ISM 6137 Ch 2 Part 11Chapter 5Chapter 2Describing the Distribution of a Single VariablePart 1 Types of variables, Central Tendency 2-2a Populations and SamplesA population includes all of the entities of interest in a study (people, households, machines, etc.).ExamplesAll potential voters in a presidential electionAll subscribers to cable televisionAll invoices submitted for Medicare reimbursement by nursing homesA sampleis a subset of the population, often randomly chosen and preferably representative of the population as a whole.2-2b Data Sets, Variables, and ObservationsAdata set is usually a rectangular array of data, with variables in columns and observations in rows. A variable(or fieldor attribute) is a characteristic of members of a population, such as height, gender, or salary. An observation(or caseor record) is a list of all variable values for a single member of a population.Observation/record 2Observation/record 3Observation/record 4Observation/record 1Variable/field 1Variable/field 2Variable/field 3Variable/field 42-2c Types of Data(slide 1 of 5)A variable is numericalif meaningful arithmetic can be performed on it. Otherwise, the variable is categorical.There is also a third data type, a datevariable.Excel®stores dates as numbers, but dates are treated differently from typical numbers.A categorical variable is ordinalif there is a natural ordering of its possible values.If there is no natural ordering, it is nominal.1234
ISM 6137 Ch 2 Part 12Types of Data(slide 2 of 5)Categorical variables can be coded numerically.A dummy variable is a 0–1 coded variable for a specific category.It is coded as 1 for all observations in that category and 0 for all observations not in that category.A binned(ordiscretized)variablecorresponds to a numerical variable that has been categorized into discrete categories.