Notes

Friday, January 14, 2022

To read later: What Do We Know About Time Pressure in Software Development?

Introduction to Statistics

Week 2 of the Coursera Introduction to Statistics course

Selection bias

Learned the different types of bias in selecting a sample:

• Selection bias: Sample selected from a small, non-representative portion of the total population
• Non-response bias: People refuse or don’t take the time to respond if they are busy, e.g. parents during the evening
• Volontary response bias: People who feel strongly about a subject will respond more. e.g. restaurant reviews

Basic rules

Complement rule
P(not A) = 1 - P(A)

Equal outcome rule
If n is the number of possible outcomes and they are equally likely, then
P(A) = (number outcomes in A) / n

Addition rule
If A and B are mutually exclusive, then
P(A or B) = P(A) + P(B)

Multiplication rule
If A and B are independent, then
P(A and B) = P(A) P(B)

Conditional probability

Probability of B given A
P(B|A) = P(A and B) / P(A)

This gives the general multiplication rule:
P(A and B) = P(A) P(B|A)

Special case when events are independent: P(B) = P(B|A)

Bayes’ rule
P(B|A) = P(A|B) P(B) / P(A)

Expanded formula:
P(B|A) = P(A|B) P(B) / (P(A|B) P(B) + P(A|not B) P(not B))