SOLO Taxonomy versus Bloom's Taxonomy

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The reasons why we prefer to use SOLO Taxonomy

The SOLO Taxonomy (Biggs & Collis, 1982), provides a measure of cognitive learning outcomes or understanding of thinking, that, in my experience, teachers have felt comfortable adopting. This hierarchical model is comprehensive, supported by objective criteria, and used across different subjects and on differing types of assignments (Hattie & Purdie, 1998). Teachers enjoy the way that SOLO represents student learning of quite diverse material in stages of ascending structural complexity, and that these stages display a similar sequence across tasks. Furthermore, surface or deep levels of understanding can be planned for and assessed by coding a student’s thinking performance against unistructural, multistructural, relational, or extended abstract categories, as shown in Table 1. Using visual symbols to represent levels of understanding in SOLO means that coding for complexity of thinking can be undertaken by both student and teacher, allowing “where should we go next?” decisions and thinking interventions to more accurately target student learning needs. Hook, P. 2006 A Thinking Curriculum NZCER p100

Notes from Professor John Hattie

Course 224: Assessment in the Classroom (The University of Auckland)

"Creating best tests using Bloom's taxonomy or the SOLO classification."


The taxonomy was published in 1956, has sold over a million copies, has been translated into several languages, and has been cited thousands of times.

The Bloom taxonomy has been extensively used in teacher education to suggest learning and teaching strategies, has formed the basis of many tests developed by teachers (at least while they were in teacher training), and has been used to evaluate many tests.

It is thus remarkable that the taxonomy has been subject to so little research or evaluation.

Most of the evaluations are philosophical treatises noting, among other criticisms, that there is no evidence for the invariance of these stages, or claiming that the taxonomy is not based on any known theory of learning or teaching.

  • The Bloom taxonomy presupposes that there is a necessary relationship between the questions asked and the responses to be elicited, whereas in the SOLO taxonomy both the questions and the answers can be at differing levels.
  • Whereas Bloom separates 'knowledge' from the intellectual abilities or process that operate on this 'knowledge' , the SOLO taxonomy is primarily based on the processes of understanding used by the students when answering the prompts. Knowledge, therefore, permeates across all levels of the SOLO taxonomy.
  • Hierarchy. Bloom has argued that his taxonomy is related not only to complexity but also to an order of difficulty such that problems requiring behaviour at one level should be answered more correctly before tackling problems requiring behaviour at a higher level. Although there may be measurement advantages to this increasing difficulty, this is not a necessary requirement of the SOLO method. It is possible for an item at the relational level, for example, to be constructed so that it is less difficult than an item at the unistructural level. For example, an item aiming to elicit relational responses might be 'How does the movement of the Earth relative to the sun define day and night'. This may be easier (depending on instruction, etc.) than a unistructural item that asks 'What does celestial rotation mean?'
  • Bloom’s taxonomy is not accompanied by criteria for judging the outcome of the activity (Ennis, 1985), whereas SOLO is explicitly useful for judging the outcomes. Take for example, a series of art questions suggested by Hamben (1984).

Knowledge. Who painted Guernica?

Comprehension. Describe the subject matter of Guernica.

Application. Relate the theme of Guernica to a current event.

Analysis. What compositional principles did Picasso use in Guernica?

Synthesis. Imagine yourself as one of the figures in Guernica and describe your life history?

Evaluation. What is your opinion of Picasso’s Guernica?

When using Bloom’s taxonomy, the supposition is that the question leads to the particular type of Bloom response. There is no necessary relationship, however, as a student may respond with a very deep response to the supposedly lower order question: 'Describe the subject matter of Guernica?' Similarly, a student may provide a very surface response to 'What is your opinion of Picasso’s Guernica'? When using the SOLO taxonomy, either the questions would be written in a different manner, or the test scorer would concentrate on classifying the responses only. An example of re-writing to maximise the correspondence between the question asked and the answer expected is:

Unistructural. Who painted Guernica?

Multistructural. Outline at least two compositional principles that Picasso used in Guernica.

Relational. Relate the theme of Guernica to a current event.

Extended Abstract. What do you consider Picasso was saying via his painting of Guernica?

Advantages of the SOLO model for evaluation of student learning

  • There are several advantages of the SOLO model over the Bloom taxonomy in the evaluation of student learning.
  • These advantages concern not only item construction and scoring, but incorporate features of the process of evaluation that pay attention to how students learn, and how teachers devise instructional procedures to help students use progressively more complex cognitive processes.
  • Unlike the Bloom taxonomy, which tends to be used more by teachers than by students, the SOLO can be taught to students such that they can learn to write progressively more difficult answers or prompts.
  • There is a closer parallel to how teachers teach and how students learn.
  • Both teachers and students often progress from more surface to deeper constructs and this is mirrored in the four levels of the SOLO taxonomy.
  • There is no necessary progression in the manner of teaching or learning in the Bloom taxonomy.
  • The levels can be interpreted relative to the proficiency of the students. Six year old students can be taught to derive general principles and suggest hypotheses, though obviously to a different level of abstraction and detail than their older peers. Using the SOLO method, it is relatively easy to construct items to assess such abstractions.
  • The SOLO taxonomy not only suggests an item writing methodology, but the same taxonomy can be used to score the items. The marker assesses each response to establish either the number of ideas (one = unistructural; _ two = multistructural), or the degree of interrelatedness (directly related or abstracted to more general principles). This can lead to more dependability of scoring.
  • Unlike the experience of some with the Bloom taxonomy it is relatively easy to identify and categorise the SOLO levels.
  • Similarly, teachers could be encouraged to use the 'plus one' principle when choosing appropriate learning material for students. That is, the teacher can aim to move the student one level higher in the taxonomy by appropriate choice of learning material and instructional sequencing.

Also read

Questioning Bloom's and Gagne's significance

- Verb alignment

Problems with Bloom's Taxonomy

- Invalid, unreliable, impractical

SOLO References:

Cognitive processes in asTTle: The SOLO taxonomy. asTTle Technical Report #43, University of Auckland/Ministry of Education.


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