Appendix 2: An Estimation Quiz

The back-of-the-envelope calculations in Column 7 all start with basic quantities. Those numbers can sometimes be found in a problem specification (such as a requirements document), but other times they must be estimated.

This little quiz is designed to help you evaluate your proficiency as a number guesser. For each question, fill in upper and lower bounds that, in your opinion, give you a ninety percent chance of including the true value; try not to make your ranges too narrow or too wide. I estimate that it should take you between five and ten minutes. Please make a good faith effort (and in consideration of the next reader, perhaps a photocopy of this page).

[_____,_____] January 1, 2000, population of the United States in millions.

[_____,_____] The year of Napoleon’s birth.

[_____,_____] Length of the Mississippi-Missouri river in miles.

[_____,_____] Maximum takeoff weight in pounds of a Boeing 747 airliner.

[_____,_____] Seconds for a radio signal to travel from the earth to the moon.

[_____,_____] Latitude of London.

[_____,_____] Minutes for a space shuttle to orbit the earth.

[_____,_____] Length in feet between the towers of the Golden Gate Bridge.

[_____,_____] Number of signers of the Declaration of Independence.

[_____,_____] Number of bones in the adult human body.

When you finish this quiz, please turn to the next page for answers and interpretation.

Please answer the questions before you turn the page.

If you have not yet filled in all the guesses yourself, please go back and do so. Here are the answers, from an almanac or similar source.

January 1, 2000, population of the United States is 272.5 million.

Napoleon was born in 1769.

The Mississippi-Missouri river is 3,710 miles long.

Maximum takeoff weight of a B747-400 airliner is 875,000 pounds.

A radio signal travels from the earth to the moon in 1.29 seconds.

Latitude of London is about 51.5 degrees.

A space shuttle orbits the earth in about 91 minutes.

4200 feet between the towers of the Golden Gate Bridge.

56 signers of the Declaration of Independence.

206 bones in the adult human body.

Please count how many of your ranges included the correct answer. Because you used a 90-percent confidence interval, you should have gotten about nine of the ten answers correct.

If you had all ten answers correct, then you may be an excellent estimator. Then again, your ranges may be way too big. You can probably guess which.

If you had six or fewer answers correct, then you are probably as embarrassed as I was when I first took a similar estimation quiz. A little practice couldn’t hurt your estimation skills.

If you had seven or eight answers correct, then you are a pretty good guesser. In the future, remember to broaden your 90-percent ranges just a bit.

If you had exactly nine answers correct, then you may be an excellent guesser. Or, you may have given infinite ranges for the first nine questions, and zero for the last question. If so, shame on you.