CHAPTER 8
Problems of Modelling for DecisionMaking
=
'I'h.,. mod.I.Ol' ....d to.ld d"''''''n-m.akiI\J, '''M' than 10 .d..
",,"nunc
re'<I",h. problmu IllS< in prooidinl the mod<lIm with. nIitabl. wo,kin,
m.y
.ovir"""",ot... w,1l .. io differ.nt upe"t. of mod.llm~ m,<h<><l"Iov,
.bo l>e diffi,ult;'. io '"'tiring that m<><l,U." c"",muo",.l. ,rrectiv.ly wrth th,
d.doi""·rno.k,,, Ind wnh <leh 0,1>0,. In thi. eh>pt.r ....'. try to identify the m.in
p,ob",," in 'bno .."OUi fI,ld•• IncI drtw particular .tt.ntion to sp.cial problem. of
do,~lopinl""",ntri...
Th,,.
8.1
PROBU~IS
I" .\IODEL-BUILDI:\G
~IETHODOLOGY
II. have bri.fly """.idered the ..riou••pp",",h.. to the problem of buildinJ
.,,,i,,,,,,,,,,n1l] "",uu""" mod.1I (_ Soctlon 7.3), It ohould l>e emph..ized,
however, th.t ,ovi,onm.o,,1 oint"l.tlon i. I "lalil,.ly n.... lod ..pandirlJ fi.ld of
re...,,,h .nd. while ,h•••i.ung .pp'ooclr.. p"",id••yot,m"i" ....y. "f d...I"l'inl
t!reIe mod.b. thO)' ar' nOt fru from Iimlta"un~ In thl••ectlon_ w. will dlscu..
"""" <Sf tho more Importont of th... Itml..tio,,, alld tho kind of pitfall. optTl '0 the
un... ry mod.1 builder,
1ll.1 Do.. Req~"",n"·
On. of the 1IIC>1' difficult probl.ms f"'in, lh••n"",nm,ntal mod.lItr i. til•
•vaillbllity of Ipproprilt. da". Th. fi,ot .top rn hi. '""'"iaat;on should Il'O'ly. b.
an evaluation "f exloting relev.nt information "" th ••yll.m. In all its fonn.. S<>me
c<>ll..,,;on "f prelnn;nt'Y d..1 rno.y l>e n«....I)·; h"",.,,,It. it I. imponlnt to note
w, """rtsivo data sh"",ld be rolle<"d ooly afte' tho p,oblem loci its mod'Uint
requrremtnlS Ita"" l>e.n ..,.Iulted. In f"'t. 'h' p'oc.... , of mod.1 btlildinl and dllt
colltctiun should inrt,act ;terat;vely. Thu••• prettm;n.!)' mod,1 mlY b' built usirli
exist,nl dat•. and d.nnlnl th. n.w d... which would l>e re<julred to pennit .n
improved mod.1 to l>e butl'. Thi. wonJd in tum don", furth... d.", "'qui",,,on".
mil the procm would l>e repelled "nt~ further rorlrtm>enu oppe>r "nju,"n'd. A.
we hive ...,. ;" Ch.pt" 7. it I. not u.uolly poI~blo to perf""" planned
expe,,,,,,",, on 'ho r"l·lif, .yortm. Ind tho m"'t thal "an oo""ally b. hoped fo' i.
the collection "f dat. dunn, ilS norm.sl operation: but. tv,n if th~ iI pos.siblo, it
... ""'" .,t.....
tr."""n' .r
'h" ""l>je<l i'
Ji>on
Environ""",1 Imp", ",,,,,,,,,,,nt rscon. j 91l.'
In
.<pro"''' 1 or rho seon R.pon 0.
"'ill "'"oUy be difficult. Thu,. to 'ollect dolly da.. on "'en 'h, majo' indbto" of
",'at" quality in a ,I.. , .y",m for an ,,"nd,d porio<! of time con h.
tl""',on,uming and c",'ly. Th. d... mu" olio. of 'oU,,", l>< rel.-an, 10 ill.
'P'"fk modelhllf problem, n",hina I. mort f""tratlni 'h.n to b. p""nt<d with
nc,
'h,
an <)IC<'~" amounl of data. only to find thot m",' ofit h.. littl.
p,oblom" hand,
Th. probl.m. of data coll.ction. includmg tho lack of adequ"e m..'u"m.nl
"chniqu. . .nd "n>o", CO" make It diffi,ul' to .upply an
,equire<! data_ For
<)Iompl•• biochemical o'yaen d.mand (BOD) uk.. four day. '0 mO..\HO and thu,
tan inuoduc< ob,iou. problem. if. d.ily mod.1 fo' "'at" quali'y i. require<!. In
'uch a ,i'u"i"", mod.lI", ma~' 1>0 "mpte<! to procee<! ,."hOUl odequ'" da,. 0'
proc.du,.., lhi. con lead
inad.quat. mod.i, and a ,.nden,y to t<gard the mod,1
.. ,h. '~~"m i,..If. roth" lMn .. In appro<im." m.,h,mali,,1 repre"n .. 'ion
.ubjec, '0 unewalnty,
,.I..... '0
,h.
