Weighting involves assigning weights to different cases in a data set when performing analysis. There are two common applications of weighting and multiple exotic applications/types.
The two common applications of weighting
Volumetric weighting is where each case in the data is assigned a value indicating, in some sense, its worth, and then this weight is used to perform weighted calculations (see Example of a Weighted Calculation).
- When calculating market share, sales of products can be volume-weighted by their price.
- When calculating market share from a survey, data can be volume-weighted based on how much people consumed.
Sampling weights have the goal of correcting for biases in how a sample has been collected. For example, if a population contains 49% men, but a sample for a survey contains only 26% men, the results can be weighted to correct for this under-representation.
A simple example of the creation and application of sampling weights is in Simple Worked Example of Creating and Applying a Sampling Weight. For more detail, see How to Weight a Survey.
Weighting a sample to deal with biases in data collection is also known as:
- Probability weighting
- Weighting survey data
- Sample balancing
- Calibration (which is technically a specific algorithm)
- Post-survey adjustment
- Raking (which is technically a specific algorithm)
- Non-response weighting
Exotic applications/types of weights
Although typically weighting refers to one of the above two types of weights, there are applications of the basic idea: