Effects Model 𝑋𝑖𝑗𝑘 =𝜇 + 𝜏𝑖𝑗 + 𝜖𝑖𝑗𝑘 = 𝜇 + 𝛼𝑖 + 𝛽𝑗 𝑖 + 𝜖𝑖𝑗𝑘 𝑖 = 1,2, … , 𝑎 𝑗 = 1,2, … , 𝑏 𝑘 = 1,2, … , 𝑛 The combined factor model is essentially the same model as for a Completely Randomised Design Differences among treatments plus an error term 𝜖𝑖𝑗𝑘 𝛼𝑖 main effect of level i of factor A 𝛽𝑗 𝑖 effect of level j of factor B nested within level i of factor A Treatment Effects written as a factorial structure. Effect of A Additional effect of B nested within A
- 9. • Factor B– the nested factor - generally defines a random effect, - e.g., randomly selected subjects or units - Assume 𝛽𝑗 𝑖 ~𝑁 0, 𝜎𝛽 2 independently of the errors, 𝜖𝑖𝑗𝑘. • Factor A - may be either a fixed effect with 𝛼𝑖 = 0 as constraint - or random effect with 𝛼𝑖~𝑁 0, 𝜎𝛼 2 assumed. • Therefore, ND based experiments will be mostly mixed effects (type III) or random effects (type II) models • Errors, 𝜖𝑖𝑗𝑘, normally distributed and independent with constant variance; additive terms Assumptions
- 10. Hypotheses • Fixed Effect •Factor A • 𝐻0: 𝛼𝑖 = 0, for all i • 𝐻1: 𝛼𝑖 ≠ 0, for at least one i • Factor B • 𝐻0: 𝛽𝑗 𝑖 = 0, for all i, j • 𝐻1: 𝛽𝑗 𝑖 ≠ 0, for at least one i,j • Random Effect • • Factor A • 𝐻0: 𝜎𝛼 2 = 0 • 𝐻1: 𝜎𝛼 2 > 0 • Factor B • 𝐻0: 𝜎𝛽 2 = 0 • 𝐻1: 𝜎𝛽 2 > 0
- 11. Source df SSMS Factor A 𝑎 − 1 SSA 𝑀𝑆𝐴 = 𝑆𝑆𝐴 𝑎 − 1 Factor B (within A) 𝑎 𝑏 − 1 SSB 𝐴 𝑀𝑆𝐵 𝐴 = SSB 𝐴 𝑎 𝑏 − 1 Error (Residual) 𝑎𝑏 𝑛 − 1 SSE = 𝑆𝑆𝑇 − 𝑆𝑆𝐴 − SSB 𝐴 𝑀𝑆𝐸 = 𝑆𝑆𝐸 𝑎𝑏 𝑛 − 1 Total 𝑎𝑏𝑛 − 1 𝑆𝑆𝑇 Anova for 2 factor Nested model
- 12. Source df MSF EMS Factor A 𝑎 − 1 𝑀𝑆𝐴 = 𝑆𝑆𝐴 𝑎 − 1 𝑀𝑆𝐴 𝑀𝑆𝐵 𝐴 𝜎2 + 𝑛𝜎𝛽 2 + 𝑏𝑛𝜎𝛼 2 Factor B (within A) 𝑎 𝑏 − 1 𝑀𝑆𝐵 𝐴 = SSB 𝐴 𝑎 𝑏 − 1 𝑀𝑆𝐵 𝐴 𝑀𝑆𝐸 𝜎2 + 𝑛𝜎𝛽 2 Error (Residual) 𝑎𝑏 𝑛 − 1 𝑀𝑆𝐸 = 𝑆𝑆𝐸 𝑎𝑏 𝑛 − 1 𝜎2 Total 𝑎𝑏𝑛 − 1 F tests B Random Effect Factor A can be Fixed or Random
- 13. Source df MSF EMS Factor A 𝑎 − 1 𝑀𝑆𝐴 = 𝑆𝑆𝐴 𝑎 − 1 𝑀𝑆𝐴 𝑀𝑆𝐸 𝜎2 + 𝑏𝑛𝜎𝛼 2 Factor B (within A) 𝑎 𝑏 − 1 𝑀𝑆𝐵 𝐴 = SSB 𝐴 𝑎 𝑏 − 1 𝑀𝑆𝐵 𝐴 𝑀𝑆𝐸 𝜎2 + 𝑛𝜎𝛽 2 Error (Residual) 𝑎𝑏 𝑛 − 1 𝑀𝑆𝐸 = 𝑆𝑆𝐸 𝑎𝑏 𝑛 − 1 𝜎2 Total 𝑎𝑏𝑛 − 1 F tests B Fixed Effect 𝜎𝛽 2 = 𝑖𝑗 𝛽𝑗 𝑖 2 Factor A can be Fixed or Random