'0
8. U Seal" T.mpo..1and Spatial
In man,' .n_ironmenlal .imuJalion moo,I •• moot of ,h ••,,"om .... rLobl.. yory in
'paco ""or the g'Ol!"phio .,.. under con.id""io". '" ,hoic. of ",ale ofl.n h.. ,o
be mad, and there may be btll, information ..ailahle 10 !,"id. Ihis ,holo', It i'
p"uihlo 'hot an """all coll.ction of parli,ulars into on' aUrea'" "'ouldl.ad to
"Ita! poin" l><irl/l mi,m. "'hll< '00 d'lalle<! info,m.,ion could mah tho modol
impractical. i" lerm. bolh of modelling and of d... colhtioo_
o.p'"ding 00 the oature of 'ho .lrnul"ion modelling obj",",.. , 'ho modol may
require diff"on' timo ",al", For .xampl,. lh. p,oc'" of conl1ructin~ an indu"',,1
compl" 'wld ca"" imm.diJ" damaa' to ,h. looal .nviron""n', wh"e.. tho
.ff<ell of pollution from thl. ,ompl.. may tah .<V"aJ yea" b.fore th.y become
"gnificant, AgaJn. ,h. loog.term """"te I<vol> of water poUu'ion OlO" be
..'i,f.otory fo' pouble w:"" .upply. bu' thi. i. no' much ,omfo" '0 the fiob (or
lh. fiiherman), fo' ,x""pl •• 'ino< obOr1·t<rm violation, of wat., qualily ,an cao"
ex"o,i" fiob kilt., Th"e kind, of problom. C,," be ex...,bated by f,;ling 10 defio.
suffioimlly well 'be objo,,,,.. of the study at 'he ou,,,t,
"'nOlher p,obl.m ari>ir\i 001 of lhJ' nud <0 d.fin. lb. Hm. "'... "refuUy Ii., In
th. ,on"r"'t;"n of mod.l. 'ltal m.y ,on,.in 0 mlx,u" of bthaviou",1 OSCdiJllOn.
with wid.l;- diff,ri08 natural f"quenci.., Mod,l. conl1ru".d in lhi. man"" c.n b.
'Ubject 10 ,ompUltlionai p,obl.m>: for inSlon"". th. in1<8,"lioo of ,h. "'t of
differ.ntial equation. (ofteo tetm.d -Iliff diff"enlial .qualion,) d.""ibin. ,udt a
~~"m con raJ.. m.n~ difficultl.., A pta,tical ..""pie of mi. 1m" probiem o<ou"
in the solution of numorical model' of the atmosph"•• ",·h.,. sp<oi.1 procedure'
.,. ,equi,e<! to .Iimrnato ~,.,i'l' w .....
8.U AW<illion
'0'"
Wh.n d••lirl/l with larg' envi'onm.n'aI,y.,.nu;1 i. n."",,"ry
"'heth" me
require an aggrogal' .... cro ~mui .. i"" of lht .yutm or whethe,
roo.. detail.d micro informa'ion i, d..i"d. In the fin! cal<. it i' n."",.. ry '0 define
lbe mw,1 in t~rllll of lw~gall't mtlbkl, Thil ~~elci", Cln lOmelimei ~ o!>l'lollf,
as wh.n biocl\"nical oxnm d.mond i. ustd .. 0 macrO-rot ..u," of tit< oxygen·
modollin~ ob;'<ti..,
.!>sorhilll pO'eJl'i>l1n • ",..m. How."'r. it ",",y'" difficult ... when On. a".mpts to
d.fme 'n oveun " .. «r"'luality index whiell includ.. 00' only o'n,n..b'",";",
pot.ntial. bul .Iso the p......,cc of nutrient>.nd 'oxic '''"''.noel- This difficul'y
arisei beow in llullitiution it Une""lSlIry to d.r,,,, tho ,.llli.. ".'Ih'in~'of tho
diff."n' ",d.blo, in ,h. index.
In ,he second C"', i' m.y be difficult '0 product .Iorge mod.1 wnh m""y " ...
