No cumple con indicadores básicos pero al menos con algunos de los indicadores complementarios

In the attempt to d e t e r m i n e an aggregate supply function for the country as a w h o l e , the h o m o g e n e i t y h y p o t h e s i s ( i . e . , that all areas of p r o d u c t i o n w e r e very s i m i l a r ) w a s rejected on all counts w h e n various r e g i o n a l c o m b i n a t i o n s w e r e t r i e d . Only three r e g i o n s , the V o l t a , C e n t r a l and S u n y a n i and p o s s i b l y a f o u r t h , W e s t e r n , indicated any semblance of h o m o g e n e i t y (see A p p e n d i x 3 . B ) .

B a t e m a n ' s C o n c l u s i o n s ;

The m a j o r findings of the paper include:

the importance of cocoa and coffee prices to the areas p l a n t e d ;

the p e c u l i a r lag structure b e t w e e n planting and b e a r i n g ; the importance of rainfall a n d , to a lesser e x t e n t , h u m i d i t y ;

an inference that the growing season shifts as one moves w e s t w a r d across Ghana (because the rain-bearing w i n d s hit Ghana first in the w e s t and then move further

to the east later);

the d i f f e r e n t i a l response of output to lagged cocoa and coffee p r i c e s , attributable to the different s o i l and age s t r u c t u r e s ; and

f i n a l l y , the b a s i c conclusion w a s that it w a s folly trying to estimate an aggregate supply function for the entire forest zone of G h a n a .

3.4 JERE R. BEHRMAN'S MODEL (1966, pp.712-714)

Behrman built this model for each of the eight leading cocoa producing countries; Ghana, of course, being one of these. He

acknowledged right at the beginning that his model was drawn substantially from Bateman's model. It is therefore no surprise that the two models are so similar.

The most significant difference between the two models is that Behrman prefers the assumption that the desired area in cocoa trees in

the t^^ period (A*^^) , is a function of the producer's real price

expectations held at the time t both for cocoa and for the alternative crop coffee, compared to Bateman's assumption that the actual area planted in cocoa is a function of expected prices over the bearing period of the trees. Behrman's investigation of the cocoa supply function then proceeds as follows:

where,

A*^^ = the desired area in cocoa trees in the t^^ period. PC ^ = the expected real price of cocoa in year t.

PCF^^ = the expected real price of coffee in year t. Equation (4.1) above, states that the desired area in cocoa trees is a function of the producer's real price expectations held at time t both for cocoa and for coffee.

The actual area in trees at time t (A^) is hypothesised to be a function of the desired area in trees, formulated as (4.2) below:

The expected real prices of cocoa and coffee over the lifetime of the cocoa tree are hypothesised to be a weighted average of all actual real prices.

P C \ = a3Q + P c S - 1 + - ^ V l ^ "3.t •••

= ^

P^^Vl

+

^l^^C^Vl

where,

= actual real price of cocoa. = actual real price of coffee.

In order to conserve degrees of freedom, a^^^ and a^^ are assumed equal. Equations (4.1) to (4.4) could be manipulated to obtain the current area of cocoa in terms of observable prices. But since no satisfactory time series data for area in cocoa exists (for Ghana), subsequent work was based on quantity of cocoa actually produced (Q^) assumed to be

thus:

00

where,

Q^ = actual cocoa produced.

y(i) = average yield per unit of area i years after planting. Equation (4-5) above, states that the quantity of cocoa produced in the t^^ year is a weighted sum of all past areas planted in cocoa, in which the area planted in the (t-l)'"'^ year is weighted by the average yield per unit of area i years after planting, y(i). In addition, this weighted sum must be adjusted for possible responses in husbandry to

real cocoa prices lagged one period and to possible responses in harvesting to current real cocoa prices.

The infinite sum in (4.5) may be eliminated by taking the first difference, relying on an observation that the yield of cocoa per unit area has a distinctive pattern. This gives us:

AQ^ = + {y(n^) + ^Sl^^'^t

+ ... (4.6)

Yield Pattern

Yield per acre is negligible for the years immediately after planting and then increases abruptly to y(n^) in the n^*^^ year to what is almost a plateau. The yield per unit area then may increase

relatively abruptly to y(n2) in the n^*^^ year to a higher plateau, on which the increasing yield per tree is offset by the loss of trees. The estimate values for n^ and n^ for the leading producing countries are given in Appendix 3.C.

Finally, to obtain a supply expression in terms of observable variables, equations (4.1) to (4.4) and (4.6) may be manipulated to eliminate and as in (4.7) below:

AQ^ = 4- b^AQ^,^ + b3APC^ -h + b^APC^,^ +

... (4.7) where,

b^'s = algebraic combinations of the ai's and y(n^) and y(n2).

Estimates of (4.7) above are shown in Appendix 3.D. U^ was assumed ' > t

B e h r m a n ' s F i n d i n g s and C o n c l u s i o n s ;

T h e r e e x i s t s a t w o - p o i n t i d e n t i f i c a t i o n p r o b l e m b e c a u s e the a d j u s t - m e n t c o e f f i c i e n t s a ^ ^ and a^^^ e n t e r e d the d e f i n i t i o n of the c o e f f i c i e n t s of the e q u a t i o n (4.7) s y m m e t r i c a l l y . T h e signs of the e s t i m a t e s

s u g g e s t , h o w e v e r , that at least one of these c o e f f i c i e n t s (and b o t h for N i g e r i a , B r a z i l and the D o m i n i c a n R e p u b l i c ) is g r e a t e r than one in

v a l u e . T h u s , o v e r a d j u s t m e n t in p l a n t e d area o r p r i c e e x p e c t a t i o n s s e e m s to b e the p r o b l e m (see e q u a t i o n s (4.2) and ( 4 . 3 ) ) . H e found that his e s t i m a t e s did n o t e x p l a i n the v a r i a n c e in p r o d u c t i o n as w e l l as did B a t e m a n ' s for the r e g i o n s of G h a n a for two p o s s i b l e r e a s o n s :

(i) the failure to i n c l u d e i m p o r t a n t w e a t h e r factors b e c a u s e of the u n a v a i l a b i l i t y of d a t a , and

(ii) b e c a u s e of the l e v e l of a g g r e g a t i o n at w h i c h the a n a l y s i s w a s p e r f o r m e d .

B e h r m a n , h o w e v e r , c o n c l u d e d that his e s t i m a t e s s u g g e s t l o n g - r u n p r i c e e l a s t i c i t i e s of the s a m e o r d e r of m a g n i t u d e as those w h i c h B a t e m a n o b t a i n e d .