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Experimental design and analysis

Experimental design and analysis. BACI environmental sampling designs. Basic BACI designs . Impact monitoring Single Impact & Control areas Some sub-samples? Sampled through time Before & After periods Times within each period. BACI test .

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Experimental design and analysis

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  1. Experimental design and analysis BACI environmental sampling designs

  2. Basic BACI designs • Impact monitoring • Single Impact & Control areas • Some sub-samples? • Sampled through time • Before & After periods • Times within each period

  3. BACI test • Did the Impact area change, relative to the Control area, after the particular human activity occurred? • Complex analysis or t-test

  4. Impact Control Time Time

  5. Impact Control Procedure • Plot values for each location through time • Calculate di = Ci - Ii for each time • Compare d values between groups (Before & After) - ANOVA or t-test. Time

  6. Impact Control d d Time Time

  7. d - values Time Time

  8. BACI as a partly-nested design

  9. Before After Control Impact 1 2 3 4 5 6 Sampling Times

  10. Before After Control Impact 1 2 3 4 5 6 “Plots”

  11. 1 2 3 4 5 6 Factor A (Periods) Factor C (C-I) “Plots”

  12. The linear model • Times (T) nested within Before & After (BA) • Crossed with Control-Impact (CI) • Time random, but BA and CI are fixed • DV =  + BA +T(BA) + CI + BA*CI • No replication (no Times x CI interaction) • Power depends on # of times

  13. Before After Sites Control Impact 1 2 3 4 5 6 Times 1 2 3 4 5

  14. MBACI • Now four factors: • BA - fixed • Times within Before & After - fixed?? • CI - fixed • Sites within Control & Impact - random • DV=  + BA + T(BA) + CI + S(CI) + BA*CI + CI*T(BA) + BA*S(CI) • Test BA*CI using BA*S(CI) as denominator

  15. MBACI • Power depends on # of sites • Because test is made with BA x sites, critical assumptions are about how the BA changes occur at the “replicate” sites • Are these changes normal, homogeneous variances, etc?

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