""riabl..... compl'" entity. In .uch. si'ultion" I,o'''n advi,""l. to d...lop "'.
mod.1 by d"omp<>oil\i it into. collactlon of in«TConrt<<l.d .ub.",<><I.I<. n::h of
whkh i:I simpl« '0 h.ndl. ,h.n ,h. 0 . .,,]1 m<><l.1 >od c.n b. fairly ""'ply
<""nacto<l ,"ith ,h. mh.r 'uh-model' 'hr<>ugh ..illy d.nn.bl< In,<,f.ct, with
compotibl. input< ""d OUlpU'l- Such mod.l dttompo,;ti"" ."" orten b. ",comph.....d by "f...nct '0 ,h. phy>ic.1 nllu," of th. ,y".m. whi'h m.y i,.. U h.
Simil.rly con,id".d In wh.•y".m term., A1temllll·.ly. ,h.,. ha.. b«n .tt.mpts .,
'j~,<mati, me,hod, of ,y".m d.''''''l''''i,I<lfl; bu, 'h,'" do no' ..""
hIV. b••n
patti,ul..ly w ... tsful in pr",'''•. ""d ,h." i' an urgen, need for further "",oreh
in
or.a. FUllllj'. i' em be helpful md In"ru<ti•• for decr,ioo-mak." to
'onsid" 'ho diSlAr••md ,ub·mod.l, in '.rm, of • hier.,<hy of d,ff".n' lev.b,
"';,h lh. upper 1"'e1' linkilll wllh the 10,"'" 1....·.1.. lIld WI'" p_iOl. 1mb or
toordin"ion bel,"un ,ub-,}~"m. at 'h. ,.,.". k".I.
'0
'hi'
8.1.4
In"rr.en bet,"un S"b-!Ilod.1s
If ,uh-mod.1s or. constructed In • 'tmIlar m.""er. ,h.n ,h.r. Ir. oft.n only
minor probloml of Interf.<:illl them. If, on ,he o'her h.nd. ,It< p'''I"mm.' ".
differ.n' in some ..n... nuny probl.m, <In "I.. - «",ioly too m.ny to di"uss
her•. Th. prohl.m con h. min,mlzo<l, h_••• r. hy mo,n"mlng ",n"'n' communi·
c"i"" bel .....n ,h. mod.1 builde" ""'sid<ling ,h. wb"y".m' (should ,h,t< b-e
m'lt. ,h.n on. pa'''"PI/l' in ,he mod.m", .xer,is<).• nd .n""i", Ih" "I<
"..i.bl.. pmi"8 'hroogh ,h. 'n,.,f.u m ",.11 m.t<h.d. For ...mple, if tim.·..
., on. 'I"'" 1-<.1••" Fner...d '" "", ,ub"y".m. ,h. O"'PU' of 'h" 'ub .•y".m
intO '''''lh.,
diff.,..", 'i"'" 'cale should 1>< m,d. ,omp'lihl<.
ri.,
"sin,.
s'1,S V.lm,l""of!llod.k
Th••,lid"i"" of ,h. mod.l-I.... ,h. m."Iu"g of 'h. mod.1 ~ith 'h....i
,ymm _ i' p.""ululj· difficul' In ."l'ir""me",,1 "ud..... In "fU<lurin~ on
.ppropn.,. mod.l. i' i' of V'" Impo".nce '0 m<orpo"" ,h. b.., poosibl.
Ufld"'tand;ng of ,h••n""onm,nn' ph.n"",."" V,lid'tio,,;, lh.n lh. n.xl SlOp. It
...I",..y, ...." ... 'Y '0 .,ym.. 'hal tele"I/l' d.,. Or< ,olie'''d .nd us<d fo, 01.
pUtJlClSO'l of "",;d,,ion. 11"'oulh I' m.y b-e diff"'ul, 10 d.n... which p.'" of "'.
mod.1 req"i" be"., ,·.Iid.""". On. populo, .pproa<h 10 thi> p..oolom i' 10 us<
.."';t;'i'y .n,lj"is '0 ind,<,,, 01_ portio", uf the mod.1 wh"h h.,. • m.rk.d
.ff." on ,h. 'Y',.m
'nd ,h". should b-e p,,"oubrly <.reftlily ,·.Iid".d. If
i' pr"".. im"",sible '0 coil", ,he r<quiJ<d d... d.frno<l i" 'hi> m.n".r, the
"'"1""1 un,m.i"' .... "'ould ./w.\" be "ol.d c.refully in Ih. pr...
oh"y
","I" '0 ,h. d"ision·m.~<r.
A mod.1 of ,,, .n,iroo"",ntal ,yst.m 'on b•••hd".d only ~'Ilhin some
pre",ribed limits of u"","in'y. whldlln '"m "",lIlimi, lh•• <,,-,r"'y wilh which
"'poll"
""'ion
dec",""" bOlt'd on tl>< model m.y bo m~. A••'. h...·, ..." In C1Iaptt". thlt
dilrl<U11)' .ri
III ",n. bo
rm,""""'nul I)'n.ms .,. ..,.,.".",., Ilth...
ilJ.d<flned ond
til< ......
c.. bo
campi"". Simi"', p,olIlerns b .
