Cognitive Reflection Test Cognitive Reflection Probability and Statistical Intuition

Question 1

A disease affects 1 in 1,000 people. A test for it is 99% accurate. You test positive. What is the approximate probability you actually have the disease?

Accepted Answer

About 9%

Answer

With only 1 in 1,000 people having the disease, most positives are false positives, making the true probability roughly 9%.

Question 2

A fair coin is flipped 5 times and lands heads each time. What is the probability the next flip is heads?

Accepted Answer

Exactly 50%

Answer

Each coin flip is independent, so the probability of heads is always 50% regardless of prior results.

Question 3

In a group of 23 people, what is the approximate probability that two share a birthday?

Accepted Answer

About 50%

Answer

The Birthday Paradox shows that with just 23 people, there is approximately a 50% chance two share a birthday.

Question 4

If you flip a fair coin twice, what is the probability of getting at least one head?

Accepted Answer

75%

Answer

The only outcome without a head is TT (25%), so the probability of at least one head is 75%.

Question 5

A bag has 3 red and 7 blue marbles. You draw one without looking. What is the probability it is red?

Accepted Answer

30%

Answer

There are 3 red marbles out of 10 total, giving a probability of 3/10 = 30%.

Cognitive Reflection Test Practice Test

Cognitive Reflection Test Practice Test

Cognitive Reflection Test Cognitive Reflection Probability and Statistical Intuition