What Kind of Fool
Am I
What kind of
fool I am
What kind of mind is this
An empty shell
A lonely cell in which
An empty heart must dwell
What kind of
growth is this?
It is common to express growth in terms of a Compound
Annual Growth Rate, CAGR. Savings accounts,
loans, mortgages, inflation, and the Gross Domestic Product of the economy are often
expressed this way. This implicitly assumes
that growth is geometric and follows the formula:
Future= Base *(100%+CAGR)^(periods,
years, between future and base).
This is considered a marked improvement over assuming a
simple growth rate:
Future=base * (Period,
years, between future and base)*(100% + simple growth rate).
The compound rate is also called a geometric growth
rate. It assumes a constant, but
non-negative, growth rate (first derivative).
A problem with continuous growth is that it can surpass an absolute
amount in the future. An equally valid
growth rate is exponential growth. It is
more commonly encountered as radioactive
decay with a half life. For growth, the mirror of decay, the rate is often
expressed as a doubling period. Exponential
growth will approach an absolute but will never exceed it. It thus has a variable, not a constant, growth
rate (first derivative). This is consistent with a constant rate within an exponential function.
Future=base*(100% +exp(rate* period, years, between base and future))
where exp() is the exponential
function.
Over the short term, less than 20% of the periods to the absolute,
there is virtually no difference between exponential and compound growth. Exponential growth is higher than compound growth,
but less than 5% higher, over the medium term, 20% to 83% of the periods to
the absolute. It is only in the periods near
the absolute ( 83% to 100% of the periods to the absolute), that the exponential
growth becomes significantly larger. However
unlike compound growth, its future value will never exceed the absolute amount.