metadata: authors: 0: author: Mekonnen,Alemu
1: author: Beyene,Abebe D.
2: author: Bluffstone,Randall Ames
3: author: Dissanayake,Sahan
4: author: Gebreegziabher,Zenebe
5: author: LaFave,Daniel
6: author: Martinsson,Peter
7: author: Toman,Michael A.
count: Ethiopia
docna: 0: docna: Improved Biomass Cookstove Use in the Longer
            Run : Results from a Field Experiment in Rural Ethiopia
docty: Policy Research Working Paper
subtopic: Energy and Environment,Energy Demand,Energy and Mining,Health Care Services Industry,Tobacco Use and Control,Public Health Promotion,Disease Control & Prevention,Hydrology,Pollution Management & Control,Air Quality & Clean Air,Brown Issues and Health
teratopic: Energy,Industry,Health, Nutrition and Population,Water Resources,Environment
abstracts: cdata!: This paper reports on
            electronically-monitored improved use of the
            "Mirt" biomass stove in Ethiopia over a relatively
            long period of three-and-a-half years, using stove use data
            collected at five points in time. The results show that 62
            percent of the households surveyed still retained their
            stoves after more than three years, which is a low level of
            abandonment, as the lifetime of the Mirt stove is
            approximately five years. Dis-adoption of the stove is not
            correlated with any of three monetary incentives provided at
            the time of distribution. With and without adjusting for
            dis-adoption, no longer-run differences in stove retention
            are found across treatments. Among those who retained their
            stoves, average regular stove use increased over time, but
            generally it is statistically the same toward the end of the
            first year. Thus, despite the relatively long timeframe, no
            decline is observed in regular usage. Comparing the
            persistence of the treatment effects, the paper finds that,
            in the longer run, subsidizing the cost most effectively
            promotes increased regular use over time.
geo_reg_key: 517191
repnme: repnme: Improved Biomass Cookstove Use in the
            Longer Run : Results from a Field Experiment in Rural Ethiopia
display_title: Improved Biomass Cookstove Use in
            the Longer Run : Results from a Field Experiment in Rural Ethiopia
listing_relative_url: /research/2020/06/32106223/improved-biomass-cookstove-use-longer-run-results-field-experiment-rural-ethiopia
topicv3: Water m1326522 137,Energy and Extractives m1326595 507,Tobacco Use and Control m1326794 1439,Air Pollution m1327122 1791,Health m1504661 3480
publishtoextweb_dt: 2020-06-08T00:00:00Z
historic_topic: Energy,Industry,Health, Nutrition and Population,Water Resources,Environment
origu: DEC-Sustainability & Infrastruct (DECSI)
no_of_pages: 38
author_keys: 0: author_key: 633741
1: author_key: 166060
model_extractions: Policy Research Working Paper 9272 Improved Biomass Cookstove Use in the Longer Run Results from a Field Experiment in Rural Ethiopia _Alemu Mekonnen Abebe D. Beyene Randall Bluffstone Sahan Dissanayake Zenebe Gebreegziabher Daniel LaFave Peter Martinsson Michael A. Toman_ Development Economics Development Research Group June 2020
Policy Research Working Paper 9272

# **Abstract**

This paper reports on electronically-monitored improved use of the “Mirt” biomass stove in Ethiopia over a relatively long period of three-and-a-half years, using stove use data collected at five points in time. The results show that 62 percent of the households surveyed still retained their stoves after more than three years, which is a low level of abandonment, as the lifetime of the Mirt stove is approximately five years. Dis-adoption of the stove is not correlated with any of three monetary incentives provided at the time of distribution. With and without adjusting for dis-adoption, no longer-run differences in stove retention are found across treatments. Among those who retained their stoves, average regular stove use increased over time, but generally it is statistically the same toward the end of the first year. Thus, despite the relatively long timeframe, no decline is observed in regular usage. Comparing the persistence of the treatment effects, the paper finds that, in the longer run, subsidizing the cost most effectively promotes increased regular use over time.

This paper is a product of the Development Research Group, Development Economics. It is part of a larger effort by the World Bank to provide open access to its research and make a contribution to development policy discussions around the world. Policy Research Working Papers are also posted on the Web at http://www.worldbank.org/prwp. The authors may be contacted at mtoman@worldbank.org.

