Foundations I Basic Concepts & Definitions

IVPPSSSlide #2 What are the Following Items? I V P S ndividual - items that we will observe ariable - characteristic of the individuals observed opulation - all of the individuals of interest arameter - summary (numerical or graphical) of the variable for the population ample - portion of the population we actually examine tatistic - summary of the variable for the individuals in the sample

IVPPSSSlide #3 The Sustainability Coordinator surveyed 147 randomly selected Northland students in Fall, 2013 to determine (among other things) the average number of miles that Northland students drove per week. A climatologist wanted to determine the average amount of snow for December in Duluth, MN. She selected a random sample of 35 Decembers (from recorded history) and recorded the total snowfall for each. Example IVPPSS

IVPPSSSlide #4 Example IVPPSS 215 rabbit (Oryctolagus cuniculus L.) carcasses were examined for signs of myxomatosis 1 on Bridgets Farm (Hampshire, southern England) during a period when the density of fleas 2 had been substantially reduced with an insecticide. Primary interest was in the proportion of carcasses that exhibited signs of myxomatosis. 3 1 A disease causing drastic declines in wild rabbit populations 2 The primary vector for the myxomatosis disease 3 Trout et al. (J. Appl. Ecol :79-686)

IVPPSSSlide #5 Important Relationships What describes this relationship? ParameterPopulation Statistic Sample ParameterPopulation Statistic Sample Summarization Representation or Estimation

Variable TypesSlide #6 Variable Types Quantitative (Measurement / Counts / Numbers) –Continuous a potential value exists between all pairs of values –Discrete a potential value does not exist between all pairs of values typically (but not always) counts of things Categorical (Qualitative).. group membership –Ordinal a natural order exists among the categories –Nominal no natural order exists among the categories What are the two main types of variables (i.e., first level of splitting)? How do they differ? What are the two main types of quantitative variables? How do they differ? What are the two main types of categorical variables? How do they differ?

Variable TypesSlide #7 … “miles driven per week”? … “type of vehicle (e.g., SUV, …)”? … “signs of myxomatosis or not (Y/N)”? … “number of fleas found per rabbit”? … “relative health of the rabbit (poor, good, excellent)”? … “species of rabbit”? … “number of correct answers”? Example Variable Types What type of variable is … Name a variable, from your own example, for each variable type.

Important Distinction What are the possible answers for the following two question types? What type of variable is blah-blah-blah? What type of variability explains the fact that yada- yada-yada? Foundations ISlide #8