1.
- a covariance matrix (also known as
dispersionmatrix or
variance–covariance matrix)
is a matrix whose element in the
i, j position is the covariance
between the i-th and j-th elements of a random vector. A random
vector is a random variable with multiple
dimensions.
- A measure used to represent how strongly two random variables
are related known as correlation.
Covariance is nothing but a measure of
correlation. On the contrary,
correlation refers to the scaled form of
covariance. Correlation is
dimensionless, i.e. it is a unit-free measure of the
relationship betweenvariables.
- A correlation matrix is a table showing
correlationcoefficients between sets of variables.
Each random variable (Xi) in the table is
correlated with each of the other values in the
table (Xj).
2.
Likelihood Ratio Tests are a powerful, very
general method of testing model when unknown parameters are
replaced by their maximum likelihood
estimates.
For construction refer to:-
https://ocw.mit.edu/courses/mathematics/18-443-statistics-for-applications-spring-2015/lecture-notes/MIT18_443S15_LEC10.pdf