_The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent._ Produced by the Research Support Team
# **Improved Biomass Cookstove Use in the Longer Run: Results from a Field Experiment in Rural Ethiopia**

Alemu Mekonnen<sup>*</sup> , Abebe D. Beyene, Randall Bluffstone, Sahan Dissanayake, Zenebe Gebreegziabher, Daniel LaFave, Peter Martinsson, Michael A. Toman Key Words: Household Air Pollution, Biomass, Ethiopia, Improved Stove JEL Codes: Q55, Q23, Q42

> * Corresponding author Mekonnen: Addis Ababa University, Addis Ababa, Ethiopia; Beyene: Policy Studies Institute, Addis Ababa, Ethiopia; Bluffstone, Portland State University, Portland, OR, USA Dissanayake: Portland State University, Portland, OR, USA; Gebreegziabher, Mekelle University, Mekelle, Ethiopia; LaFave: Colby College, Waterville, ME, USA; Peter Martinsson, Gothenburg University, Gothenburg, Sweden; Toman, World Bank Development Research Group, Washington DC, USA.
# **Improved Biomass Cookstove Use in the Longer Run: Results from a Field Experiment in Rural Ethiopia**<sup>**1**</sup>

## **1. Introduction**

Despite enormous progress in other areas of human development, as of the second decade of the 21<sup>st</sup> century C.E., approximately two in five people still cook with solid fuels (e.g. biomass, coal) burned in their main homes or nearby buildings (Grieshop et al., 2011; IEA, 2012; Jeuland et al., 2015b; Jeuland and Pattanayak, 2012). This reliance, particularly on biomass fuels like fuelwood, agricultural wastes and animal dung, is primarily concentrated in low-income developing countries (Jeuland et al., 2015a), contributing to indoor and outdoor air pollution, forest degradation and climate change (Bailis et al., 2015). Though across the world the percentage of people depending on biomass fuels has declined dramatically in the past 20 years and will continue to decline, the absolute number of people who will continue to depend on biomass fuels is expected to remain the same through 2030 and decline only slightly by 2040 (IEA 2006; 2014). This is likely to also be true in Ethiopia, which is the focus of this paper. Ethiopia depends on biomass for over 90% of its energy (Geremew et al., 2014), though reliance on commercial fuels is expected to increase in the coming decades (Mondal et al., 2018).

To ease the transition to modern fuels like LPG, electricity and biogas, improved biomass cookstoves (ICS) have been introduced around the world as an intermediate step. These stoves seek to provide efficiencies by cooking meals with less fuel, resulting in less fuelwood consumption (Mondal et al., 2018) and potentially offer improved performance in other ways compared with traditional technologies (Gebreegziabher, 2018). These stoves are typically not sophisticated, are

> 1 The authors gratefully acknowledge helpful comments on the paper from participants at the 2019 SETI conference in Santiago Chile, and financial support from the World Bank’s Knowledge for Change Trust Fund.  Responsibility for the content of the paper is the authors’ alone.

2
often cheap (e.g. Hanna et al., 2016) and generally require minor changes in cooking habits (Jeuland and Pattanayak, 2012).

Many ICS were introduced in the 1980s and generally accepted into peoples’ homes, but often it was found that cooks did not regularly use these stoves (e.g., Gil 1987 and Barnes et al. 1993). It soon came to be recognized that ICS adoption really has two parts. The first is acceptance to try stoves, which implies distribution to households. The second and more ambitious aspect of adoption is regular use, which has come to be seen as the main litmus test of true adoption (Beyene, et al., 2015; Bensch and Peters, 2015; Hanna et al. 2016; Johnson et al. 2009). For this reason, in this paper we focus on adoption measured as regular use.

We examine adoption of the Mirt ICS, which has been promoted in Ethiopia since 1998, and is used primarily to cook injera. Mirt has been estimated to use 50% less wood in laboratory tests (GIZ, 2011), 40% to 50% based on surveys (Megen Power, 2008; Dresen et al., 2014) and 20% to 30% under field-based controlled cooking tests (Gebreegziabher et al., 2018). Injera is a type of pancake that is widely eaten in Ethiopia and requires hot, even energy delivery to be properly baked. For this reason, injera is baked on a clay pan called a mitad, using very high heat. The average household uses about 20 kg of fuelwood per week to make injera and injera baking is estimated to use about half of the primary energy of the country (Bizzari, 2010; Tesfay, 2014; DFID, undated). Very few rural households in Ethiopia use ICS (Mondal et al., 2018), with most households relying on three-stone tripods that waste approximately 90% of the energy input (DFID, undated; Alem et al., 2013).

