Why doesn't the popular vote for past elections tally?

Question

Why does different sources show a different popular vote tally. This happens even in the most recent elections such as 2012, 2008, etc.

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I've complied the results from 3 sources:

1. Federal Elections Publication

   • a compilation of the official, certified federal election results obtained from each state’s election office and other official sources (quoted)

2. Dave Leip's Atlas

   • The site has been used a reference for U.S. election and political data by major media outlets. Leip's Atlas has been cited as a "preferred source for election results" by statistician and political pundit Nate Silver. (quoted from Wikipedia)

3. National Archives and Records Administration

   • These results are taken from each state's Certificate of Ascertainment. They will become available as the Certificates of Ascertainment are received and verified for completeness and accuracy. (quoted)

Both the FEC & archives.gov describe their results as official, yet they still differ. The difference ranges from hundreds to millions.

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+------+-----------+-------------------+-------------------+--------------+
| Year | Candidate | Federal Elections | Dave Leip's Atlas | archives.gov |
|      |           | Publication       |                   |              |
+------+-----------+-------------------+-------------------+--------------+
| 2012 | Obama:    | 65,915,795        | 65,918,507        | 65,446,032   |
|      | Romney:   | 60,933,504        | 60,934,407        | 60,589,084   |
| 2008 | Obama:    | 69,498,516        | 69,499,428        | 69,297,997   |
|      | McCain:   | 59,948,323        | 59,950,323        | 59,597,520   |
| 2004 | Bush:     | 62,040,610        | 62,039,572        | 60,693,281   |
|      | Kerry:    | 59,028,444        | 59,027,115        | 57,355,978   |
| 2000 | Bush:     | 50,456,002        | 50,462,412        | 50,996,582   |
|      | Gore:     | 50,999,897        | 51,009,810        | 50,456,062   |
| 1996 | Clinton:  | 47,402,357        | 45,590,703        | 47,400,125   |
|      | Dole:     | 39,198,755        | 37,816,307        | 39,198,755   |
| 1992 | Clinton:  | 44,909,889        | 44,909,806        | 44,908,254   |
|      | Bush:     | 39,104,545        | 39,104,550        | 39,102,343   |
+------+-----------+-------------------+-------------------+--------------+

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So,

• Why is this so?
• Which source can be considered the most "official"?

Answer 1

As blip's comment suggests, it looks like this is a result of each source accessing the data at different points in time.

For purposes of this post, I'm only going to look at two states in one election, but the examples can be applied more generally, too. I'm going to use Alabama (as the first state alphabetically) and California (as the state with the most votes cast) from 2012.

National Archives and Records Administration

This page lists the votes for each state.

Candidate vote totals are as listed on each state's Certificate of Ascertainment.

The Certificates are described here as:

After the general election, the Governor of each State and the Mayor of the District of Columbia prepare a Certificate of Ascertainment of the electors appointed (herein, the term "Governor" includes the Mayor of the District of Columbia). The Certificate of Ascertainment must list the names of the electors appointed and the number of votes received by each. It must also list the names of all other candidates for elector and the number of votes received by each. The Certificate must be signed by the Governor and carry the seal of the State. The format of the Certificate is not dictated by Federal law, but conforms to the law or custom of the submitting State.

The Governor must prepare seven original Certificates of Ascertainment. One original, along with two authenticated copies (or two additional originals) must be sent by registered mail to the Archivist of the United States, National Archives and Records Administration, Washington, DC 20408. The Certificates should be sent as soon as practicable after the election, but must be submitted to the Archivist no later than the day after the meetings of the electors... The other six originals must be delivered to the State's electors on or before [that date].

In other words, these numbers is pulled from the official document sent to the government when the electors vote, along with the documentation of how the electors voted. In other-other words, these are the numbers used for determining who "won" the election and whose electors get to vote.

• Alabama 2012 Certificate of Ascertainment
  • Electors pledged to Barack Obama and Joe Biden: 795,696 each
  • Electors pledged to Mitt Romney and Paul Ryan: 1,255,925 each
  • Electors pledged to Virgil H. Goode, Jr. and James N. Clymer: 2,981 each
  • Electors pledged to Gary Johnson and Jim Gray: 12,328 each
  • Electors pledged to Jill Stein and Cheri Honkala: 3,397 each
  • Total: 2,070,327 votes
  • Signed: December 4th, 2012
• California 2012 Certificate of Ascertainment
  • Electors pledged to Barack Obama and Joe Biden: 7,854,285 each
  • Electors pledged to Mitt Romney and Paul Ryan: 4,839,958 each
  • Electors pledged to Jill Stein and Cheri Honkala: 85,638 each
  • Electors pledged to Roseanne Barr and Cindy Sheehan: 53,824 each
  • Electors pledged to Thomas Hoening and Robert Ornelas: 38,372 each
  • Electors pledged to Ron Paul (write-in): 21,461 each
  • Electors pledged to Ross C. "Rocky" Anderson (write-in): 992
  • Electors pledged to Virgil Goode (write-in): 503
  • Electors pledged to Stewart Alexander (write-in): 82
  • Electors pledged to Jerry White (write-in): 79
  • Electors pledged to James Harris (write-in): 72
  • Electors pledged to Stephen Durham (write-in): 54
  • Electors pledged to Sheila "Samm" Tittl (write-in): 6
  • Total: 12,895,326 votes
  • Signed: December 15th, 2012

These are then added up across all states to generate the numbers displayed.

Dave Leip's Atlas

This page lists the votes for each state, and the sources are described here (change the year value in each link to get a different year).

As you can see from the second link, it's generally sourced from some official website in the early-November to early-December period. There's one citation for each state:

Alabama Alabama Office of the Secretary of State. State of Alabama Canvass of Results General Election November 6, 2012 - For President and Vice-President of the United States, Alabama Office of the Secretary of State (http://www.sos.state.al.us/downloads/election/2012/general/2012GeneralResults-AllStateAndFederalOfficesAndAmendments-WithoutWrite-inAppendix.pdf ) (accessed 05 Dec 2012)

California California Secretary of State, "President," Statement of Vote November 6, 2012, General Election (Sacramento, 2012)

In other words, these numbers are pulled from the State's official reporting, as of shortly after the election.

• Alabama: 2,074,338 total votes (December 5th, 2012)
• California: 13,055,815 total votes (Date unknown, 2012)

_{It's also worth noting that Nate Silver's comment was probably as much about the ease of working with the numbers as their accuracy. Dave Leip collectes all the raw data and makes it very accessible.}

Federal Elections Publication

These publications, describe themselves in the preface:

Data is based on official figures provided by State election officials, and includes results amended through July 2013. If the election results are modified in the future, the Commission will supply errata supplements as necessary. The assistance provided by the State election officials and their staff in the preparation of this publication is greatly appreciated.

In other words, these are the most recent official numbers reported, which are presumably final.

From their 2012 results:

• Alabama: 2,074,338 total votes
• California: 13,038,547 total votes

They do not indicate how many versions there were, or when earlier updates were made, but these numbers are as of July 2013, well after all the others.