## Mean square ratio :

The mean squared ratio (MSR) is a statistical measure that is used to evaluate the precision of an estimated quantity. It is defined as the ratio of the mean squared error of an estimator to the mean squared error of a reference estimator, with the goal of determining whether the estimator under consideration is superior to the reference estimator.

To understand this concept, let’s consider a simple example. Suppose we are interested in estimating the weight of a certain object, and we have two different methods for doing so. The first method involves using a standard scale, while the second method involves using a more advanced and precise digital scale.

If we use the standard scale to weigh the object, we might get an estimate of 10 pounds. But if we use the digital scale, we might get an estimate of 9.8 pounds. In this case, the digital scale would be considered the superior estimator because its estimate is closer to the true weight of the object.

But how can we quantitatively compare the two estimators and determine which one is better? This is where the mean squared ratio comes in. The mean squared ratio is calculated by taking the ratio of the mean squared error (MSE) of the estimator under consideration to the mean squared error of a reference estimator.

The MSE is a measure of how far the estimated values are from the true values. It is calculated by taking the average of the squares of the differences between the estimated and true values. For example, if we have three estimates of the weight of the object (10 pounds, 9.8 pounds, and 9.9 pounds), the MSE would be calculated as follows:

MSE = ( (10 – 10)^2 + (9.8 – 10)^2 + (9.9 – 10)^2 ) / 3

= (0^2 + (0.2)^2 + (0.1)^2) / 3

= 0.03

In this case, the MSE is 0.03, which indicates that the estimated values are, on average, 0.03 pounds away from the true value.

Now, let’s consider the mean squared ratio. To calculate the mean squared ratio, we first need to define a reference estimator. In this example, let’s say that the reference estimator is the standard scale. We can then calculate the mean squared ratio as follows:

MSR = (MSE of digital scale) / (MSE of standard scale)

= (0.03) / (MSE of standard scale)

If the mean squared ratio is less than 1, it indicates that the estimator under consideration (in this case, the digital scale) is superior to the reference estimator (in this case, the standard scale). In other words, it has a lower MSE, which means that it produces estimates that are closer to the true values.

Another example of the mean squared ratio is in the context of hypothesis testing. In hypothesis testing, we are typically interested in comparing the performance of two different statistical models, with the goal of determining which model is better at making predictions.

Suppose we have two different models for predicting the stock market, and we want to determine which one is more accurate. We could use the mean squared ratio to compare the models by using one of the models as the reference estimator and calculating the mean squared ratio of the other model. If the mean squared ratio is less than 1, it would indicate that the model under consideration is superior to the reference model.

In conclusion, the mean squared ratio is a useful statistical measure that can be used to compare the performance of different estimators or statistical models. It is calculated by taking the ratio of the mean squared error of the estimator or model under consideration to the mean squared error of a reference estimator or model. If the mean squared ratio is less than 1, it indicates that the estimator or model under consideration is superior to the reference estimator or model. It is commonly used in a variety of applications, including weight estimation and hypothesis testing.