< Previous | Next | Contents >

## What is Pairwise Comparison?

Now let me explain what paired comparison is. It is always easier to explain by an example. Suppose we have two fruits A pple and B anana. I would like to ask you, which fruit you like better than the other and how much you like it in comparison with the other. Let us make a relative scale to measure how much you like the fruit on the left (Apple) compared to the fruit on the right (Banana).

If you like the apple better than banana, you thick a mark between number 1 and 9 on left side, while if you favor banana more than apple, then you mark on the right side.

For instance I strongly favor banana to apple then I give mark like this

Now suppose you have three choices of fruits. Then the pair wise comparison goes as the following

You may observe that the number of comparisons is a combination of the number of things to be compared. Since we have 3 objects (Apple, Banana and Cheery), we have 3 comparisons. Table below shows the number of comparisons.

Table 7: Number of comparisons

 Number of things 1 2 3 4 5 6 7 number of comparisons 0 1 3 6 10 15 21

The scaling is not necessary 1 to 9 but for qualitative data such as preference, ranking and subjective opinions, it is suggested to use scale 1 to 9.

In the next section, you will learn how to analyze these paired comparisons