We extend our previous work on this topic, which examined use of Mirt over a period of about a year (Beyene et al. 2015) for three monetary treatments which were randomly applied at baseline. Injera is not cooked every day, but regular baking would take place at least twice per week 3
in areas like our study regions, which lack refrigeration. Regular usage of the Mirt injera stove therefore means using it at least twice per week (Bizzarri, 2010; Tesfay, 2014; DFID, undated).

The monetary treatments applied at baseline included providing the stoves free of charge, at a subsidized cost and with an incentive to regularly use the Mirt ICS during the first monitoring period after distribution. In our paper, which examined behaviors that occurred within the first year, we found that households in general regularly used the Mirt stove. We also found that average usage – and average regular usage – increased over time, with free distribution promoting both sustained high levels of regular use and increases in average usage over time. Paying for Mirt was found to only promote increased usage, mainly because average use in the beginning was very low compared to other treatments. We therefore concluded after one year of evidence, that Mirt is appropriate for users and from a regular usage perspective free distribution is the preferred treatment (Beyene et al., 2015; Bluffstone et al., 2018).

In this paper, we test whether these results hold up or change in the very long run, which we define as approximately three-and-a-half years after initial distribution of the Mirt stove. This period is about 70% through the estimated lifespan of Mirt, which allows us to examine common ICS program outcomes that were not observed during the first year. These include dis-adoption and abandonment due to breakage, poor fit, etc., which are common to ICS programs (e.g. see Hanna et al., 2016), but were not observed during our shorter-run analysis. It also allows us to see if use behavior, and especially reaction to the initial treatments applied in 2013, has changed during the approximately 2.5 years since the Mirt stoves were last monitored.

We find that 62% of households continue to have their Mirt stoves after about 3.5 years and most of those who no longer have them report they abandoned due to breakage. In our shorter-run analysis no stoves were abandoned. Among those who have retained their stoves, Mirt stove use is 4
high and in line with regular use on average. If anything, usage frequency has increased over time, but the changes are minor; we conclude that in the long run the Mirt stove continues to on average be regularly used.

We analyze the long-run effects of our three monetary incentives with and without adjusting for abandonment. We find that usage intensity in after 3.5 years after the introduction is not driven by the monetary incentives given at the time of the introduction. In contrast to our shorter-run analysis, while free distribution does no worse at promoting persistent long-run regular usage, it is not more effective than the other treatments.

Our study contributes to the limited literature on the intensive and extensive margin of adoption of improved stoves in the very long run with Bensch and Peters (2015) and Hanna et al. (2016) being the major exceptions. Our findings are in line with those of Bensch and Peters (2015) in rural Senegal who found that ICS take up was high. One possible explanation for this is that the stove is simple and easy to use since it only consists of a couple of concrete parts. In our previous work, we found that maintenance of the Mirt stove is low and user satisfaction very high (Gebreegziabher et al., 2018). On the other hand, Hanna et al. (2016) found that adoption and performance of the stove they studied declined over the four years examined, mainly due to high maintenance cost of the stove.

The next section discusses the key literature that is germane to our question and our conceptual framework. Section 3 discusses the methods and Section 4 presents results. Section 5 discusses the findings and Section 6 presents our conclusions.

5
# **2. Literature review and conceptual framework**

# _2.1 Literature review_

In this section, we briefly review previous literature on long-run adoption of new technologies with regard to monetary treatments. Of the two parts of ICS adoption – distribution and regular use – the second part is both more ambitious as well as important. Typically, financial incentives such as subsidies and rewards have been used to promote distribution, but very often concerns are raised that promoting distribution by offering stoves free or at low cost may waste resources and even reduce usage. This idea is summarized in the adage “Free goods are worth what you pay for them” (Economist, 2008), but recent research, which has focused on infectious disease prevention, appears to be calling this into question since initial trials might pave the way for habit formation. To date, however, clear evidence does not exist for ICS and the literature has almost exclusively focused on explicitly health-related technologies; our paper provides evidence that lessons from this important literature may also apply to ICS.

Financial incentives, such as subsidies and monetary rewards, are used to promote technology adoption. At least in the health realm, such treatments have also been rigorously evaluated (e.g., Cohen and Dupas, 2010; Dupas, 2014; Ashraf et al., 2010; Chassang et al., 2012). Other instruments to induce behavioral changes and enhance adoption in diverse spheres of life, including energy conservation, smoking cessation and adherence to medication, include social comparisons (e.g., Schultz et al. 2007; Nolan et al. 2008), and providing nudges (Allcott and Rogers, 2012 and 2014). Abrahamse et al. (2005) provide a useful review of the literature on behavioral interventions centered around energy conservation. They conclude that information does not necessarily result in behavioral changes or energy savings. They also find that payments for adoption of energy efficiency technology encourage short-run adoption, but effects dissipate in the long-run.

