The document discusses key assumptions of linear regression models and the law of iterated expectations. It states that the law of iterated expectations means the expected value of a random variable can be calculated by considering the expected values of that variable conditioned on another random variable. As an example, it explains how to calculate the probability of rain tomorrow based on the probabilities of rain today and tomorrow given whether it rained today. It then briefly mentions linear regression model hypothesis testing and a session ID for an online response system. The summary covers the main topics and examples discussed in the document in 3 sentences.
11. Law of Iterated Expectations
The Law of Iterated Expectation states that the expected value of a random
variable is equal to the sum of the expected values of that random
variable conditioned on a second random variable. Intuitively speaking, the
law states that the expected outcome of an event can be calculated
using casework on the possible outcomes of an event it depends on; for
instance, if the probability of rain tomorrow depends on the probability of rain
today, and all of the following are known
The probability of rain today
The probability of rain tomorrow given that it rained today
The probability of rain tomorrow given that it did not rain today
the probability of rain tomorrow can be calculated by considering both cases (it rained
today/it did not rain today) in turn. To use specific numbers, suppose that
The probability of rain today is 70%
If it rains today, it will rain tomorrow with probability 30%
If it does not rain today, it will rain tomorrow with probability 90%
In this case, the probability of rain tomorrow is
0.70.3+0.30.9=0.21+0.27=0.48=48%