There are five components to an experiment: hypothesis, experimental design,
experimental execution ... 2006. Experimental Design for the Life Sciences.
Research Design
There are five components to an experiment: hypothesis, experimental design, experimental execution, statistical analysis, and interpretation.
Ruxton, G.D. and N. Colegrave. 2006. Experimental Design for the Life Sciences.
IMPORTANT ISSUES IN RESEARCH DESIGN •Common Sense •Observational vs. Experimental •Snapshot vs. Trajectory Studies •Manipulative vs. Mensurative Experiments •Press (resistance) vs. Pulse (resilence) •Replication •Power analyses •Independence •Confounding factors •Pseudoreplication •Spatial and temporal scales •Frequently used experimental designs
POWER
Type II Error H0 True
H1 True
Type II Error
Statistical Power H0 False H0 True Power
Type II Error
title 'Sample size determination: Standard deviation known'; proc power; twosamplemeans sides = 2 alpha = 0.05 groupmeans = .03 | .025 .02 .015 stddev = .008 groupweights = 1 | 1 power = 0.8 ntotal = .; plot y=power min=0.5 max=0.95; run; pwr.t.test(n = , d = 0.625, sig.level = 0.05, power = 0.8, type = c("two.sample")) pwr.t.test(n = , d = 1.25, sig.level = 0.05, power = 0.8, type = c("two.sample")) pwr.t.test(n = , d = 1.875, sig.level = 0.05, power = 0.8, type = c("two.sample"))
Independence, confounding factors, scale, and other issues
• Replication— reduces random variation or error! • Randomization —eliminates bias and environmental variation.
Nondemonic intrusion is defined as the impingement of chance events on an experiment in progress. As a safeguard against both it and preexisting gradients, interspersion of treatments is argued to be an obligatory feature of good design.
Pseudoreplication
Pseudoreplication
Pseudoreplication
Pseudoreplication
Pseudoreplication
When is pseudoreplication a pseudoissue?
When is pseudoreplication a pseudoissue? •When pseudoreplicates are not treated as replicates. •When the inference is meant to be restricted. •BACI designs. •See also Oksanen
Blocking
Randomized Complete Blocks Design I
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Each pen has all four diets represented