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Free or low-cost distribution of technologies obviously reduces liquidity constraints, potentially promoting adoption (e.g., Cohen and Dupas, 2010; Bensch et al., 2015), but these incentives can also have efficiency effects. Subsidies may reduce screening, implying that technologies go to those who do not value them and will not use them (e.g., Ashraf et al., 2010; Chassang et al., 2012). Free distribution may also mute psychological sunk cost effects that promote use. There is a growing literature on how monetary dimensions affect adoption and use of goods and services, such as mosquito nets (Dupas, 2014), exercising at gyms (Charness and Gneezy, 2009) and water treatment products (Ashraf et al., 2010). In general, little evidence seems to exist that psychological sunk costs promote use (Ashraf et al., 2010; Cohen and Dupas, 2010) or that users in the long-run anchor on subsidized prices (Dupas, 2014; Bensch and Peters, 2017).

Perhaps the most significant work has been on insecticide-treated bed nets in Sub-Saharan Africa. The WHO, on behalf of the Global Fund to Fight AIDS, Malaria and Tuberculosis, analyzed free distribution of bed nets versus charging nominal prices. They find that in general free distribution is most effective (Economist, 2008). Dupas (2014) also shows that a one-time subsidy can boost the purchase of mosquito-repellent bed nets and that those who received the bed nets under concessionary terms do not anchor their valuations on these subsidized prices. Cohen and Dupas (2010) do not find a significant difference in the use of bed nets between households who paid compared with those who received their bed nets for free. In a field experiment in Zambia, Ashraf et al. (2010) investigate the intensity with which chlorine to treat drinking water is used. They find that higher prices of chlorine increase the average probability that people use it by screening out low-value users. They find little evidence, however, that high sunk costs promote use.

A second potential treatment is payments for performance. Cahill and Perera (2011) review the effectiveness of incentives for smoking cessation. They argue that, though there seems to be 7
some evidence that incentives work in the short-run, generally their effects dissipate and there is no clear evidence that initial behavior changes translate into routine practice. Kane et al. (2004) decompose behavioral changes into 'simple' (single actions at a point in time), such as adherence to medication, and 'complex' (requiring effort over a sustained period of time) like smoking cessation and weight loss to reduce obesity. According to Aveyard and Bauld (2011) and Giuffrida and Torgerson (1997), incentives are effective for simple, but not for complex, behavior change. They argue that complex behavior change requires multiple strategies. Moreover, the effectiveness of interventions often declines when the incentive is withdrawn (Paul-Ebhohimhen and Avenell 2007).

# _2.2 Conceptual framework_

To understand improved biomass stove use decisions and generate testable hypotheses, we utilize the analytical model presented in Bluffstone et al. (2018), which modified the one-period analytical model of Jeuland et al. (2015a). The key findings of the analytical model are given below and short-run results from Bluffstone et al. (2018), which refined the initial work in Beyene et al. (2015), confirm these priors. Our current paper examines if these results are in any way affected by moving to the long run. We re-examine two hypotheses considered in previous work using data that cover a longer period:

- i) Positive stove prices do not affect stove usage decisions unless there is a screening effect at the time of sale;

- ii) Pay-for-performance schemes have higher usage rates compared with the other two monetary treatments during the incentivized period.  Effects beyond the performance period are ambiguous.

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# 3. **Field experiment**

# _3.1. Design_

The field experiment involved distributing the Mirt stove under different terms to a sample of households in 2013. In our study area and throughout much of Ethiopia, households with no refrigeration typically bake injera at least twice per week (Bizzarri, 2010; Tesfay, 2014; DFID, undated). This is the definition of regular usage.

We identify cooking events by measuring the surface temperature of the Mirt stoves using electronic Stove Use Monitors (SUMs).<sup>2</sup> The SUMs we used are approximately the size of a watch battery (see Figure 1). We set the SUM device to record surface temperature every 10 minutes and the memory can record for approximately 60 days and can tolerate temperatures up to 120 degrees Celsius. Temperature, time and date data are then downloaded after the monitoring period is completed. Respondents were informed that the purpose of the SUM device was to record the surface temperature of the stove and that enumerators would come back periodically to download the data and reinstall the SUM devices.

