The OP cited a report by the ADB.
''the majority of the Asian middle class still falls in the $2–$4 range''
http://www.adb.org/sites/default/files/publication/27726/ki2010-special-chapter.pdf
It recognizes $2 as the threshold to be middle class.
Their graphs use this criteria:
Lower Middle ($2–$4)
Mid Middle ($4–$10)
Upper Middle ($10–$20)
Affluent (>$20)
As always, the devil is in the details:
A. Defining the Middle Class
Unlike poverty, which can be defined in absolute terms
based on caloric requirements, there is no standard
definition of the middle class. Different researchers use
different criteria—some absolute, others relative. This
report uses an absolute approach defining the middle class
as those with consumption expenditures of $2–$20 per
person per day in 2005 PPP $.6
Easterly (2001) and others have defined the middle
class as those in the second, third, and fourth quintile of
the distribution of per capita consumption expenditure,
while Birdsall, Graham and Pettinato (2000) have defined
it to include individuals earning between 75% and 125%
of a society’s median per capita income.
Other researchers have also defined the middle
class in absolute terms. Banerjee and Duflo (2008) have
used two alternative absolute measures—individuals with
daily per capita expenditures of $2–$4 and with daily per
capita expenditures of $6–$10. By excluding individuals
who would be considered rich in the poorest advanced
countries (Portugal) and poor in the richest advanced
societies (Luxembourg), Kharas (2010) comes up with
daily expenditures of $10–$100 per person, after adjusting
household distribution data with national accounts means,
as the criterion for a “global middle class”.
Ravallion (2009) has distinguished the “developing
world’s middle class” from the “Western world middle
class.” To define the former, he uses the median value of
poverty lines for 70 national poverty lines as the lower
bound ($2 per person per day) and the US poverty line
($13) as the upper bound. Bussolo, De Hoyos, Medvedev,
and van der Mensbrugghe (2007) and Bussolo, De Hoyos
and Medvedev (2009) have defined the middle class as
those with average daily incomes between the poverty
lines of Brazil ($10) and Italy ($20).
Finally, Birdsall (2007) has used a hybrid definition
that combines the absolute and the relative approaches.
According to her, the middle class includes individuals who
consume the equivalent of $10 or more per day, but who
fall below the 90th percentile in the income distribution.7
Her rationale for using the absolute global threshold for
the lower bound is that people with consumption below
this level are just too poor to be middle class in any
society, while her rationale for using the relative and local
threshold is to exclude people who are rich in their own
society.
The above definitions are all based on consumption
expenditure or income. However, the middle class can also
be defined in other ways. Historically, in feudal Europe,
the middle class represented the group falling between
the peasantry and the nobility. Sociologists have typically
defined the Western middle class on the basis of education
and occupation in a white-collar job.
Since the objective of this chapter is to estimate
the size of the middle class across the developing Asian
countries considered, over time, it generally uses an
absolute approach. In particular, its $2–$20 range of
defining the middle class is divided into three groups. The
lower-middle class—consuming $2–$4 per person per
day—is very vulnerable to slipping back into poverty at
this level, which is only slightly above the developingworld
poverty line of $1.25 per person per day used by
Ravallion, Chen, and Sangraula (2008). The “middlemiddle”
class—at $4–$10—is living above subsistence
and able to save and consume nonessential goods. The
upper-middle class consumes $10–$20 per day (roughly
the poverty lines of Brazil and Italy, respectively).
===========================
This part is interesting too:
How do the above size estimates compare with others
in the literature? Kharas (2010), who defines a global
middle class as those households with daily expenditures
from $10 to $100 per person in purchasing power parity,
estimates about 1.8 billion people in the global middle
class, mostly in North America (338 million), Europe
(664 million) and Asia (525 million). However, because
per capita middle-class spending varies greatly across
countries, the spending shares of the global middle class
differ significantly from their population shares (Figure
2.2). For instance, according to Kharas’ estimates, North
America accounts for 18% of the world’s middle class,
but 26% of global middle-class spending. Conversely,
the global population share of Asia’s middle class (28%)
is larger than its share of global consumption expenditure
(23%).
Using $2–$13 per person per day, Ravallion (2009)
estimates the global middle class at 2.6 billion in 2005,
806 million of whom are from the PRC and 264 million
from India. More importantly, he finds that 1.2 billion
people were added to this middle class from 1990 to 2005;
the PRC and India together accounted for 62% of this
increase. At 62% of the population in 2005, the share of
the middle class in the PRC is much greater than in India
(24%), under Ravaillon’s definition.
Finally, Birdsall’s (2007) hybrid definition of the
middle class—individuals consuming the equivalent of
$10 or more per day but who fall below the 90th percentile
in the income distribution—produces some unusual
results. According to her estimates, neither rural nor urban
India has a middle class. The rural PRC, too, ends up
with no middle class, but she estimates 38% of the urban
population in the PRC belongs to the middle class. These
results appear inconsistent with reality in these countries.
