Good econometric analysis requires a good foundation of probability and statistics. The following free on-line learning course is suggested as a good probability and statistics refresher course: (The Coursera courses allow you to enroll (AUDIT) for free. The advertised fee is for a certificate, which isn’t necessary)
STATISTICS
Quick videos from YouTube: Great for reviewing your statistics before taking Econometrics
Expected Value: mean and variance
An Introduction to the Normal Disribution
An Introduction to Hypothesis Testing
Burkey Academy: Statistics and Econometrics
From Coursera: Probability and Statistics – to P or not to P and An Intuitive Introduction to Probability from Coursera
CALCULUS
Burkey Academy: Calculus review for Economics on YouTube.
Burkey Academy: Intermediate Microeconomics: Math Review you will find short video reviews on exponents, differentiation,, partial differentiation. Two of the most useful videos are Calculus Review for Economics: Basic Derivatives and Calculus Review for Economics: Partial Derivatives
MICROECONOMICS
Video: Burkey Academy: complete Introduction to Micro course videos and complete Intermediate Micro course videos
Textbook: OpenStax free book Principles of Microeconomics
Textbook: University of Minnesota Publishing Principles of Economics (Micro and Macro) complete on-line textbook
Video: Intromediate Microeconomics – a mix of intoroductory and intermediate/advanced Microeconomics
MACROECONOMICS
Textbook: OpenStax free book Principles of Macroeconomics