Dictionary of Evidence-based Medicine.pdf
Dictionary of Evidence-based Medicine.pdf
Dictionary of Evidence-based Medicine.pdf
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<strong>Dictionary</strong> <strong>of</strong> <strong>Evidence</strong>-<strong>based</strong> <strong>Medicine</strong> 35<br />
The contingency table shown is a 3 row x 2 column table and is usually<br />
referred to simply as a 3 x 2 table; 2x2 tables are particularly commonly<br />
encountered. Multidimensional contingency tables are widely used in advanced<br />
categorical data analyses but require advanced graphical multivariate<br />
methods for representation on paper.<br />
Contingent valuation<br />
Estimates <strong>of</strong> willingness to pay for goods for which there is no market can<br />
be obtained using survey methods. Individuals are asked how much they<br />
would be willing to pay to avoid or overcome a certain state (e.g. avoidance<br />
<strong>of</strong> a particular morbidity). Using such an approach, sometimes referred<br />
to as 'contingent valuation' or expressed preference, the questions<br />
can be either open-ended or binary (Figure 5). In the former, the patient is<br />
asked the maximum amount he or she would be prepared to pay for the<br />
current treatment in a face-to-face or telephone interview or questionnaire.<br />
In order to improve response rate, response aids such as a bidding game<br />
are used. The patient is shown a value which is either rejected or accepted.<br />
The value is then altered until the maximum payment which is acceptable<br />
to the patient is identified. Alternatively, the patient may be shown a range<br />
<strong>of</strong> payment values from which a choice is made. The open-ended approach<br />
Figure 5 Contingent valuation: The calculation <strong>of</strong> willingness to pay using the binary<br />
contingent valuation method