{ "id": 6781, "title": "How many people classified each galaxy ? [besides the typical 40-50 answer from web-page]", "url": "/competitions/galaxy-zoo-the-galaxy-challenge/discussion/6781", "author_name": "", "post_date": "2014-01-08T16:14:23.883Z", "votes": null, "comment_count": 5, "views": 1683, "content": "

It is stated that : 

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"Multiple individuals (typically 40-50) all classified the same galaxy"

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For example, galaxy with id 100045 has the following answer for the first question, this question is normalised to 1 for all objects.

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0.151045, 0.841492, 0.007462

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Option 3 was chosen in ~0.7% of the cases, if 50 people classified this object, and 1 person chose option three then this leads to 2% [0.02]

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It seems that for this object at least ~134 people classified it, with one person thinking it's a star.

Just out of curiosity what is the variance of the amount of people that have classified each galaxy ? is that data available ? (I doubt it will be of any use for the challenge)

\n

 

", "messages": [ { "id": "37136", "postDate": "01/08/2014 16:14:23", "content": "

It is stated that : 

\n

"Multiple individuals (typically 40-50) all classified the same galaxy"

\n

For example, galaxy with id 100045 has the following answer for the first question, this question is normalised to 1 for all objects.

\n

0.151045, 0.841492, 0.007462

\n

Option 3 was chosen in ~0.7% of the cases, if 50 people classified this object, and 1 person chose option three then this leads to 2% [0.02]

\n

It seems that for this object at least ~134 people classified it, with one person thinking it's a star.

Just out of curiosity what is the variance of the amount of people that have classified each galaxy ? is that data available ? (I doubt it will be of any use for the challenge)

\n

 

", "rawMarkdown": "", "votes": null }, { "id": "37137", "postDate": "01/08/2014 16:47:55", "content": "

Variance isn't that high; minimum of ~33, with a maximum of 70 or so. Majority have between 35 and 50 classifications.

", "rawMarkdown": "", "votes": null }, { "id": "37139", "postDate": "01/08/2014 17:01:48", "content": "

Hi Kyle,

\n

Thanks for your response. 
But how does one get an answer [0.151045, 0.841492, 0.007462] for question 1 with  70 people classifying ?  
The lowest classification you can get with only person voting for option 3  is 1/70 = 0.014
So implying that more people have classified galaxy 100045

Or am I missing something ? 

", "rawMarkdown": "", "votes": null }, { "id": "37140", "postDate": "01/08/2014 17:14:56", "content": "

The values in the data set aren't perfect vote fractions; they've been weighted & debiased in the processing, then renormalized so that they obey the constraints in the decision tree (see Section 3 in the Galaxy Zoo 2 paper).

\n

 

\n

So a given vote fraction might be less than 1/70, and most will exhibit fewer discrete values than you'd expect if it were just simple fractions.  

", "rawMarkdown": "", "votes": null }, { "id": "37141", "postDate": "01/08/2014 17:16:05", "content": "

Okay ! 

Thanks for the answer 

", "rawMarkdown": "", "votes": null }, { "id": "37183", "postDate": "01/09/2014 21:43:57", "content": "

For this challenge, the variance in the number of classifications per galaxy is likely to make little, if any, difference (as has already been said).

\n

 

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However, for the general situation - where the variance is greater, and the number of classifications per object not distributed even close to normally - the effect on some classifications will be considerable.

\n

 

\n

For example, in the first Galaxy Zoo and the 'bias study' (see Lintott+ 2008 and Land+ 2008) the number of classifications per galaxy varied from ~15 to well over 100. This produced an interesting effect in the  combined, unweighted classifications: all other things being equal, the number of SUPERCLEAN* objects falls as the number of classifications (per object) rises. I don't know the technical term for this, but it's an easily-understood effect: there's an upper limit on the fraction of votes for a particular class (per object), namely 100%; as the number of classifications rises, this vote fraction cannot increase, and will almost surely fall (someone will eventually click the wrong button by mistake, or misunderstand the question, or see something no one else before had seen, or ...). As far as I know, this effect is not discussed in any of the relevant Galaxy Zoo classification papers published so far.

\n

 

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* A SUPERCLEAN galaxy is one where the fraction of 'votes' for one class is 95+%

", "rawMarkdown": "", "votes": null } ], "comments": [ { "id": 37137, "author_name": "willettk", "author_url": "", "post_date": "01/08/2014 16:47:55", "content": "

Variance isn't that high; minimum of ~33, with a maximum of 70 or so. Majority have between 35 and 50 classifications.

", "votes": null, "replies": [] }, { "id": 37139, "author_name": "pl4770832", "author_url": "", "post_date": "01/08/2014 17:01:48", "content": "

Hi Kyle,

\n

Thanks for your response. 
But how does one get an answer [0.151045, 0.841492, 0.007462] for question 1 with  70 people classifying ?  
The lowest classification you can get with only person voting for option 3  is 1/70 = 0.014
So implying that more people have classified galaxy 100045

Or am I missing something ? 

", "votes": null, "replies": [] }, { "id": 37140, "author_name": "willettk", "author_url": "", "post_date": "01/08/2014 17:14:56", "content": "

The values in the data set aren't perfect vote fractions; they've been weighted & debiased in the processing, then renormalized so that they obey the constraints in the decision tree (see Section 3 in the Galaxy Zoo 2 paper).

\n

 

\n

So a given vote fraction might be less than 1/70, and most will exhibit fewer discrete values than you'd expect if it were just simple fractions.  

", "votes": null, "replies": [] }, { "id": 37141, "author_name": "pl4770832", "author_url": "", "post_date": "01/08/2014 17:16:05", "content": "

Okay ! 

Thanks for the answer 

", "votes": null, "replies": [] }, { "id": 37183, "author_name": "jeantate", "author_url": "", "post_date": "01/09/2014 21:43:57", "content": "

For this challenge, the variance in the number of classifications per galaxy is likely to make little, if any, difference (as has already been said).

\n

 

\n

However, for the general situation - where the variance is greater, and the number of classifications per object not distributed even close to normally - the effect on some classifications will be considerable.

\n

 

\n

For example, in the first Galaxy Zoo and the 'bias study' (see Lintott+ 2008 and Land+ 2008) the number of classifications per galaxy varied from ~15 to well over 100. This produced an interesting effect in the  combined, unweighted classifications: all other things being equal, the number of SUPERCLEAN* objects falls as the number of classifications (per object) rises. I don't know the technical term for this, but it's an easily-understood effect: there's an upper limit on the fraction of votes for a particular class (per object), namely 100%; as the number of classifications rises, this vote fraction cannot increase, and will almost surely fall (someone will eventually click the wrong button by mistake, or misunderstand the question, or see something no one else before had seen, or ...). As far as I know, this effect is not discussed in any of the relevant Galaxy Zoo classification papers published so far.

\n

 

\n

* A SUPERCLEAN galaxy is one where the fraction of 'votes' for one class is 95+%

", "votes": null, "replies": [] } ], "raw_markdown_by_id": { "37136": "", "37137": "", "37139": "", "37140": "", "37141": "", "37183": "" }, "source": "meta" }