<p>One theory that may explain this is is Kahneman and Tversky's <a href="http://en.wikipedia.org/wiki/Anchoring" rel="nofollow">anchoring heuristic</a>.</p>

<p>If you ask how much fuel the space shuttle needs, most people don't have the proper background knowledge to answer this accurately. Instead, they'll rely on a piece of information they do know--e.g., how much fuel a car needs--and adjust from there. Responses will be biased towards the anchor. Since a car requires very little fuel in comparison (~12 gallons), people will tend to underestimate the true response (~<a href="http://www.nasa.gov/centers/kennedy/about/information/shuttle_faq.html" rel="nofollow">500,000 gallons</a>).</p>

<p>If you first told them: The cruise ship The Norwegian Dream holds roughly 350,000 gallons of fuel, and <em>then</em> asked how much fuel weight the space shuttle needs, their answers will likely be closer to the truth. (Though there is the confounding variable of size-- larger vessels need more fuel, but even small vessels will need a lot of fuel to launch into space).</p>

<p>When it comes to horses, people have more accurate anchors-- such as a human, or an elephant-- and will tend to make more accurate judgments.</p>

<p>Although there are certainly more cues that people use to make size judgments, a complete theory must take into account one's background knowledge. Thus, even the anchoring heuristic   is limited in that we must know what people are likely to use as an anchor for any given question.</p>

CC BY-SA 3.0
2012-02-16T09:06:17.163Z
Thanks, I can see how the anchoring heuristic would be relevant, and you explain very clearly why this might be. Might other heuristics also be relevant? In relation to the [Availability Heuristic](http://en.wikipedia.org/wiki/Availability_heuristic) we might ask for an estimate of the weight of the average American and find the answer is biased upward by the many cultural depictions of overweight Americans which readily come to mind.
user1205901 - Слава Україні
CC BY-SA 3.0
2012-02-16T14:29:10.097Z
Yes, I think you are right in that example. That's part of the problem with the heuristics approach: there have been dozens of reported heuristics, but often it is not clear a priori which heuristic we might use for any given problem (though see Payne, Bettman & Johnson, 1988; Shah & Oppenheimer, 2008; etc)
Jeff
CC BY-SA 3.0
2012-02-15T22:50:03.047Z
2012-06-06T19:42:26.377Z
2012-06-06T19:42:26.377Z
Jeff
<p><strong>What psychological theories predict whether individuals will underestimate or overestimate when responding to particular kinds of general knowledge quantity questions?</strong></p>

<p>For instance, I have seen an unpublished study in which people were asked to guess the weight of the fuel in a certain space shuttle, and almost everyone wildly underestimated the weight. Then in another question they were asked to guess the weight of the horse which won the last Kentucky Derby and the responses were distributed fairly evenly around the truth. Why is this?</p>

<p>I think that the heuristics and biases literature must be relevant here, but I haven't found any citations that allow me to make predictions which are sufficiently specific.</p>

<cognitive-psychology>
What causes systematic under- or over-estimation of general knowledge quantities?
user1205901 - Слава Україні
# What causes systematic under- or over-estimation of general knowledge quantities?

(Asked by: username_0 on 2012-02-15)

**What psychological theories predict whether individuals will underestimate or overestimate when responding to particular kinds of general knowledge quantity questions?**

For instance, I have seen an unpublished study in which people were asked to guess the weight of the fuel in a certain space shuttle, and almost everyone wildly underestimated the weight. Then in another question they were asked to guess the weight of the horse which won the last Kentucky Derby and the responses were distributed fairly evenly around the truth. Why is this?

I think that the heuristics and biases literature must be relevant here, but I haven't found any citations that allow me to make predictions which are sufficiently specific.

**Tags:** cognitive-psychology


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## 1 answers

### Answer by username_1 on 2012-02-15. Score: 10 | Accepted answer

One theory that may explain this is is Kahneman and Tversky's [anchoring heuristic](http://en.wikipedia.org/wiki/Anchoring).

If you ask how much fuel the space shuttle needs, most people don't have the proper background knowledge to answer this accurately. Instead, they'll rely on a piece of information they do know--e.g., how much fuel a car needs--and adjust from there. Responses will be biased towards the anchor. Since a car requires very little fuel in comparison (~12 gallons), people will tend to underestimate the true response (~[500,000 gallons](http://www.nasa.gov/centers/kennedy/about/information/shuttle_faq.html)).

If you first told them: The cruise ship The Norwegian Dream holds roughly 350,000 gallons of fuel, and *then* asked how much fuel weight the space shuttle needs, their answers will likely be closer to the truth. (Though there is the confounding variable of size-- larger vessels need more fuel, but even small vessels will need a lot of fuel to launch into space).

When it comes to horses, people have more accurate anchors-- such as a human, or an elephant-- and will tend to make more accurate judgments.

Although there are certainly more cues that people use to make size judgments, a complete theory must take into account one's background knowledge. Thus, even the anchoring heuristic is limited in that we must know what people are likely to use as an anchor for any given question.

> **Comments:**
> **username_0**: Thanks, I can see how the anchoring heuristic would be relevant, and you explain very clearly why this might be. Might other heuristics also be relevant? In relation to the [Availability Heuristic](http://en.wikipedia.org/wiki/Availability_heuristic) we might ask for an estimate of the weight of the average American and find the answer is biased upward by the many cultural depictions of overweight Americans which readily come to mind.  
> **username_1**: Yes, I think you are right in that example. That's part of the problem with the heuristics approach: there have been dozens of reported heuristics, but often it is not clear a priori which heuristic we might use for any given problem (though see Payne, Bettman & Johnson, 1988; Shah & Oppenheimer, 2008; etc)  

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