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In phylogenetics, a single-access key (also called dichotomous key, sequential key, analytical key, [1] or pathway key) is an identification key where the sequence and structure of identification steps is fixed by the author of the key. At each point in the decision process, multiple alternatives are offered, each leading to a result or a ...
A single-access key (also called a sequential key or an analytical key), has a fixed structure and sequence. The user must begin at the first step of the key and proceed until the end. A single-access key has steps that consist of two mutually exclusive statements (leads) is called a dichotomous key. Most single-access keys are dichotomous. [3]
In biology or medicine, a multi-access key is an identification key which overcomes the problem of the more traditional single-access keys (dichotomous or polytomous identification keys) of requiring a fixed sequence of identification steps.
Four types of response scales for closed-ended questions are distinguished: Dichotomous, where the respondent has two options. The dichotomous question is generally a "yes/no" close-ended question. This question is usually used in case of the need for necessary validation. It is the most natural form of a questionnaire.
In a diagnostic key, the branching structure of the key should not be mistaken for a phylogenetic or cladistic branching pattern. All single-access keys form a decision tree (or graph if reticulation exists), and thus all such keys have a branching structure. "Branching key" may therefore occasionally be used as a synonym for single-access key.
The typical multiple choice item is dichotomous; even though there may be four or five options, it is still scored only as correct/incorrect (right/wrong). Another class of models apply to polytomous outcomes, where each response has a different score value.
It is a special case of Cronbach's α, computed for dichotomous scores. [2] [3] It is often claimed that a high KR-20 coefficient (e.g., > 0.90) indicates a homogeneous test. However, like Cronbach's α, homogeneity (that is, unidimensionality) is actually an assumption, not a conclusion, of reliability coefficients.
Polychotomous key refers to the number of alternatives which a decision point may have in a non-temporal hierarchy of independent variables. The number of alternatives are equivalent to the root or nth root of a mathematical or logical variable.