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From |
Richard Williams <richardwilliams.ndu@gmail.com> |

To |
statalist@hsphsun2.harvard.edu, statalist@hsphsun2.harvard.edu |

Subject |
Re: st: rounding the minimum of a negative number |

Date |
Thu, 10 Jan 2013 10:36:09 -0500 |

At 09:53 AM 1/10/2013, Maarten Buis wrote:

On Thu, Jan 10, 2013 at 3:19 PM, annoporci wrote: > Yes. I guess another way of expressing my puzzlement is that Stata does > not display, by default, to a greater number of decimal places. Stata is a program for statistical analysis. In any real statistical analysis involving real data, any number beyond the first (maybe, if you are lucky the second) is in essence random noice. So from that perspective Stata is reporting way too many digits.

This is not to say that precision is not a problem. During computations numerical precision is a major issue. However, my impression, based on the couple of contacts I have had with the people from StataCorp (mainly at Stata Users' Group meetings and just reading what they have written), is that StataCorp tends to take this extremely seriously. > I don't know anything about this, but in Python, for instance, according > to the documentation: "On a typical machine running Python, there are 53 > bits of precision available for a Python float." And, to quote more: > > If Python were to print the true decimal value of the binary approximation > stored for 0.1, it would have to display: > > 0.1000000000000000055511151231257827021181583404541015625 > > So that's still quite a few zeros after the first 1. Compare that with Stata: . di %30.25f 0.1 0.1000000000000000100000000 Does not look too different to me. > Would I get a more accurate approximation of "-1.981" with Stata if I > input "-1.981000000001" than if I input "-1.981" ? in the sense that it > would "force" Stata to store the zeros after 981? (or am I > misunderstanding the whole issue?) If you want to store a number equivalent to -1.981 exactly than you need think in terms of integers, as computers can store integers up to a given size(*) exactly. In this case you would store the number 1981. Hope this helps, Maarten (*) To see the limits see the the reference Nick gave you: <http://blog.stata.com/2012/04/02/the-penultimate-guide-to-precision/> and the references therein. -- --------------------------------- Maarten L. Buis WZB Reichpietschufer 50 10785 Berlin Germany http://www.maartenbuis.nl --------------------------------- * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

------------------------------------------- Richard Williams, Notre Dame Dept of Sociology OFFICE: (574)631-6668, (574)631-6463 HOME: (574)289-5227 EMAIL: Richard.A.Williams.5@ND.Edu WWW: http://www.nd.edu/~rwilliam * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: rounding the minimum of a negative number***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**st: rounding the minimum of a negative number***From:*annoporci <annoporci@gmail.com>

**Re: st: rounding the minimum of a negative number***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: rounding the minimum of a negative number***From:*annoporci <annoporci@gmail.com>

**Re: st: rounding the minimum of a negative number***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: rounding the minimum of a negative number***From:*annoporci <annoporci@gmail.com>

**Re: st: rounding the minimum of a negative number***From:*Maarten Buis <maartenlbuis@gmail.com>

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