Section 1.3 | Variables and Measurement Flashcards
Define:
constructs
Define:
operational definition
An operational definition identifies a measurement procedure (a set of operations) for measuring an external behaviour and uses the resulting measurements as a definition and a measurement of a hypothetical construct. Note that an operational definition has two components. First, it describes a set of operations for measuring a construct. Second, it defines the contrust in terms of the resulting measurements.
Define:
discrete variable
A discrete variable consists of separate, indivisible categories. No values can exist between two neighboring categories.
- Commonly restricted to whole, countable numbers.
- A discrete variable may also consist of observations that differ qualitatively; e.g. people can be classified by their occupation (nurse, teacher, lawyer, etc.).
Define:
continuous variable
For a continuous variable, there are an infinite number of possible values that fall between any two observed values. A continuous variable is divisible into an infinite number of fractional parts.
- It is almost impossible for two individuals to obtain identical scores because a continuous variable has an infinite number of possible values.
- When measuring a continuous variable, each measurement category is actually an interval that must be defined by boundaries. For example, if two people both claim to weigh 150 lbs, one could weigh 149.6 lbs while the other weights 150.3 lbs.
What are real limits, and the upper real limit and lower real limit?
Real limits are the boundaries of intervals for scores that are represented on a continuous number line. The real limit separating two adjeacent scores is located exactly halfway between the scores. Each score has two real limits. The upper real limit is at the top of the interval, and the lower real limit is at the bottom.
- The concept of real limits applies to any measurement of a continuous variable, even when the score categories are not whole numbers.
- Remember that real limits are always halfway between adjacent categories.
How can you tell if a variable is continuous or discrete?
The terms continuous and discrete apply to the variables that are being measured and not to the scores that are obtained from the measurment. For example, measuring people’s heights to the nearest inch produces scores of 60, 61, 62, and so on. Although the scores may appear to be discrete numbers, the underlying variable is continuous.
The key to determining whether a variable is continuous or discrete is that a continuous variable can be divided into any number of fractional parts. In other words, you are free to choose the degree of precision or the number of categories for measuring a variable.
What is a scale of measurement? What are the four different scales of measurement?
The categories we use to measure a variable make up a scale of measurement, and the relationships between the categories determine different types of scales. The differences between these scales recognize that some measurements are more appropriate for statistical procedures than others. For example, you could classify height as either short, medium, or tall, but it would not tell you how tall anyone is or let you determine an average.
The four different types of measurement are the nominal scale, ordinal scale, interval scale, and ratio scale.
Define:
nominal scale
A nominal scale consists of a set of categories that have different names. Measurements on a nominal scale label and categorize observations, but do not make any quantitative distinctions between observations.
- Categories on a nominal scale are not quantitative values, but they are occaisionally represented by numbers. For example, Room 109 is not necessarily bigger than Room 100, and certainly not 9 points bigger.
Define:
ordinal scale
An ordinal scale consits of a set of categories that are organized in an ordered sequence. Measurements on an ordinal scale rank observations in terms of size or magnitude.
- Since the categories form an ordered sequence, there is a directional relationship between categories.
- However, ordinal measurements do not allow you to determine the size of the difference between two individuals.
Define:
interval scale
An interval scale consits of ordered categories that are all intervals of exactly the same size. Equal differences between numbers on a scale reflect equal differences in magnitude. However, the zero point on an interval scale is arbitrary and does not indicate a zero amount of the variable being measured.
Define:
ratio scale
A ratio scale is an interval scale with the additional feature of an absolute zero point. With a ratio scale, ratios of numbers do reflect ratios of magnitude.
