Concerning rating scales as systems of educational marks, see more articles about education in different countries (named "Education in ..."), for example, Education in Ukraine. Concerning rating scales used in the practice of medicine, see articles about diagnoses, for example, Major depressive disorder.
A rating scale is a set of categories designed to elicit information about a quantitative or a qualitative attribute. In the social sciences, particularly psychology, common examples are the Likert response scale and 1-10 rating scales in which a person selects the number that is considered to reflect the perceived quality of a product.
Background
A rating scale is a method that requires the rater to assign a value, sometimes numeric, to the rated object, as a measure of some rated attribute
Types of rating scales
All rating scales can be classified into one of these types: Numeric Rating Scale (NRS) Verbal Rating Scale (VRS) Visual Analogue Scale (VAS) Likert Graphic rating scale Descriptive graphic rating scale
Some data are measured at the ordinal level. Numbers indicate the relative position of items, but not the magnitude of difference. Attitude and opinion scales are usually ordinal; one example is a Likert response scale:
Statement e.g. "I could not live without my computer". Response options Strongly disagree Disagree Neutral Agree Strongly agree
Some data are measured at the interval level. Numbers indicate the magnitude of difference between items, but there is no absolute zero point. A good example is a Fahrenheit/Celsius temperature scale where the differences between numbers matter, but placement of zero does not.
Some data are measured at the ratio level. Numbers indicate magnitude of difference and there is a fixed zero point. Ratios can be calculated. Examples include age, income, price, costs, sales revenue, sales volume and market share.
More than one rating scale question is required to measure an attitude or perception due to the requirement for statistical comparisons between the categories in the polytomous Rasch model for ordered categories. In terms of Classical test theory, more than one question is required to obtain an index of internal reliability such as Cronbach's alpha, which is a basic criterion for assessing the effectiveness of a rating scale and, more generally, a psychometric instrument.
Rating scales used online
Rating scales are used widely online in an attempt to provide indications of consumer opinions of products. Examples of sites which employ ratings scales are IMDb, Epinions.com, Yahoo! Movies, Amazon.com, BoardGameGeek and TV.com which use a rating scale from 0 to 100 in order to obtain "personalised film recommendations".
In almost all cases, online rating scales only allow one rating per user per product, though there are exceptions such as Ratings.net, which allows users to rate products in relation to several qualities. Most online rating facilities also provide few or no qualitative descriptions of the rating categories, although again there are exceptions such as Yahoo! Movies, which labels each of the categories between F and A+ and BoardGameGeek, which provides explicit descriptions of each category from 1 to 10. Often, only the top and bottom category is described, such as on IMDb's online rating facility.
Validity
Validity refers to how well a tool measures what it intends to measure. With each user rating a product only once, for example in a category from 1 to 10, there is no means for evaluating internal reliability using an index such as Cronbach's alpha. It is therefore impossible to evaluate the validity of the ratings as measures of viewer perceptions. Establishing validity would require establishing both reliability and accuracy (i.e. that the ratings represent what they are supposed to represent). The degree of validity of an instrument is determined through the application of logic/or statistical procedures. "A measurement procedure is valid to the degree that if measures what it proposes to measure."
Another fundamental issue is that online ratings usually involve convenience sampling much like television polls, i.e. they represent only the opinions of those inclined to submit ratings.
Validity is concerned with different aspects of the measurement process. Each of these types uses logic, statistical verification or both to determine the degree of validity and has special value under certain conditions. Types of validity include content validity, predictive validity, and construct validity.