How to estimate IQ for public figures? Background: I read a question on Quora that asked how intelligent is Barack Obama. A wide range of arguments were presented. The tone of the answers was not neutral because of the political context of the question. Furthermore, over the while I've read estimates of intelligence of various famous people from history (e.g., scientists, presidents, etc.). Issues were also raised about how intelligence is defined (e.g., cognitive, social, emotional or physical; achievement versus latent ability, etc.)
Despite these issues, I find the topic interesting. 

Questions:


If you cannot administer a standardised intelligence test to someone, to what extent can you obtain a good estimate of their IQ from the kinds of information available about public figures?
What is considered scientific best-practice in this regard?
How accurate is best practice? Do any studies provide validity estimates (e.g., correlating estimates with actual IQ test scores)? 


In relation to public figures, a wide range of information is often available: e.g., demographics, educational attainments, career achievement, writing samples, personal achievements, samples of public speaking, and so on. Sometimes, information such as school and university grades will be available. Of course, a lot of this information will be non-standardised. I wonder what would be a good way to collect and synthesise this information to generate a prediction.
Entry into the literature

As a starting point, Simonton (2009) provides an excellent introduction to the field of historiometric assessment of intelligence. To quote the abstract:


  Running parallel to mainstream research on the psychometric assessment
  of intelligence is another tradition of research on the historiometric
  assessment of intelligence and closely affiliated variables.
  Historiometric assessment is based on four data sources: (a)
  personality sketches (e.g., Intellectual Brilliance), (b) developmental histories (e.g., IQ), (c) content analyses (e.g., integrative
  complexity), and (d) expert surveys (e.g., Openness to Experience).
  The first two represent major lines of intelligence research that
  involved key figures in the development of corresponding psychometric
  methods (e.g., Galton, Terman, and Thorndike), whereas the last two
  constitute independent research paradigms that later intersected with
  the first two. The literature on U.S. presidents then provides an
  integrated illustration of the four historiometric approaches and how
  they converge on the same broad conclusions. Significantly,
  historiometric investigations on the relation between broadly defined
  intelligence and adulthood achievement obtain about the same effect
  size as that found in psychometric research (i.e., $r$ or $\beta$ .25 $\pm$
  .10). Because historiometric and psychometric studies have rather
  distinctive methodological advantages and disadvantages, this
  consistent outcome provides corrobora- tive support for both sets of
  empirical findings.


The review summarises various studies aiming to assess intelligence of royalty, U.S. politicians, and eminent figures.

Critical thoughts

For current and recent public figures substantial additional information would be available. In particular, many powerful predictors of IQ would often be available including university grades, scores on standardised assessments, SAT scores and so on. Furthermore, the existing literature on IQ correlates is huge and provides substantial information that could inform predictive models of IQ prediction. In contrast where such models are applied to the past, the predictive power of such models may be wrong.

I'd also be extremely wary of estimates of intelligence that yield estimates like 200 (i.e., around 7+ standard deviations above the mean). E.g., 


  After comparing the chronological age in which .. achievements
  appeared with the mental age that they represented, Terman decided
  that Galton’s IQ must have been close to 200. (Simonton, 2009, p. 319)


The expertise literature has highlighted the importance of not confusing eminence with IQ. Eminence is substantially influenced by years of practice, training, focus, opportunity, and luck. IQ is useful, but the correlation between IQ and eminence is insufficient to yield the kind of certainty in prediction to result in IQ predictions above something like 3 or perhaps 4 standard deviations above the mean (i.e., 145 to 160).

References


Simonton, D.K. (2009) The “other IQ”: Historiometric assessments of intelligence and related constructs. Review of General Psychology, 13, 315.