Willingness to pay for improved vision in Mozambique

Figures & data

Table 1. Demographic characteristics of study participants.

Category	Characteristic	Frequency	%
Location	Urban Semi urban Rural	381 351 405	33.5 30.9 35.6
Gender	Male Female	593 544	52.2 47.8
Literacy	Literate Illiterate	701 436	61.7 38.3
Level of schooling	No secondary school Secondary school Degree	971 135 31	85.4 11.9 2.7
Employment status	Employed Self employed Unemployed Retired	172 767 170 28	15.1 67.5 15.0 2.5
Personal income per month	0 – <2,000 Meticals >2,000 Meticals	883 254	77.7 22.3
Family income per month	0 – <2,000 Meticals >2,000 Meticals	767 370	67.5 32.5

Table 2. Profile of vision impairment among participants, classified according to measured VA.

Vision loss category	Definition by VA in the better eye ^a	Frequency	%
No VI Mild VI Moderate VI Severe VI Near VI	No VI <6/12 but ≥6/18 <6/18 but ≥6/60 <6/60 but ≥3/60 <6/12 but ≥3/60 for near, but ≥6/12 for distance	803 40 80 18 196	70.6 3.5 7 1.6 17.2

^a Snellen VA or the equivalent calculated from published LogMAR values.

Figure 1. WTP variance between the two methodologies.

Table 3. Stated choice and final bid willingness to pay values according to demographic characteristics.

Characteristic	Variable	Stated WTP Mean (SD)	Final bid WTP Mean (SD)
Sex	Male Female Cohen’s D (effect size)	440.69 (594.843) 332.50 (605.414) 0.180	543.68 (703.448) 389.47 (613.762) 0.234
Spectacle ownership	Has spectacles No spectacles Cohen’s D (effect size)	670.00 (979.962) 365.64 (553.854) 0.382	779.89 (1069.218) 444.21 (615.088) 0.385
Personal income	<2,000 Meticals/month >2,000 Meticals/month Cohen’s D (effect size)	293.33 (457.893) 721.26 (868.345) −0.616	346.31 (478.302) 899.53 (978.208) −0.719
Family income	<2,000 Meticals/month >2,000 Meticals/month Cohen’s D (effect size)	266.40 (437.965) 642.92 (788.644) −0.590	307.72 (434.976) 806.08 (897.634) −0.707
Location	Urban Semi urban Rural	522.78 (763.712) 392.09 (578.835) 260.25 (383.368)	612.61 (772.412) 488.28 (639.124) 319.70 (539.399)
Employment status	Employed Self employed Unemployed Retired	819.80 (1075.468) 291.70 (394.532) 388.71 (547.439) 406.61 (428.723)	961.45 (1044.054) 354.15 (493.166) 497.88 (662.902) 451.07 (442.981)
Education	No secondary Secondary school Degree	311.29 (426.181) 660.70 (856.344) 1637.10 (1562.582)	381.40 (500.905) 773.19 (872.630) 1920.97 (1565.555)
VI category	No VI Mild VI Moderate VI Severe VI Near VI	405.85 (607.300) 481.50 (536.874) 297.75 (456.962) 288.06 (433.716) 347.17 (653.710)	491.33 (666.268) 578.50 (760.356) 391.50 (528.738) 255.00 (358.563) 411.63 (710.998)
VI status (actual or perceived)	Actual & perceived Actual & not perceived Perceived but not actual No actual or perceived	355.79 (601.345) 222.89 (277.055) 454.90 (624.798) 368.33 (591.517)	429.21 (680.459) 238.42 (226.747) 547.64 (669.924) 448.26 (660.960)

Table 4. Response variance from mean WTP values.

Methodology	Below the mean	Equal the mean	Above the mean
Stated choice	762 (67%)	0 (0%)	375 (33%)
Bidding game	760 (66.7%)	3 (0.3%)	374 (33%)

Table 5. Scope analysis to investigate if, when additional benefits were offered, WTP values increased (positive response) or not (negative response).

Scope response	Stated WTP Mean (SD)	Final bid WTP Mean (SD)
Positive response	417.05 (630.236)	504.11 (661.965)
Negative response	298.61 (491.397)	360.04 (669.267)

Figure 2. Association between starting bids and final bids.

Table 6. Final bid WTP values according to starting bid.

Start bid (Meticals)	Mean (SD)
500 1,000 1,500 2,000	503.46 (698.697) 457.09 (571.655) 464.13 (816.696) 453.09 (527.825)

Table 7. Multivariate analysis to assess relationships between WTP and several variables simultaneously.

	Stated WTP			WTP Final Bid
	Coef.	t	P-val	Coef.	t	P-val
Age*	−3.408 †	−2.29	0.022	−3.434†	−2.17	0.030
Female	−75.502 †	−2.23	0.026	−135.60†	−3.77	0.000
Level of school ^a
Secondary School	117.775†	2.19	0.028	93.747	1.64	0.100
Degree	746.311†	6.67	0.000	822.858†	6.92	0.000
Employment status ^b
Self Employed	−181.67†	−3.4	0.001	−187.37†	−3.31	0.001
Unemployed	−132.067	−1.96	0.050	−100.464	−1.4	0.161
Retired	−116.906	−1.02	0.310	−147.964	−1.21	0.226
Personal Income *	16.991	0.64	0.521	−15.429	−0.55	0.583
Household Income *	87.326†	3.95	0.000	156.150†	6.66	0.000
Do not have glasses	−29.914	−0.46	0.645	2.647	0.04	0.969
Location ^c
Semi Urban	−30.448	−0.75	0.454	−2.721	−0.06	0.950
Rural	−99.684†	−2.47	0.014	−91.038†	−2.12	0.034
VI Category ^d
Mild VI	31.582	0.34	0.737	29.921	0.3	0.765
Moderate VI	20.214	0.26	0.792	48.104	0.59	0.554
Severe VI	8.094	0.06	0.953	−88.776	−0.61	0.540
Near VI	17.733	0.3	0.762	13.475	0.22	0.828
VI Actual or Perceived ^e
Actual but not perceived VI	−122.335	−0.95	0.341	−164.366	−1.2	0.229
Perceived but not actual VI	9.618	0.24	0.813	8.967	0.21	0.836
Constant	656.765†	6.44	0.000	693.372†	6.4	0.000
Model Diagnostics
F(18,1111)	20.5300			27.2400
Prob > F	0.0000			0.0000
R^2	0.2496			0.3062
Adjusted R^2	0.2375			0.2950

* Age, personal income and household income were continuous variables. All others were categorical.

^† significant at 5 per cent level.

Reference categories: ^a No secondary; ^b Employed; ^c Urban; ^d No VI; ^e Actual and perceived VI.