Are you good at estimating?

We all estimate. Whenever we say, “I’ll be home in about 30 minutes” or “I need about 50 inches of tape”, we are estimating. Some of us even estimate as part of our jobs. Project managers, sales reps, executives, coders… whether we estimate lines of code, weeks of effort, new customers, revenue and profit, we make educated guesses based on our experience, observations and other sources.

But how good are we at estimating?

Here is a little exercise. On a sheet of paper, write down 1 through 10 on the left side of the page. Next to each number, draw two blanks, so that you can provide two answers for each number. Like this:

1. _________ _________
2. _________ _________
3. _________ _________
4. _________ _________

and so on to “10”.

Your job is to provide a “90% certainty” estimate for the questions below. You don’t have to get the answer correct, just provide a range of numbers–write your “low estimate” on the first blank and your “high estimate” on the second blank on each line.

  1. What was the production cost of “Gone with the Wind”?
  2. How old was Alexander the Great when he died?
  3. Wikipedia lists Burj Khalifa in Dubai as the tallest building. How tall is it in feet (or meters)?
  4. If you walk at the average speed of 3 miles/hour, how long in months would it take to walk the distance of Earth’s equator?
  5. How many times can Earth fit inside Jupiter?
  6. How many people signed the US Declaration of Independence?
  7. How many countries are there in South America?
  8. In what year did the world’s population surpass 2 billion people?
  9. How many pairs of legs does a common house centipede (Scutigera coleoptrato) have?
  10. What is the “as the crow flies” distance (on miles or km) between Beijing, China and Amsterdam, Netherlands?

For answers and the second part of this post, see comments.  But don’t scroll down or click on link before you take the quiz!

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Comments

  • hcpark  On April 30, 2010 at 7:57 AM

    Answers:

    1. What was the production cost of “Gone with the Wind”? | $3.9 Million USD
    http://www.imdb.com/title/tt0031381/trivia

    2. How old was Alexander the Great when he died? | 32

    3. Wikipedia lists Burj Khalifa in Dubai as the tallest building. How tall is it in feet (or meters)? | 828 m or 2,717 ft

    4. If you walk at the average speed of 3 miles/hour, how long in months would it take to walk the distance of Earth’s equator? | 11 to 12 months

    5. How many times can Earth fit inside Jupiter? | 1,320

    6. How many people signed the US Declaration of Independence? | 56

    7. How many countries are there in South America? | 12

    8. In what year did the world’s population surpass 2 billion people? | 1927, http://en.wikipedia.org/wiki/World_population

    9. How many pairs of legs does a common house centipede (Scutigera coleoptrato) have? | 15

    http://www.enotes.com/science-fact-finder/animal-world/how-many-pairs-legs-does-centipede-have

    10. What is the “as the crow flies” distance (on miles or km) between Beijing, China and Amsterdam, Netherlands? | 7,830 km or 4.866 miles
    http://www.geobytes.com/CityDistanceTool.htm?d&pt_1=cnbjbeij&pt_2=nlnhamst

    How did you do? Since you were asked to provide a “90% certainty” estimate, you should have successfully gotten the range to be on both sides of the correct answer in 9 out of 10 questions.

    I got the idea for the quiz from The Black Swan, by Nassim Nicholas Taleb, and Super Crunchers, by Ian Ayers. Ayers provides his own set of 10 questions in his book. Taleb describes our inability to estimate (especially in areas where we are supposed to be experts!) to illustrate “epistemic arrogance”. We tend to overestimate how much we know and underestimate uncertainty.

    Which ONE question did you miss? OK, just so that you don’t feel so bad, Ayers and Taleb indicate that people generally do poorly on tests that test for “how well we think we know something”. Most people will miss between four to seven questions.

    Were you surprised that you missed questions where you actually had some knowledge or took the time to think through a correct answer? For some reason, we tend to be overconfident, especially in areas where we have some knowledge.

    The next time you are asked to “spec out the size of a database”, “determine number of weeks for a project”, or “guess at a revenue number”, maybe you should remember this test. Better yet, BEFORE you ask someone else to estimate something for you, have them take this test.

  • Nils Jonsson  On April 30, 2010 at 9:02 AM

    A humbling test of estimation abilities.

    1. $250,000-$3 million [WRONG]
    2. 23-85 years
    3. 1800-2400 feet [WRONG]
    4. 18-36 months [WRONG]
    5. 200-800 times [WRONG]
    6. 16-85 people
    7. 3-8 countries [WRONG]
    8. 1890-1975
    9. 40-160 legs [WRONG]
    10. 5000-10,000 miles [WRONG]

    An interesting feature of epistemic arrogance is that the more we are *supposed* to know about something, the less comfortable we are supplying a broad-ranged estimate.

    > “How long will this take?”
    >
    > “Um, two weeks to … 36 months?”
    >
    > “WHAT!? I thought you knew what you were doing here!”

    The truth is, though, that people with the most valuable expertise know what it is they don’t know, and they aren’t afraid to admit it specifically. What you don’t know *can* hurt you.

    The more experience I gain, however, the less I worry about precise estimates. Adapting to changing circumstances and new knowledge is more important that hitting a number somebody pulled out of the air. When the actuals begin to exceed the estimate, it’s a good time to reevaluate whether to continue or change course.

    Looking forward to more thought-provoking and informative posts, Howard!

  • Todd Cimino  On May 10, 2010 at 5:51 AM

    Tough quiz. Although I expected to have my ranges well protected, I missed 3 of the questions (two of them having to do with the circumference of the earth). When it comes to estimating, I suppose I must agree that we are all pretty bad at it.

    Although I’m not under any illusions that my estimating abilities are superb, at least I can bask in the glory of knowing that my estimating abilities are better than my wife’s. My wife’s estiamtes are typically off by orders of magnitude, which makes it difficult to properly plan simple things like:
    * elapsed time it takes to get to the grocery store
    * number of 2nd graders that can fit in a school bus
    * number of days of inventory of toilet paper we have in the house (we can wrap every tree in the entire neighborhood with what we have in the house)

  • Edwin  On June 22, 2010 at 9:56 AM

    I did not do range
    1. $100K
    2. 35
    3. 2500 ft
    4. 35
    5. 1500
    6. 60
    7. 15
    8. 1930
    9. 20
    10. 6000 miles

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