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The PSLC Theoretical Hierarchy

Although the PSLC does not espouse a single theory of learning, it does encourage its researchers to maximize the overlap between each other’s theories. That is, to the maximum extent possible, a PSLC researcher’s explanation should use the same terminology and hypotheses as other PSLC researchers' explanations.

In order to display the integration achieved by this form of collaboration, the PSLC maintains a theoretical hierarchy. When a set of explanations share many terms and hypotheses, we make a node for each explanation, make a node for their common features, and link the nodes so that the common-feature node is the parent of each explanation node. In most cases a "node" is a single wiki page, but sometimes a node involves several wiki pages.

In order to more clearly display the integration, each node contains:

  1. An abstract that briefly describes the research encompassed by the node;
  2. A glossary that defines terms used elsewhere in this node but not defined in the nodes that are parents, grandparents, etc. of this node;
  3. The research question stated as concisely as possible, usually in a single sentence;
  4. A background and significance section that briefly summarizes prior work on the research question and why it is important to answer it;
  5. The dependent variables, which are observable and typically measure competence, motivation, interaction, meta-learning, or some other pedagogically desirable outcome;
  6. The independent variables, which typically include instructional environment, activity or method (the instructional "treatment" vs. "control"), and perhaps some student individual difference variables, such as gender or first language;
  7. The hypothesis, which is a concise statement of the relationship among the variables that answers the research question;
  8. The findings, which are the results of the study if it has been performed or the expected findings from the study if it has not -- explicitly indicate if the findings are preliminary;
  9. An explanation that describes the theoretical rationale for the hypothesis using the PSLC theoretical framework. It should be a paragraph or two and provide a causal chain that mentions mediating variables -- unobservable, hypothetical attributes of the students (e.g., knowledge components or path choices), how the treatment affects these, and how they, in turn, affect the dependent variables;
  10. The descendants, which lists links to descendant nodes of this one, if there are any;
  11. A further information section that points to documents using hyper links and/or references in APA format. Each indicates briefly the document's relationship to the node (e.g., whether the document is a paper reporting the node in full detail, a proposal describing the motivation and design of the study in more detail, the node for a similar PSLC research study, etc.).

Experience suggests that the glossaries carry much of the load in explaining the research, and that carefully defining and exemplifying terms often pays off later in reducing confusion and facilitating collaboration. Consequently, the glossaries are sometimes so long that they are spit off as separate wiki pages.

The root node of the hierarchy represents the research question addressed by the PSLC as a whole. It is necessarily abstract and is not the sort of question that can actually be tested by a single decisive experiment. This node is maintained by the PSLC co-directors.

The immediate descendants of the root node are three nodes representing the research questions address by each of the PSLC research clusters. That is, there are nodes for each of Coordinative Learning, Interactive Communication and Refinement and Fluency. These present somewhat more concrete research questions. They are specializations to the center’s overarching questions, and form a bridge to testable hypotheses posed by individual research projects. These 3 nodes are maintained by their respective clusters.

The leaves of the hierarchy (i.e., nodes with no descendants) represent individual research studies. A leaf node can also represent a group of studies or a whole project if the activities are sufficiently similar that it makes sense to summarize them with a single node. Each leaf node is maintained by its project’s leader.

Between the cluster nodes and the leaves, there may be some intervening nodes. For instance, if a group of Coordinative Learning studies all address a similar research question (e.g., how to use verbal and visual instruction together effectively), then a node may be created to summarize their shared aspects. Its parent is the Coordinative Learning cluster node, and its descendants are the relevant project nodes. These sub-cluster nodes are maintained by the cluster members.

At present, the hierarchy is a tree. That is, every node has at most one parent. If this parsimonious structure impedes theoretical development, we may relax the restriction and allow nodes to have multiple parents.

Click here for a draft, alternative framework based on independent dimensions of instruction

Note: The PSLC Theory Wiki is currently viewable to registered users only. If you would like to edit pages, register and email your username to PSLC Managing Director Michael Bett (mbett AT or wiki administrator Benjamin Billings (bkb AT