Pre-Quiz (work with a partner) Low temp High temp E. C. Enders, D. Boisclair, P. Boily, P. Magnan 2006 Med. temp Explain in plain English what this figure is showing. Why might metabolic rate change with temperature? What would you predict for a snake versus a mouse? How many individuals would we have to sample to estimate the respiration of fish in a lab tank? In a river? Explain your reasoning. Fish Metabolic Rates

Experimental Setup How would you design an experiment to test the relationship between temperature and metabolic rate? Work in groups to design an experiment Hypothesis: predictions Treatments The experimental system: Fish held at 2 different temperatures (10 & 20 o C) Respiration measured by counting operculum beats Test chambers Water for testing at the 2 temperatures Replication Specific Protocol

Types of Statistical Designs 1. Observational Study: Any study where we simply observe a response on a number of observational units with no manipulation from the researcher. Confound and bias Scope of inference 2. Controlled Experiment: Experimental units are randomly assigned to groups OR randomly selected from a population and a response is observed. Scope of inference

Principles of Experimental Design 1. Comparison: Any experiment must have at least 2 treatment groups. The goal is then to compare the treatment groups in terms of a response. Control group – is this necessary? 2. Randomization: Experimental units are randomly assigned to groups. Is randomization necessary? Why? Sources of bias

Principles of Experimental Design 3. Replication: Replication occurs when multiple experimental units receive the same treatment. Purpose of replication? Sample size 4. Blindness: When possible, the experimental units (and sometimes the researchers) should be blind to which treatment group they belong. Should we tell the fish? Placebo effect