Wechsler-Bellevue Intelligence Scale[edit]
The Wechsler-Bellevue tests were innovative in the 1930s because they:
gathered tasks created for nonclinical purposes for administration as a "clinical test battery",[5]
used the point scale concept instead of the age scale, and
included a non-verbal performance scale.[6][7]
The Point Scale Concept[edit]
In the Binet Scales (prior to the 1986 version) items were grouped according to age level. Each of these age levels were composed of a group of tasks that could be passed by two-thirds to three-quarters of the individuals in that level. This meant that items were not arranged according to content. Additionally, an individual taking a Binet test would only receive credit if a certain amount of the tasks were completed. This meant that falling short just one task required for the credit, resulted in no credit at all (for example, if passing three out of four tasks was required to receive credit, then passing two yielded no credit).[4]
The point scale concept significantly changed the way testing was done by assigning credits or points to each item. This had two large effects. First, this allowed items to be grouped according to content. Second, participants were able to receive a set amount of points or credits for each item passed.[8] The result was a test that could be made up of different content areas (or subtests) with both an overall score and a score for each content area. In turn, this allowed for an analysis to be made of an individual's ability in a variety of content areas (as opposed to one general score).[4]
The Non-Verbal Performance Scale[edit]
The non-verbal performance scale was also a critical difference from the Binet scale. Since the "early Binet scale had been persistently and consistently criticized for its emphasis on language and verbal skills," [4] Wechsler made an entire scale that allowed the measurement of nonverbal intelligence. This became known as a performance scale. Essentially, this scale required a subject to do something (such as "copying symbols or point to a missing detail"[4]) rather than just answer questions. This was an important development as it attempted to overcome biases that were caused by "language, culture, and education."[4] Further, this scale also provided an opportunity to observe a different type of behavior because something physical was required. Clinicians were able to observe how a participant reacted to the "longer interval of sustained effort, concentration, and attention" that the performance tasks required.[4]
While the Wechsler-Bellevue scale was the first to effectively use the performance scale (meaning that (1) there was a "possibility of directly comparing an individual's verbal and nonverbal intelligence",[4] and (2) that "the results of both scales were expressed in comparable units"[4]), the idea had been around for a while. The Binet scale did have performance tasks (although they were geared towards children) and there were entire tests that were considered supplements or alternatives (an example of such a performance test is the Leiter International Performance Scale)