MEASUREMENT SCALES

Measurement scales are used to categorize and/or quantify variables. This lesson describes the four scales of measurement that are commonly used in statistical analysis: nominal, ordinal, interval, and ratio scales.

Properties of Measurement Scales

Each scale of measurement satisfies one or more of the following properties of measurement.

• Identity. Each value on the measurement scale has a unique meaning.
  
• Magnitude. Values on the measurement scale have an ordered relationship to one another. That is, some values are larger and some are smaller.
  
• Equal intervals. Scale units along the scale are equal to one another. This means, for example, that the difference between 1 and 2 would be equal to the difference between 19 and 20.
  
• A minimum value of zero. The scale has a true zero point, below which no values exist.

Nominal Scale of Measurement

The nominal scale of measurement only satisfies the identity property of measurement. Values assigned to variables represent a descriptive category, but have no inherent numerical value with respect to magnitude.

Gender is an example of a variable that is measured on a nominal scale. Individuals may be classified as "male" or "female", but neither value represents more or less "gender" than the other. Religion and political affiliation are other examples of variables that are normally measured on a nominal scale.

Ordinal Scale of Measurement

The ordinal scale has the property of both identity and magnitude. Each value on the ordinal scale has a unique meaning, and it has an ordered relationship to every other value on the scale.

An example of an ordinal scale in action would be the results of a horse race, reported as "win", "place", and "show". We know the rank order in which horses finished the race. The horse that won finished ahead of the horse that placed, and the horse that placed finished ahead of the horse that showed. However, we cannot tell from this ordinal scale whether it was a close race or whether the winning horse won by a mile.

Interval Scale of Measurement

The interval scale of measurement has the properties of identity, magnitude, and equal intervals.

A perfect example of an interval scale is the Fahrenheit scale to measure temperature. The scale is made up of equal temperature units, so that the difference between 40 and 50 degrees Fahrenheit is equal to the difference between 50 and 60 degrees Fahrenheit.

With an interval scale, you know not only whether different values are bigger or smaller, you also know how much bigger or smaller they are. For example, suppose it is 60 degrees Fahrenheit on Monday and 70 degrees on Tuesday. You know not only that it was hotter on Tuesday, you also know that it was 10 degrees hotter.

Ratio Scale of Measurement

The ratio scale of measurement satisfies all four of the properties of measurement: identity, magnitude, equal intervals, and a minimum value of zero.

The weight of an object would be an example of a ratio scale. Each value on the weight scale has a unique meaning, weights can be rank ordered, units along the weight scale are equal to one another, and the scale has a minimum value of zero.

Weight scales have a minimum value of zero because objects at rest can be weightless, but they cannot have negative weight.

Different Types of Evaluation

Once you pinpoint the reason for conducting your evaluation and the target population, you can better determine the most appropriate type of evaluation. This section describes the five major types of evaluations and the appropriate circumstances for their uses.

  

Click on the links below to view information on types of evaluation 

• Formative
• Summative
• Process
• Outcomes
• Impact

Evaluation Type	Definition	Uses	Examples
Formative	Evaluates a program during  development in order to make early improvements Helps to refine or improve program	When starting a new program To assist in the early phases of program development	How well is the program being delivered? What strategies can we use to improve this program?
Summative	Provides information on program effectiveness Conducted after the completion of the program design	To help decide whether to continue or end a program  To help determine whether a program should be expanded to other locations	Should this program continue to be funded? Should we expand these services to all other after-school programs in the community?
Process	Determines if specific program strategies were implemented as planned Focuses on program implementation	To determine why an established program has changed over time To address inefficiencies in program delivery of services To accurately portray to outside parties program operations (e.g., for replication elsewhere)	Did your program meet its goals for recruitment of program participants?  Did participants receive the specified number of service hours?
Outcomes	Focuses on the changes in comprehension, attitudes, behaviors, and practices that result from programs activities Can include both short and long term results	To decide whether program/activity affect participants outcomes To establish and measure clear benefits of the program	Did your participants report the desired changes after completing a program cycle?  What are the short or long term results observed among (or reported by) participants?
Impact	Focuses on long term, sustained changes as a result of the program activities, both positive/negative and intended/unintended	To influence policy To see impact in longitudinal studies with comparison groups	What changes in your program participants’ behaviors are attributable to your program?  What effects would program participants miss out on without this program?

Diagnostic assessment is a type of assessment which examines what a student knows and can do prior to a learning program being implemented. Assessment of students' skills and knowledge upon entry to the program provides a baseline against which to assess progress.

prognosis

 

Definition

 

Assessment or prediction (in the sense of a best educated guess) of the future course of the development, outcome, or progress of a condition or phenomenon, based on a careful diagnosis of the case. It is an attempt to anticipate probable consequences, and the price of their effects in terms of money, disruption, discomfort, pain, etc. Search for an effective remedy is futile without an effective prognosis.