Consider five people, whom we have asked which brand of cola they last purchased. The first two said Coke. The following three said Pepsi. We can compute that 40% of people said Coke. This is an example of an unweighted calculation.
Now, consider the situation where we have also asked them how many they purchased, and the five respondents said 10, 5, 1, 2, and 2, respectively, as shown above. The total number of purchases is 20. If we sum up the Coke purchases, we get 15, which is 75%. This is an example of a weighted calculation, where:
- The number of purchases is the weight variable, and it contains in this example five weights (one for each person).
- If we were to replace the weight variable with five 1s instead, we would get the 40% obtained in the unweighted calculation. That is, unweighted calculations are just weighted calculations, where everybody has a weight of 1.