Sylvia Nakanyike
Makerere University
First Bio-Innovate Regional Scientific Conference
United Nations Conference Centre (UNCC-ECA)
Addis Ababa, Ethiopia, 25-27 February 2013
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 Scarcity of quality planting material is a key constraint
affecting sweetpotato productivity in Uganda (Yanggen and
Naggujja, 2006; CIP,2009; Hagenimana,1999; Kapinga et
al.,1995 ).
 Yet, use of farmer saved planting material is associated with
the spread of SPVD.
 SPVD caused yield losses of up to 90% and disappearance of
the would good varieties.
 Fortunately, biotechnological initiatives (e.g. TC and virus
indexing) are now available that could be used in rapid
production of virus free sweetpotato planting material (PM).

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 A sustainable use of such initiatives will
depend on farmers’ willingness to pay
(WTP) for the virus–free sweetpotato
vines, whose price will certainly be higher
than for farmer-saved PM.
 Thus, use of QPM may have a cost
implication which could make the
technology less affordable by resource
poor sweetpotato farmers.
 And, adoption of QPM will depend on
farmers’ willingness to pay.
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Major Objectives: To assess farmers’ WTP for
Virus-free sweetpotato vines
Specific Objectives:
1. To characterize sweetpotato farmers in C.Ug
2. To determine the value farmers are willing to
pay for virus- free sweetpotato vines
3. To determine factors affecting famers’ WTP
for virus- free sweetpotato vines
4. To estimate the market potential for Virus –
free sweetpotato vines
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 Study done in Mpigi and Wakiso district
 200 farmers sampled and questionnaire used
 Contingency valuation methods used to
estimate price
Data Analysis
Objective 1: Farmers categorized into 2 groups
 Descriptive statistics, t tests and chi square
tests used to test significance
 Objective 2: Means estimated and compared
using t test
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Objective 3: Tobit model specified as:
Ai* = b 0 + b1 X1 + b 2 X 2 + b 3 X 3 + - - - - - - - - - - - - b10 X10 + e
Ai* - latent variable indexing WTP.
βo – Intercept
β1…………… β10 are parameters to be estimated
X1…………X10 are the various independent variable
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Description of independent variables used in Analysing Factors Affecting
Farmers’ WTP for Virus Sweetpotato Vines
-free
Variable Description Unit of measurement
X1 Age of the farmer Number of years
X2 Education level of household head
o Number of years spent in
school
Membership in Association 0 = no, 1 = yes
x3
Access to extension services Number of times per year
x4
Access to credit services 0 = no, 1 = yes
x5
Farmer sells sweetpotato 0 = no, 1 = yes
x6
Access to quality vines 0 = no, 1 = yes
x7
X8 Revenue from sweetpotato Uganda shillings
X9 Market access Distance (km)
X10 Total area under sweetpotato production acres
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 Objective 4:
Where: MP = is the market potential
N= Number of farmers willing to buy virus-free
vines.
P= Mean WTP
Q=Number of planting seasons per year
A= Average number of bags required by each
farmer
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Socio- Unit of Farmers Farmers P
economic measure not willing willing to value
characteristics to pay pay more
more than than
8000/= 8000/=
Age Years 39.29 45.12 0.005
(13.40) (14.12
Education Number 6.78 6.68 0.849
level of years (3.82) (3.41)
spent in
school
Land access Acres 4.77 5.54 0.321
(4.51) (4.94)
Family size People 5.92 5.69 0.636
(3.31) (3.41)
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Socio- Unit of Percentage Percentage P value
economic measure numbers of number of
characteristics farmers not farmers
willing to willing to
pay more pay more
than than
8000/= 8000/=
Gender Male 51.56 48.44 0.863
Female 52.89 47.44
Experiencing Yes 50.91 49.09 0.233
SPVD No 65.00 35.00
Access to Yes 51.55 48.45 0.624
good quality No 52.87 47.13
vines
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T-test Results Comparing mean prices
Variable Mean Confidence P Value
(UShs) interval (UShs)
Price for virus- 8459 7,844 -9,074 0.0000
free vines (4239)
Price for 2611 800 - 4421
farmer-saved (1991)
vines
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Results Obj.3
Dependent variable Units of measure Coefficient t-statistic Pvalue
Price of Virus Vines
-free Uganda Shillings
Constant 6958.685 2.48 0.014
Age of the farmer Years 40.740 1.72* 0.088
Education of the farmer years in school 15.094 0.16 0.871
Membership in association (0 = no, 1= yes) -206.814 -0.26 0.797
Access to extension services No. of times/yr -98.60 -0.46 0.644
Access to credit services (1= no, 2= yes) 792.045 1.14 0.255
Farmer sells sweetpotato (1= no, 2= yes) 1751.372 2.09** 0.038
Access to quality vines (1= no, 2= yes) 709.1317 1.12 0.262
Revenue from sweetpotato Uganda Shillings 0.0037 2.34** 0.021
Market access Distance (km) -169.5612 -3.30*** 0.001
Total area under sweetpotato (Acres) 654.739 1.91* 0.058
No. Observations=180
Prob>chi2 0.012
=
2
Pseudo R 0.0067
=
Loglikelihood-1672.1928
=
Note: 1. (*) is significance at 10%, (**) Significance at 5%, (***) significance at 1%.
Observation Summary: -censored observations at WTP<=1000;
4 left
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Detail Amount Units
Number of possible 532,543 Farmers
buyers
Mean WTP Price 8400 Uganda Shillings
Average annual 2 planting seasons
purchasing rate
Average purchasing 4 bags per season
quantity
Market potential 35.8 Billion Uganda Shillings
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 There is no major variation between the two
categories of farmer. Only variation is age, implying
more experience and better appreciation of effects
of SPVD
 Farmers were willing to pay for quality vines
 Commercial oriented sweetpotato farmers
expressed a higher WTP than subsistence
sweetpotato farmers
 There is a big market potential for virus-free
sweetpotato vines
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Thank you for listening!
Cassava Potato and Sweetpotato
Bioinnovate Consortium - MAK
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