what is covariance vs variance 
covariance and variance are used to measure the distribution of points in a data set however variance is typically used in data sets with only one variable and indicates how closely those data points are clustered around the average covariance measures the direction of the relationship between two variables a positive covariance means that both variables tend to be high or low at the same time a negative covariance means that when one variable is high the other tends to be low 