Foundations I

Basic Concepts & Definitions

IVPPSS Slide #2

What are the Following Items?• I• V• P• P

• S

• S

ndividual - items that we will observeariable - characteristic of the individuals observedopulation - all of the individuals of interestarameter - summary (numerical or graphical) of the variable for the populationample - portion of the population we actually examinetatistic - summary of the variable for the individuals in the sample

IVPPSS Slide #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

IVPPSS Slide #4

Example IVPPSS215 rabbit (Oryctolagus cuniculus L.) carcasses were examined for signs of myxomatosis1 on Bridgets Farm (Hampshire, southern England) during a period when the density of fleas2 had been substantially reduced with an insecticide. Primary interest was in the proportion of carcasses that exhibited signs of myxomatosis.3

1A disease causing drastic declines in wild rabbit populations2The primary vector for the myxomatosis disease3Trout et al. (J. Appl. Ecol. 1992. 29:79-686)

IVPPSS Slide #5

Important RelationshipsWhat describes this relationship?

What describes this relationship?

Parameter Population

Statistic Sample

Parameter Population

Statistic Sample

Summarization

Representationor

Estimation

Variable Types Slide #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 Types Slide #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 TypesWhat type of variable is …

Name a variable, from your own example, for each variable type.

Foundations I

Important DistinctionWhat 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?

Slide #8