Specifying Ratings

To specify the ratings for a criterion, first create a rating ruler in the criterion you are interested in, and then double click on the rating ruler icon  . This will open the rating ruler in a tab in the content pane of the Tetra window. Once this ruler is open, you may select a Reference Rating ruler, add alternatives, and rate their performance on this criterion. Note that ratings are specified on a scale with no lower or upper bounds relative to the Reference Alternatives on a Reference Rating ruler or the default Reference Alternatives.

Adding alternatives to the rating ruler

When a rating ruler is first opened it is empty. You need to add the alternatives to the ruler that you want to specify ratings for. To add alternatives you can:

• Right click on blank space in the rating ruler, choose Add Alternative, and then select either Add All, or choose the alternative you want to add, or
• Choose Add Alternative from the Ruler menu, and then select either Add All, or choose the alternative you want to add.

Once you have added alternatives to the rating ruler it will look similar to the following:

Click on the image for a larger version. To return to this page, press the back button.

Rating Alternatives

Once you have the alternatives on the rating ruler, you can specify values for the ratings of each alternative in two ways:

• Numerically — enter values into the table below the ruler.
• Graphically — drag the alternatives along the ruler to specify the ratings.

Tetra lets you specify relative ratings between alternatives. To do this, left and right alternatives are used. The default reference alternative Z/0 (value 0) is used for the left alternative, and the default reference alternative H/100 (value 100) is used for the right alternative. To choose a different left or right reference alternative, right click on the alternative or reference alternative you wish to use and choose Set Left or Set Right, respectively, or select the alternative or reference alternative you wish to use and choose Set Left or Set Right, respectively, from the Ruler menu. In the figure, the Townhouse has been set to be the left alternative and the 2-storey has been set to be the right reference alternative.

In the rating ruler, the red bar indicates the difference between the left and right alternatives. When an alternative is selected, the blue bar indicates the difference between this alternative and the left alternative, and the green bar indicates the difference to the right one. Furthermore, the value in the box on the line above the selected alternative shows the relative rating of the selected alternative relative to the left and right alternatives (the ratio of the blue bar to the red one). In the figure we see that the Condominium is rated as being halfway between the Townhouse and the 2-storey with respect to this criterion. You can set the left and right alternatives back to the default reference alternative Z/0 or the default reference alternative H/100 by right clicking anywhere in the rating ruler and choosing Clear Left or Clear Right, respectively.

If you "hover" the mouse over an alternative or reference alternative for a moment, the numerical value for the alternative will be displayed. Note that when the left alternative is set to Z/0 and the right alternative is set to H/100, this numerical value is the same as the relative value displayed for a selected alternative.

Reference Alternatives and Reference Ratings

The reference alternatives displayed on the top portion of the ruler are those belonging to the reference rating selected in the 'Reference Rating' list box below the ruler; this list contains all of the reference ratings that exist in the model. Please see the Reference Ratings section for details on how to create and specify reference ratings.

To deselect a reference rating and display only the default reference alternatives Z/0 and H/100, click inside the reference rating list box below the last item.