We have three levels of monetary incentives: (i) users receive the stove for free; (ii) users pay 25 birr for the Mirt stove (about 13% of the real cost),<sup>3</sup> and (iii) users pay nothing for their stoves and receive a 50 birr<sup>4</sup> incentive payment if the stove use monitors (SUM) that were affixed to all

> 2 The Mirt stoves are monitored over five periods of up to about 8 weeks per period over approximately three-and-a-half years. A subset of 108 households participated in three controlled cooking tests that are not part of this study but are discussed in Gebreegziabher et al. (2018).  In our regression models we control for participation in this activity.

> 3 This is a typical subsidized cost level if stoves are not provided free as in Rosa et al. (2014).  For example, in Ethiopia, World Food Program (undated) reports offering an 80% subsidy.  Though the technology analyzed is LPG stoves rather than ICS, Bailis (2018) also reported an 80% subsidy in their RCT in India.

4The exchange rate in June 2013 when the Mirt stoves were distributed was approximately ETB 19/$US and the daily unskilled wage rate was approximately ETB 40. Half the sample was randomized into village level groups that received one-time group training. These groups were made up of households in the same village sites who received the Mirt stove. These groups were found to have no effect on usage and are treated as a control in all models, but not analyzed.

9
stoves indicated that the Mirt stoves were used at least twice per week (i.e. regularly used) during the first monitoring period.

Figure 1. Stove Use Monitors (SUMs) Source: Abebe D. Beyene Using signal processing and analysis (O’Haver 1997), we measured frequency of stove use for a monitoring period by simply counting the number of times the stove surface temperature exceeded a critical value. The average stove use in a period is calculated as the number of cooking events/total days temperature was measured. Because injera is not baked daily, we express this value per week and define regular use of the stove as an average use of at least twice per week.

Based on readings from the SUMs, we identify a cooking event as having taken place if the recorded temperature exceeded 40 degrees Celsius. We chose 40 degrees as our cutoff, because it is about 14% greater than the maximum in-home ambient temperature measured using thermometers, which was 35 degrees Celsius. We therefore reduce the possibility of counting normal temperature variations as cooking events by using the 40-degree Celsius cutoff. We also conduct robustness checks with 45 and 60-degree Celsius cutoff points and find that the results do not change (see Appendix B).

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The three-stone tripod is the traditional injera baking technology in rural Ethiopia and in our study sites. It is, unfortunately, difficult to reliably monitor three-stone tripod cooking using SUMs, because the stones are often moved, and fires are less controlled than with an enclosed stove. Inference about exclusive use of the stove and potential rebound effects is, therefore, imperfect. Considering that households will in any case need to use three-stone tripods to cook most noninjera foods and we are analyzing frequency of stove use and not fuel savings, injera cooking rebound effects would be difficult to detect and not terribly relevant for this paper. There is a possibility that because of reduced fuelwood consumption per meal, cooks may cook more or pay less attention to fuelwood use; both these results would be scale effects and as they are equally probable for all stoves, neither would generate biased estimates across treatments.<sup>5</sup>

# _3.2. Sampling and fieldwork_

Our sampling frame is based on a random sample of 110 villages in local jurisdictions called kebeles _,_<sup>6</sup> from a 2012 study by the Ethiopian Development Research Institute (EDRI). We eliminate 29 of the 110 sites, because they were part of our pilot survey, _injera_ is not typically baked in these villages or the normal three-stone tripod technology is not used.

We then selected 36 villages using stratified proportional random sampling from the 81 villages that were left. Stratification was by regional state (Amhara, Oromia and Southern Nations, Nationalities and Peoples), with forest area used as the state weight. Forest area is used, because most fuelwood comes from forests and it also proxies well for total regional state population and land area. In total, 20% of villages are from Amhara, 50% from Oromia and 30% from SNNP regional states.

> 5 The Mirt injera stove has a 50 cm burner, which cannot accommodate normal pots.  The way the stove is designed therefore makes it virtually impossible to shift to other uses (a potential rebound effect).

> 6 _Kebele_ translates as peasant association and is made up of several villages.  It is the smallest official jurisdiction in Ethiopia. We have only one village per _kebele_ and therefore we use village and _kebele_ interchangeably.

