Generalized Method of Moments (GMM) is a way to find out the unknown facts about certain things by using some data that we already have. Basically, it's a tool that helps us to figure out the answer to some questions that we don't know already.
Imagine you are playing a game where you have to guess how many candies are there in a jar. But you don't know the actual number of candies since you can't open the jar. So, you decide to use the weight of the jar and some other information to make an estimate. This process is called 'Generalized Method of Moments'.
In more technical terms, GMM is a statistical method that helps us to find the parameters of a model that best explain the observed data. It uses the principle of matching the theoretical moments of the data with the empirical moments calculated from the data.
To use GMM, we first define a model that we think can explain the data behavior. The model will include some unknown parameters that we want to estimate. Then, we collect some data that we think are related to the model, and we calculate some empirical moments from the data.
Next, we compare these empirical moments with the theoretical moments of the model. If they match, we have found the best estimate of the unknown parameters. If not, we adjust the parameters and repeat the process until we get a match.
In simple words, GMM is like a game where we have to match the toy blocks (theoretical moments) with the ones we have (empirical moments) to build a structure (the model). Once we get the right match, we have the answer we were looking for.
Overall, GMM is a powerful statistical tool that helps us to estimate unknown values, and it's used in many fields like economics, finance, physics, and engineering to name a few.