...",nod tlIo o<ooomic II>OOU: b.ild<. (or tNtl)' r
Tb<", iI d •• rIy. hooo-·.... t •• n
"'F'lt no«! for """" tII
t........",k 0fI til
tIm.non ""d ,'>lid.."", ofo.odolJ
for WJ< """'Pk'< S}
otld 1ltt fut1ll<t inYlll>.....", of
th<m:otoc>l , .." ..
I><1UlI ... ,m ... 1md 1>Dd
of .... 'Y"'P"th,· for I)
"""..,. nu.
'"'IUHftIIOnt r : - . bo "'
"...-.d. tho d.f"""QC><S of no",,,' _.II"on
1Ilod.1''''lI in tIDr. trOJIK' ..... c....,.1lIl>1< "..s «><=ll'. . . .""" iI u,.."dy """",t<l
If
-ibJof' .."Ill ph)~~..--< ''''''''''0110
t
txt"'.,...,.
.:nulI'''''''
"'..... ttl c~;bWtl.
1.6 TI
r
_.ef-"
"..r...... _
s-Jatiool """"
' IN
J>O'O'Pi< or orpmz.,- ...
........ of
>lid tIDr.
Iud to ..- . problerns. Fm'. II tIM I8<>dd 01 10 k
-.I b) 1ltt re<lponl'I fa< oppl..-.t_ 10
_
S}.."""- ""'" tbo
,.. pfCb..", ..
to ........ tha' ,
<omputt,) is
nrudob..
<lnl1l _-...at}'
th ,f th.
lIIOd.l i. In 1ltt form 0( • ,'Mlputt, ptOJrmtnX. thou " IS .-p.. a.I< "h Ihf
eomp<I'<r
lIS<d 1» ,Itt
til..
du......
• qj].blo. Third, rt " _
""portln' til" .... "'''Pit" un<l<"'"..s. til. Utoo,
hm,ti""i,... of 'h, mod.1 or p'''Inm",.. til 0,1><, .. "d•. h"",'" WOrlr.L F,,,.lly. 'h.
_j"
'0'_
__.-. , _ CU._'_" ..
_ 0'
",''!*ft' ...
'j""'"
'0'''''''''
odoq"", "......"..., (..
mod,1 may b< """".,.. d,,, ,.... m...no, .1,udydi"u....J bu' for".. III r:on"'''roo
"';,h • ZO"V,ph",olly ditf.ron' bu, .n.IOIo,,, '\ po of .y".m ' .. ' bo,"u"
"o»,,"mo of d,ff","' ')1'"' (th. La. 0..." BLvm. mod,1 war .ppllO'd to
,""""" ... 'undra by W"lg<>I..... ".1, 119751). In Ih" """. ,h<r' .... of <"uri<,
""'n) pi'i.lI•. In .dd",,,,, 'Q ,h. ~OII\t\'l~n","i"" dlm,~It,e. 'ltm i< all.<> a
'0
,n'u" tha' ,he ,nodel i' ",,:ida ..d ;n th. no" c.... ,e", 'Ithoug/1 ,he eX"n, of
,,,..Iid,,;oo will d,fft! d'p<n",". uJ'OO ,h. d"um".nc<I, It I. unhkely, In 0,10.,
'ha' a truly 'rJn,f.rabl, mod.1 w,lI .... , b. J"'eloptd except und...'1)'
",",,;11 ci"umo"n,..,
Ano'he' Imp<><unt poln, .., ..d,,,, ttlf1,f.",b,lit~ reb.., '0 th. d'S". of
F""'oI,l.I1lOn, Th. 1l'I<>d.1 bULI;l" ....... Id "'ornp" campro,,"'. bolO...." ' mod.1
i' '00 1'"",1
th.,ef",. '00 oomplu....d"". "'hidl" too ""<1f,, ""d
>l!o.... applJc.ouon
1ca."",. th.. <f.... 100 fully ,..bzO<l
On< of .... IIIOS' ...1dup... d <ommunlCllnon problem>" th. b<k of Ill
,.
<Io<"",""Ul1Ol1 of roodolL lood<qll1tt <10<""""''''0" of tho COOl.....' .... b
.
I ,,,
and "9",...... fo.. " ... of m,'JotIs p..... en" pt<>ptl" u.. b)'
·rmto
"'OIIuJ
of """"10 '0 ......"tWIOOL
".0<1
"""d,.
""'<to
ar..s
por'"'..
_,om.
*"....
"..r.e
.2 PKOBlDlSOF PRO\IOl'G A SClTAILE E"'IRO''lE'T FOR \tOOEl
II:IlDERS
,. ",.... Ius .....baiI
...... """"". ...
of .... _
...,.,....., dlflkulun
In,,,.-
_f"""q a -.l<! buoU<,
' 100 ~ .... f.pa1O<L If Modol
. . . . . . Of< ";-..ablo t, 'Iv
' .. nl pgk;aorh,,~,~ "'....."ao,.
