This document describes a self-test to evaluate overconfidence by having participants provide low and high estimates for factual answers that they are 90% certain fall within that range. It lists 10 factual questions about topics like geography, history, and science. The goal is to have exactly one miss out of the 10 questions, indicating neither overconfidence with too narrow ranges nor underconfidence with too wide ranges.

1. SELF TEST OF OVERCONFIDENCE
For each item, provide a low and high guess such that you are 90%
sure the correct answer falls between the two.
Your challenge is to be neither too narrow (overconfident) nor too
wide (underconfident).
If you meet the challenge successfully you should have 10% misses
- that is, exactly one miss.
90% Confidence Range
LOW HIGH
01. Martin Luther King’s age at death 39
02. Length of the river Nile (miles) 4,187
03. Number of countries in OPEC 13
04. Number of books in the Old Testament 39
05. Diameter of the moon (miles) 2,160
06. Weight of an empty Boeing 747 (pounds) 390,000
07. Year Mozart was born 1756
08. Gestation period of Asian elephant (days) 645
09. Air distance from London to Tokyo (miles) 5,959
10. Deepest known point in the oceans (feet) 36,198
1 mile = 1.609 km 1 foot = 30.48 cm 1 pound = 0.454 kg

2. Incredible but True !
A group of 30 people - including entrepreneurs, business school
students and professionals - was asked to select the cube root of
64 from the numbers listed in column A below.
A B
4 8
8 12
16 3
32 7
In column B, write how many people you think selected that
number.