11
A total of 504 households were randomly selected from the 36 village clusters (14 households in each site), with 10 households receiving the Mirt stove in each village (total of 360 households). The remaining 144 households (4 from each site) did not receive the stove and serve as controls to measure fuelwood usage. As we only analyze Mirt stove use in this paper, however, we do not use these controls.

Participants of the survey were informed about the nature of the survey and experiment and formal oral consent was received from all respondents. Full information was provided to respondents on stove features, the use of the SUMs, details about the treatments applied to them and that stove use is not required to receive a stove. Respondents were told that the stove is expected to save wood and were encouraged to use them. While the strategy to address refusals was to replace refusing households by randomly choosing from remaining households in each site, there were no refusals and no attrition until the final data collection period.

The baseline survey conducted in 2013 included household characteristics and socioeconomic variables. In 2016, when the final monitoring period occurred, a second survey was also conducted. This survey updated baseline household characteristics, but particularly focused on kitchen characteristics and use/disuse and abandonment of the Mirt stove. Field workers were experienced and were trained directly by investigators, with approximately four enumerators working under each of the five field supervisors. All of the supervisors and many of the enumerators who conducted the follow-up field work in 2016 also participated in the baseline research conducted in 2013.

In addition to installing the stoves in the injera baking area in the first period of the study, the fieldworkers installed the SUMs on the stove using heat-resistant tape and initiated them in each of the five periods the study was conducted. The five monitoring periods were: June-August 2013 12
(period 1); August-October 2013 (period 2); March-May 2014 (period 3); May-July 2014 (period 4) and November – December 2016 (period 5).

Randomization in the selection of recipients of the Mirt stove within each village is at the household level. Randomization of the price and network treatments is at the village level to ensure that all those in a village received their Mirt stoves on the same terms.<sup>7</sup> Households in Ethiopian villages are also likely to know the terms under which their neighbors received Mirt. Allocation of stoves using different treatments within a village in our study would have likely been perceived as unfair, potentially biasing usage intensity. This reflects implementation of improved stove programs at scale, where all individuals in villages would very typically receive stoves under the same conditions. In sum, therefore, treatments are assigned completely randomly across villages using the stratification procedure noted above and 10 households were randomly selected to receive Mirt stoves within each village.

# 4. **Results**

Our analysis starts with examination of those households who had abandoned their stoves by 2016 (about 3.5 years after the initial distribution of the stoves). This is then followed by analysis of long-run average usage, including effects of treatments on use of the stove at least twice per week, both accounting for and ignoring dis-adoption.

> 7 As noted in Beyene et al. (2015), using five key characteristics of our research sites across our six treatments, we tested whether randomization at the site level was successful. The variables used, which we believe are relevant to decisions on whether to use a new fuelwood saving technology, are number of households in the _kebele_ , proportion of households who are members of a forest user group, wealth variance in forest user group, percentage of forest biomass change over the previous five years and distance to market. As noted in Beyene et al. (2015), we find that randomization is successful, with none of the community variables significant at 5% level using Kruskal-Wallis tests.

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_4.1. Dis-adoption of stoves as of 2016_ At the end of 2016 (about three-and-a-half years after the first survey period), we conducted a visual inspection and survey to identify whether the stoves adopted in 2013 were still in place. Table 1 presents descriptive statistics on variables that are potentially correlated with continued presence of the stove. About 62% of those who received a stove still had it in place 3.5 years after initial distribution, which is high considering that these stoves were approaching the end of their approximately five-year lifespans.

About 83% of the 121 respondents who gave reasons for abandoning the stove said that the reason for abandoning the Mirt stove was breakage. Reasons given by the rest of the respondents included “I do not need it, because I do not bake injera” and “I have a better improved stove.” All the variables listed in Table 1 are from the 2016 data collection, except the last one on frequency of stove use per week in period 4, which is from period 4 of data collection using SUM devices. This variable is included, because it is the most recent indicator of stove usage intensity before the last period of data collection.

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Table 1. Descriptive Statistics on Variables Used to Analyze 2016 Stove Use

|Variable description|Mean|Std. Dev.|Min|Max|
|---|---|---|---|---|
|Stove still in use (1 if yes, 0 otherwise)|0.62|0.49|0|1|
|Incentive treatment|0.33|0.47|0|1|
|Pay treatment|0.35|0.48|0|1|
|Free treatment|0.29|0.46|0|1|
|Group training dummy (1 if yes, 0 otherwise)|0.49|0.50|0|1|
|Male headed household (1 if yes, 0 otherwise)|0.90|0.30|0|1|
|Stove is in main house (1 if yes, 0 otherwise)|0.23|0.42|0|1|
|Participated in CCT (1 if yes, 0 otherwise)|0.32|0.47|0|1|
|Corrugated roof (1 if yes, 0 otherwise)|0.15|0.35|0|1|
|Distance to all weather road in hours (two-ways)|0.87|1.16|0|6|
|Injera baking freq. since receiving stove (1 if once a<br>month or more, 0 otherwise)|0.98|0.30|0|1|
|Frequency of stove use per week in Round 4|2.05|2.38|0|18.61|

N=327 households.