Iio< ... l
bo Ift»<d '0 _U) tbo Il1<l>JoI and . .) fM" dlff"uh «> of'., tho
'...,. !hal
prof...i<>Il.1 in"lri'y "oold die,.,.. In 'hn ""no,xion. ,h. mod'll" ...d. ,h.
support of an ,x1<m,1 Ind imp."i.1 body wi,o .offici,n' P"''';ge !<'
as .n
I1hitOl,
.,:t
On~ CUI ~ lllo n.~d for an ;nl.l'ftanonalac.dtrruc body ••dequ"'ly .l.ried .lId
"IuLpped. whose prune funooon ;. '0 eoo,d,n." 11>, IonS'"'''' planning of
mod,liI.. in ,h. field of.d.ne< .nd te<hnol~y Suoh I body mishl indud< .monl
ill fun«ion. lho.. of odjudgJnl 'h' 'olu" reliabili,,' .nd .pprop";" ..n... of mod.ls
it by p'ospe"Uv. u..". 'nd '01inl ••• C<l<lrt of 'pp<ol whore
.ubmiued
diff.r<nCd Ifos< be'.... n mod.II.,.nd mod.1 ""L
'0
8.3 PROBLDtS ARISI\:C BETWEEN
.~tODELLEI{S
Al'D CLASSJCAL
SCIE:-'TISTS
It cann"' be d<m.d 'hat It ,h. p....n, Um. >om< so.. nlim rem.in uncon"",,,,,d
of ,h. true "'onh of 'y",m,.mod,llinl 1<ohnlqu,. Thi. 'l1i,ud, h•• "".n
,n,"uTII'd by .x.mpl" of bad mod.ilin, .nd mod.1 .ppl,o";on, .nd by
mi.... p'''.n'''ion of ..'h.l mod.ls e.n df'Oli".I)' ."eomph<h, Furth.rmor•. 'h....
h.o.. "".n inl1In"". in ,,'hi,h mod.l, w.... d.veloped b'wd on '01pi,ieol d.,. or
ou,dared 'hrori" .-her< much b"", ,hoo .. 'io.1 bookg'ound w", I..il.hl,. A••
...ult. diffie"iti" m.y "" .n,ount<red 10 oo1lin"'g rho "'hol• ./l.",,d ooopelltion
of p.nicul., 1'0"P' of >cion"", ..·hn« .pe"i.li..d ~n""·l.dg. m.y b' 010" .:oI"able
for indu.;"" in • mod.l. h .. when eoope"ti"" " fo"heomin!. diffioulti•• c.n
"UI .ri.. ""'.n scien'i'" ,.nd '0 insis' upon plO'o'idina more detail than i. requiled
for
limited purposes of
mod.l,
,h.
,h.
8.4
CO~I.\IL:"1( ATID:-'
PRD8LBtS 8ETI\'E~\ DISCIPLI\:ES
In thi. oro of in'1<.~ngl) nl""'" 'l"'e"II<:."on. ,her. con b. diffICulti•• in
..I,bli<hing ,ff.cti,.. 'OOP<"""" Ind <ommu"i,,""" ""tw«n .~peT" f,om
diff.,.n, di'dphne' "'ho h.,. differ.", "oncepts. l,nguoge, .od ..,.J. of "'phis,i".. ioo, Enoi,,,,,m.nlll p,oblem., how...,. kn",,' no di>c'plin,ry I>ound.ti...nd .
.. ,h. insLgh" p'o"id'd b~ .~.t<m. ",len" m.k. d.". ,h. d,ff....n' d'''''phrtlr)'
,nterao' and c.nno' ...dy "" '>olal<d f,om ..,h o'her. Thu•.•n.ironmen,:oI
001"11""" mod,Uinl will u.uolly d.mand "'y dOi< eoop<r>'ion 'nd 'ommuni,.,ion "",w••u. "lti.l¥ of "pe'" in differ.n' di",'plin".
