I replied at https://phabricator.wikimedia.org/T105623. Lets keep the discussion
there.

Am 19.09.2015 um 21:14 schrieb Michael Peel:
>
>> On 19 Sep 2015, at 19:16, Daniel Kinzler <daniel.kinzler@wikimedia.de> wrote:
>>
>> Am 19.09.2015 um 10:27 schrieb Egon Willighagen:
>>>
>>>
>>> On Tue, Sep 15, 2015 at 10:12 PM, Michael Peel <email@mikepeel.net
>>> <mailto:email@mikepeel.net>> wrote:
>>>
>>>    It seems to assume a default uncertainty on values, though: I just added the
>>>    elevation above sea level to:
>>>    https://www.wikidata.org/wiki/Q1513315
>>>    just specifying the central value, and it assumes that this value is +- 0.1
>>>    km - which isn't a good assumption to make...
>>>
>>>
>>> Did you mean to write 2.80 km about sea level? Then the error would be 0.01 km
>>> .... I am guessing the uncertainty follows the scientific notation of the
>>> number... 2.8 has the numeric uncertainty of (about) +/- 0.1...
>>>
>>> That sounds like a reasonable approach to me...
>>
>> Yes, the uncertainty follows the scientific convention about significant digits.
>
> Taking that approach is a *really* bad idea. You can't just assume/make up uncertainties!
>
> As an example, say you have a length of 100m. Which significant digit do you assume is correct? Is this +- 100m, 10m or 1m? What if it's referring to the length of a 100m run, where the accuracy could be much higher than the significant digit given, e.g. 100m +- 1cm? Or what if it's the size of a crater on a distant planet, where it might be 100m+-50m? Or if the actual value is 100m +- 3m, but we say that it's +- 1m (which I see is the default in this case), which might be believable to readers but very misleading in reality?
>
>> We are currently thinking about adjusting this a bit, see
>> https://phabricator.wikimedia.org/T105623
>
> As thiemowmde says there:
> "The fact that the parser "guesses" a precision based on basically zero information always was and still is wrong. It must default to ±0. Everything else is misleading and a source of significant confusion and actual errors."
> ... although perhaps a better approach if possible might be to default to -1, or something else indicating the absence of data.
>
> Thanks,
> Mike
>
>
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--
Daniel Kinzler
Senior Software Developer

Wikimedia Deutschland
Gesellschaft zur Förderung Freien Wissens e.V.

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