Table 2 presents results of probit regressions to examine correlates of dis-adoption after 3.5 years since the introduction, where stove still in place is coded as 1 and 0 otherwise. The results in column 1 show that none of the treatments are correlated with retention of the stove when compared to the reference category of Free Treatment. The results are unaffected when other covariates are added, as shown in column 2. Households with stoves in the main house were less likely to have the stove in place as of 2016 (p<0.10), which may imply they are more easily broken in main living quarters. Households that participated in the controlled cooking test (CCT) were more likely to still be using the stove in 2016 (p<0.05). In our models with selection discussed below, the selection equations include all the variables in Table 1.

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Table 2. Probit regression of whether Mirt stove was in place in 2016

|Incentive treatment|0.050|0.043|
|---|---|---|
||(0.302)|(0.443)|
|Pay treatment|0.202|0.634|
||(0.312)|(0.409)|
|Network treatment (1 if yes, 0 otherwise)|-0.302|-0.242|
||(0.245)|(0.394)|
|Male headed household (1 if yes, 0 otherwise)||0.101<br>(0.228)|
|Stove is in main house (1 if yes, 0 otherwise)||-0.388<br>(0.215)*|
|Participated in CCT (1 if yes, 0 otherwise)||0.267<br>(0.134)**|
|Corrugated roof (1 if yes, 0 otherwise)||0.422<br>(0.282)|
|Distance to all weather road in hours (two-ways)||-0.143<br>(0.115)|
|Injera baking freq. since receiving stove (1 if once a month or<br>more, 0 otherwise)||0.807<br>(0.306)***|
|Frequency of stove use per week in Round 4||-0.015<br>(0.033)|
|Constant|0.349|0.255|
||(0.292)|(0.433)|
|N||327|

* _p_ <0.1; ** _p_ <0.05; *** _p_ <0.01.  Dependent variable is stove use, which is 1 if stove is still in use and 0 otherwise.

# _4.2. Stove use in the longer-run_

Our analysis of stove use in the very long run is presented in this sub-section. We look both at the intensive margin, which in this case is households that have not abandoned their Mirt stoves, and at the extensive margin using selection models to adjust for abandonment, mainly due to breakage. Our analysis focuses attention on period 5, with the objective to analyze very long-run effects. Controls are shown in Table 3. All variables are from our baseline survey conducted in 2013 and include a mix of socioeconomic and cooking metrics.

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Table 3. Descriptive statistics on variables used for analysis of long-run stove use

|**Variable**|**Mean**|**S. D.**|
|---|---|---|
|_Socio-economic_|||
|Age of respondent in years|42.134|13.172|
|Male|0.880|0.325|
|Education (Literate = 1, 0 otherwise)|0.383|0.487|
|Family size in adult equivalent|4.888|1.860|
|Number of livestock in tropical livestock units (TLU)|5.077|3.715|
|Randomly chosen to participate in controlled cooking<br>test (1 if yes, 0 otherwise)|0.300|0.459|
|Estimated coefficient of relative risk aversion<sup>8</sup>|3.815|1.214|
|_Cooking_|||
|Average number of_injera_baked at a time|19.721|10.303|
|Use the improved stove for any other purpose other than<br>baking (1 if yes, 0 otherwise)|0.333|0.472|
|Uses pure teff flour =1, 0 otherwise|0.156|0.363|
|The stove is installed inside the house (1 if yes, 0<br>otherwise)|0.360|0.481|

*The number of observations differs by variable, but the maximum is 360 households.