Th. prool.m of ,ommunicoli"" i. p,,'i<ula,i~ ..' .." be'w... thoo< ;n the
ph}'>i"ol
,h. "". 'X''''''''. and those in the "",..I "'''nee''' ,h. other
(8i''''
1915bl. ~'"Y ""'iol iCion,i...." not oc,Ul1o"",d to expre,slOe ,h.ir
hypoth
in qUln" .."'·, form, lnd"d. some 01') '''n b. ,.lllIIoni"ie ,"""d.
qu.n'it.,i.. """hod. of In¥ ~Ll\CI, r..lina ,h.. hum.n b.h,viour, fo' ...,.,ple. i. by
its "ery narur. no' quan"n.bl••nd difficull '0 predict. To >omr ,x"'n' their
objee'ion, Ire b.wd on m"undersl.nd,nl of ,h. ,..,"", for mod,UJn!!t«.u.. of 'h' diffieul'i" in ob"ininl 'h, ",hol,".."ed in.oI.""'.n' of.lI ,h •
m.~'
•pe'i,li." "qui red. 0' of oh1Olni"l I' wh.n requireJ. prof.";on.1 mod.Il
oom<';mr. "" «"'P'ed to .... 00' lhe n«....ry kn......ledge fo' 'h,m..I, Thn i.
r.p.mble, e..n 'hooPt
modell.,,· uncl''''andlO' of .~~'<m,.11<1 flmi!iln'y
wi'h 'I-.r r,,' of 'I-.r mod.1 m.y be I""" ,h.n ,h., of 'h. lP«ioli" •. Th, mod'llm
should no' proc.ed '00 far without 'h, proper P"""'po"on of In the rd.,..,."
.ped.li.". if In 'pplOpri". "and.rd of .;mula'ion mod.iiing i' '0 be ",hie".d
..pe,"
"'1<""", ..
,h.
85
CO~L~IUNICATlO" PROBU"lS
BETWEE" \IODHLERS AND
DECISlm':·!otAKERS
Th. t." .nd m'"" ""10'" probl.m ."'0 in m<>delhns for d.".;,,,...'''.inl Ii.. in
th. in,,'oclion bot",..n ",..n"'" mod.lIon .nd mon","" d<"isi<m-m.k..... Th'
often di'!"T". ".inlng. p<rspt",.,s, 1",,1., .nd "",,,d 'jmm, of th'", two
",<JUp'. . . d... ,ibod in (hopte" 5 'nd 6. m,y p",,,,nt b"'i'" t., rommunicall<>n
and mntual undmtaJ'ldlnl. ond 'h'''by l,m;t th. 'n,,:'" of mod.1 .pph""ion.
Communic>ti<>n problem. ". ""nif..t " ",,,,,.1 poom in tho pro«• .,f mod.1
.pph"ati"".
In man~ in"m«•. decioi<>n·m.kn. ma~ no, h< hu. of ,h. po"nll.1 of
limn loti"" mod.lIin.
ao1 ,h. on.l~sis ond .~ntll •• is of policy oJ"m.ti'u \Imy
decision-m.k." a,. oc<:uS!omed '0 ,,.ditionoJ p,obltm-solHnt 'e<:hniq"... nd nu~
"SIS! ,)[
n.... ,echniques "",h., .imul.bon ",od.Uil\i. Thi' i' P'r1i"ul&,ly
in i,.. d••,loped "oun"i...
At .n.,th" I••• L it is impo,un' llu' bolh mod.lI." and d.mlOn-mak", sh,,,,
«>rnmon defln,,,,,,, of the .n.u""menul p,oblem at hand if. mod.1 ;, '0 bo u.. ful
in Ih. decision p,"".... Failu.. ;n1<'''''' .d"lu.,,1) from ,h. bqinnin. of mod.1
d,velop""n, c.n ,..ult in • mod.1 th" "dud" f."o" "'hich .,. of criti,oJ
polio~_rna"nl or provtd. ,..ull, ",In,h .1< only of inl"'" I.,
importon«
lhe sc"""rl< ....""her. but ,tllIppr.,priot< or ",.Ie,~nt w ,h. de""ioo·
'h" mod<lle" h< .,,'or< .,f ,he
makinl li'UJ""". Il is .Iso impor ..
deci,i<>n·m.k,,,· 1",1, .nd obj<'".''' in m" to 'n'U" mox,mum nlility of til.
mod.1 ""'POl. D<d,ion_mlkJl\i ob,.,,,... ""ould be ".ted IS ",II .. ponibl. It til.
h<l'nninl, witll ,h. "oli,.,ion 'hit fo,,"ul.uon of obj<'"'''' i•• n it.",i". p,""....
h shoold be t<C"!"i .. d
,h. d.finilion of "",i'1>1 ohj<ctiVfl in the d.cisi<>n
p,,,,,... IS d,fficult. In f"", loili .nd obj«"... ",oi". ,1"",ly in "SjIORI< to ,h'l\i"
in IHi,ud••nd pt,c<p,,,,,, of 'h. IOn"al puNI<.
rn ,dditlon to the probl.m, ."""i.ted with ,h. dd,nllion of mod.1 obj«livu.
diff".nt ,}'ptl of mod.l. m.y be 'ui..ble 10 'pt",f", d",sion-mlkin. ",'u"ion..
