Influences of various pricing points: an experimental study of plastic bags in Johannesburg, South Africa

Figures & data

Table 1. Sample of contingent behaviour chart for plastic bag price-change questions posed to respondents.

Actual		Hypothetical Increases
Price	Number of Bags	Price	Number of Bags	Price	Number of Bags	Price	Number of Bags	Price	Number of Bags
$0.03		$0.06		$0.13		$0.25		$0.50

Table 2. Stated purchasing behaviour by price level.

Price	Buy (%) *	Mean Number of Bags Per Month*
$0.03	63.9	14.96
$0.06	26.5	6.21
$0.13	7.3	1.73
$0.25	1.6	0.39
$0.50	0.7	0.17

^{* Buy percentages were based on a total sample of 421 respondents.}

Table 3. A selection of descriptive statistics of the 421 shoppers interviewed.

Variable	Mean	Std Deviation	Min	Max
Number of bags purchased (at actual price)	14.96	14.49	0	140
Know current bag price	0.7	0.46	0	1
Aware of bag prices	0.39	0.49	0	1
Reuse of bags	0.88	0.33	0	1
Household Income $	8 033	9 309	392	39 154
Age	39.29	14.53	18	95
Household size	3.7	2.02	0	20
Education years	13.07	1.91	0	18
Low Education Dummy	0.4	0.49	0	1
Gender	0.51	0.5	0	1
Married dummy	0.47	0.5	0	1

Table 4. Tobit with Bootstrap Std. Err. for modelling plastic bag use.

Variable	RE Tobit (Linear Linear)		Tobit (Linear Linear)
Equation	ME1	ME2	ME3	ME4
Price	−11.04***(0.989)	−11.045***(0.967)	−1.77***(0.078)	−10.498***(1.010)
Income		0.00002*** (3.09e-06)		0.00002*** (4.45e-06)
Awareness		−0.685 (0.712)		−0.997***(0.927)
Reuse		−7.70***(1.382)		−8.225***(1.954)
Age		−0.053*** (0.026)		−0.045 (0.036)
Household Size		0.65***(0.162)		0.702***(0.199)
Education (Years)		−0.46* (0.262)		−0.512**(0.380)
Employment Dummy		−1.68** (0.852)		−1.844(1.190)
Female Dummy		−0.108 (0.690)		−0.057 (0.919)
Constant	13.2***(0.942)	25.3***(4.197)	9.08***(0.372)	25.3***(6.073)
Sigma_u	9.64***(0.791)	8.88***(0.727)
Sigma_e	11.9***(0.779)	11.9***(0.733)
Var (e.Quantity)			80.3***	228.1***
Log likelihood	−3585.4	−3565.91	−3688.96	−3648.06
Chi-squared	124.7	176.8	510.4	145.3
Bayesian Information Criteria	7201.4	7223.5	15,011.7	7380.1
Observations	2075	2075	2075	2075

Standard errors in parentheses. M1= RE Tobit Reduced Marginal Effects M2= RE Tobit Marginal Effects M3= Pooled Tobit Reduced Marginal Effects M4= Pooled Tobit Marginal Effects.*p<0.10, **p<0.05, ***p<0.01.

Table 5. Plastic bag price elasticities.

Price US$/PB	Random Effects Tobit Model (Linear-Linear)
0.03	−0.139***[0.139]
0.06	−0.272***[0.022]
0.13	−0.501***[0.037]
0.25	−0.795***[0.043]
0.50	−0.997***[0.025]