Thi' i'
wh.n • n.,,' mod.llinl pro;,,' i' h<in~ «>rnmissiOfl<d fo< 0 "",cifi"
problem, 0.....11 at wh.n 'n ,x"""1 mod.1 i, beinl ,h_n fo< Ipplhti<>n. F""o"
"",h ., "on",..n" "" 'ime. money, olld
at ",.11 •• ,h. inform.tlonal
n..d, of ,h. d<ci';on·m.k<r. will.1I .ff.,t which m<>d.l ."'""u,, 0' ,pp,oa<h i' the
most 'W,op,i.". Th.. "hoi" "'" be '\I<<:<"ful onl}' IfteT .ff<"". communlO"ion
h<lw.. n mod.I.,,, .lId d«ision-m.k<" h" Ia•• n place.
Foilu" of mod.lk" '0 ,ommun>:ll. '0 d.<isson-m••,,, the lim,to""". Itld
limplif~inl ...umption. of the mod.1 <In ,,,ult in "',
dins in",p""'i<>n' of
.. ,llllS. inn"'d .x.,.<l"ion, of the mod.I, .nd, u!Hm ly, loss of ,,,dibil!,~ fo'
til. mod.1 ond ,imui"ion mod.II,nl !n ren".I, Th. 'SlUmp'i<>n' 00 ...hich t!I.
mod.1 i. b.sed mult. of OOU"'. be d.arly <mphuized Ind " .. mph..i..d. and ,h.
<OI\seq""n,.. of on
inte'pr<lIlion of Ih. ,<sullS when lit< ..."mpHon''',
in..lid t!lould b< "."d, ~10'«>'"'' mod.l ""'pu' mull h< in a fo,m 'hot is
und"mndobl••lId u..ful '0 the dedliort·m'.<L In som< ,,"' .. 'hi' m.y uk. 'h.
form.,f a shird I'l\i"",, .. hich i. "om""'n '0 botll mod.II". ",d d.ciIi<>n-mok.n.
.uch "I'.phl< d'1pI'JI' or pmil\i..unulJ';""s.
Th. go""..1 p'obl,m of ....bl"hin5 ,h. d.mion-make,,' ,onflden« in til_
mod.l i' ult",utely most ,rudl!. be"u.. wi'hou' ,hi, confld.n« ,h. moder,
.-..ulll wiU n",,, bo in"orporated into 'h' policy-m.ki"l p""'.... "
'0
"ue
mi."u"
'0
'0
n'
'Iu'
"IS<
"'''''''''''1.
,tKOr,«'
d."i,ion-mak.r·' coofid.n", will bo di,.."tly .ffo,,«1 bj ,h••,1<n' 10 ",hich.ll of
the ."""'..,,><n<;on«l p",blem, 01... ,isf.«orily solvl'<l 110"'..... '. i' I, lik.ly 'hJl h.
will I>< P-Irti<ul"ly "ortcornl'<l Ihlt lho mod.1 i,., ,,·.11 voll<l."d u p<>Uibl•• nd
llul th~ ~xt~nl of this ..lid,'ion ~ ,nd 'he «,ultin, "ortfiden" he m'l'. ,h."fore .
• """il1' wi'h ,he model for«.." i' .Iw.y> repo<te<l "ufly.nd "o.mb,~"""sly,
86 SPl'ClAL PROBLEloISOF DEVELOPI'>G roU:-vrRIH
.xi"
",,,ie,
A' ,h. preO<fl' Hmo cerl.in id.otrfi.bl. probl.m,
"'hich
'he u.. uf
,imol.,ion mod.llrn!: in d<,·tlopin, 'ountrie<. Th.
of ,ho.. I, •
of
exp""" .nd ..,hnical l"'oonn.1 ,ap,bl. of d.v.lo!"nl ond impl.montinl
mod.llinl pr"",'" A l.«Ofld probl.m I, 'hor COIlIp"'" f.dlni.. m.y b<
!n.doq,.... Som< 'yp<' of mod.llinl pt<Jj<<t ,equU< quit< 10'1" <omput<r
1n".II.hort' 'uch lS're '''ely .,..il.bl. in d,,'elopinl ,oun"'" Admi"edly> i' i'
ofIon poo'iblo '0 d".lop .nd ",n. modol". dillon", but Ihi, h.. drowb",k,. for
in'er",11"" I><'w..n mod'lI" .nd d«ision-m,I:<r dUMllho mod.\.buddiol i, "ory
d."robl. _. I><tt" modoL .nd 011• • O.... <rinlth. d",sion<ll.k.,., need. mOf<
p'«:i..ly. i. lik.ly to r"ult .•od the d«i<ion-m,k" i•• Iso Iil:.ly to h.vo more
I>< produced. tlie d«i,ion"",.ker
conf,d...o in i', l\1Ion Iho pre<lietion'
may "'.nl 10 modifj' hi. propowi <oone of ""ion .nd will <>11 for predktion.
under ,hong.d ....umpli""., COMequ<ntiy. ,h.re .r< "",.id"ablo od''''nlqes in
hovinl: tho mod.1 p«p'r<d loc.lly. In f1<', modolbnl pr0J<Cl. ",liieli «lyon.
bill" .nd
"""puler ou' of II>< <nuntry
likely '0 f.iL CI"Tly. ,uli"" and
d."il may suff" from lirruted loc>1 f.cillli... but th.f< i. n"",. u..ful body of
.xpe,ionce wilh ~mut"ion mod.I, ((It
"OIlIpU"r1 to I>< d,..... upon
Th. us< of re.dy.made mod.I•• roth" th.n on.. bull' to ordot. m.y b.
I"rtieol.rly .dvonugeuu. for dev.lopinl ",un"ie~ So lonl: IS. model;' " ..""ably
I"n"oI, il may be .dapled 10 fi' a diff."n' ,ype of ,y".m••llhoulft ,h••ffort
which rnoy be ,equired ,hoold no' be ond,,"timot.d, 0 ... "mpl< of !I'''of, •
mod.1 Ir>nsf" " .n "O!Iymm model developed by Ih. US.lIBP 0..." B,OIlI'
prOl\rom"te. which " ... a<I>ple<l 10 mod.1 Ih. <0,,,,.1 do..r' of EIYPI (Ayyod.
1916) - and .•100. "i'h > mod."te d'I'" of Itmplif"'''ion. '0 'uo on • qUite
diff.ren' ond much mlOll., "'mpu", ...ilobl< in cano f... 5<"roo 9.4). In .U<:h •
""'st import"", 'hina i' 10 On'ure
all Iho '·a<i,bl.,
'0
de<i.;on, ;n ,n. dev.lopinl """n'ry 'r<, in f,et, .mbodied in Ih. mod.1 b.inl
"""'f,,«<1 - Of. if 'h.y .f< not .lr,.dy th'r<, 'hot 'h.y oon b. in",,,.d ~'Ilh"".
difficulty. At pre",n,. ,hore.re
f.", ...mpl .. of mod.I ".n,f"
Ihi,.•nd
. .<It in ,hi. " .. ,ho",.re "rll. numbe, ofprobl.m, '0 I>< ",'<r""""'.
Ou"o • drff"'.nl type of drff"ul'y in Iii. u'" of "mot.. ion modelli",
in d...·.lopin, countri" .,i... rrom .!hurt'll" of do ... To I>< 'u". dot. 00 ,h.
o.h""""r of ,he COlllP!" 'j~,em. invoh'«I rn en'."onmrnul pfOblem• •re
in,d«lu." 0"0 in dev.IOj><d lOCi.ti... bu' this problem i' io<r<.i<rl;o d.velop".
roootrl", b<c.u.. of the mu"h ""on" period for "'h;oh scien'ific "odie. h.ve b"n
in P'''5'''~ It should be .mphalile<l. how<'o'<r. ,h., I"k or dOlO i' nOI • "",und
' .."'" for poo,poni", ,n. d.velopm.n' .nd .ppli",tiOll of limulotion mod.;",
fI",
"'or"I'
'''r1 '0
,r<
1><""
"".11
"'''', ,h.
'hOI
"'h"
'Th.~
1ft
rbe
19'9) ""'"
1_.
~,,' ''''~'"ion of ..
",r",.. oti..
""",,\<>1
"I.,"",
Iik.
""',Oi,," to
_rb>' """"". (F"oI<,,1
1917,
''',", n " .......... ,Uho...' only ,,,.", dol' ~ .. < ''''''M. ot thot
,.
Even "..h.,e d," "t .p",. and I>ri,1} qUllitoti.t" .imul"ion model m.y make
b<tt.. UI< of .~i"j"J information th'n tho owa! intuit;" ••pp'Q""h ,Ilh"",gh th~
"fino'
b<
&",,,",••<I,'nd ca" mUst bt tlktn ,o.void m''PI,,<d connd""". For
mod.llin~
po,,,,,,... ,h, d.l. will 00«1 (0 b< m>d' <I,nni«. P'trh.p....n
qUintitlti".; but ,hi. 'ory pro<.... of 'OIl ..'ling lh' VlfUt and qu.litotil', into the
prod$< .nd qu.ntitative '1',11 b. ,-,Ju,bl, in dir,,"ng ."'n!ion 'Q 'h, gap' ond
inadeq...d .. in .xi."n~ infonn>tion. Th, mod,1 c.n then b. expto"d to provide
,h, ..." prtditlion•• v,ilabl•. gi'-.n 'ho pro..nt .".. of unetnain,y. lrl<l ., ,h.
IMtIO 11m< to IO,io.. lo.... ub",!",nt
<oll''''ion.
d".