Table 4 and Figure 2 show frequency of Mirt stove use by period and treatment measured using the SUMs for those with stoves in place in 2016. The numbers represent average times the stove is used per week during the approximately 6-week monitoring periods. Average use per week ranges from 1.94 to 2.43 in period 5 depending on the treatment, all of which are in line with the normal injera preparation frequency of ≥ 2 times per week. In two out of three treatments, average use increased between periods 1 and 5 and the difference in average use in the treatment where use has declined is only about 0.2 times per week (about 10%). Without controls, average usage generally increased over the 3.5 years. Except for the Free Treatment households, though, there have been some declines in use since peaks in periods 3 and 4.<sup>9</sup>

> 8 See Vieider et al. (2014) for a discussion of the estimation method.

> 9 Comparing stove use in periods 1 and 5 for the 22 households with measurement in both periods, we find 54.6% used the stove at least twice per week in period 5, substantially more than the corresponding figure for period 1 (40.9%).

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<!-- Start of picture text --> ° 2.71 2.73<br>2.5 2.44 a) 42 g.43<br>2.08 22 2.28.2<br>1.96 1.94<br>2 1.81<br>1.58<br>1.5<br>1<br>0.5<br>(e)<br>Period 1 June- Period 2 (August Period 3 (March- Period 4(May— Period 5 (Nov.—<br>August 2013) —- October 2013) May 2014) July 2014) Dec. 2016)<br>mw 50 Birr use incentive (Incentive) m Paid 25 Birr (Pay) m Received stove for free (Free)<br><!-- End of picture text -->
degrees C, and 60 degrees C). We define use in this way to focus on true adoption in the sense that households use the Mirt stove in accord with normal injera baking frequency. In these models we ignore dis-adoption.

As robustness checks, we apply Heckman probit (Heckit) and Heckman selection models to analyze usage intensity after accounting for differences between those who still have their stoves in place and those who do not. Tables 5 and 6 do not include details on socioeconomic and cooking characteristics, but these are shown in Appendices A, B, and C respectively.

Table 5 presents random effects probit results with Free Treatment Period 4 the omitted category. We see that most coefficients are negative, suggesting that regular usage was generally highest for those who received stoves for free in mid-2013 and were subsequently monitored in period 4. However, with few exceptions, the estimates are insignificant.

Such results are difficult to directly interpret. We therefore conduct χ<sup>2</sup> tests for differences in coefficients. We find no statistically significant differences in Period 5 treatment coefficients regardless of our temperature cutoff definition. This suggests that any differences in treatment effects that were observed during the first year are not persistent by year 3. We also find basically no statistical differences between periods 3 or 4 and period 5 regardless of treatment or cooking event definition.<sup>10</sup> We do find evidence of increased regular use over time, which we term persistence, when comparing periods 1 and 2 with period 5, however, for Pay Treatment for all three definitions of cooking events (p<0.001). Free treatment households have significantly more regular usage in period 5 than in period 1 for the 40 and 45-degree cutoff definitions (p <0.05 and p<0.01).

> 10 The only exception is comparison of period 4 and 5 for the Incentive Treatment with cooking event cutoff of 45 degrees Celsius, where usage in period 5 is significantly more than period 4 (p <0.10).

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Incentive Treatment households also show evidence of persistence vis-à-vis period 1, with the 45 and 60-degree cooking event definitions (p<0.10 and p<0.05 respectively).

This long-run persistence compared with early periods is similar to our previous results, which suggested that regular usage on average increased through period 4 for Free Treatment and also for Pay Treatment, which had very low regular usage in period 1 (Beyene et al., 2015; Bluffstone et al., 2018). Results from 2016 suggest that average usage has leveled out, but there has been little of the retrenchment discussed in section 2.

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Table 5. Random effects probit of use of Mirt stove at least twice per week with three cooking event thresholds

||40 Degrees C|45 Degrees C|60 Degrees C|
|---|---|---|---|
||threshold|threshold|threshold|
|Incentive Period 1|-0.445|-0.260|-0.708|
||(0.342)|(0.303)|(0.300)**|
|Incentive Period 2|<br>-0.189|<br>-0.083|<br>-0.282|
||(0.347)|(0.308)|(0.298)|
|Incentive Period 3|-0.177|-0.120|-0.239|
||(0.337)|(0.298)|(0.287)|
|Incentive Period 4|<br>-0.253|<br>-0.239|<br>-0.430|
||(0.343)|(0.303)|(0.293)|
|Incentive Period 5|-0.452|0.225|-0.221|
||(0.373)|(0.327)|(0.310)|
|Pay Treatment Period 1|<br>-1.317|<br>-1.163|<br>-1.197|
||(0.350)***|(0.312)***|(0.307)***|
|Pay Treatment Period 2|<br>-1.039|<br>-0.914|<br>-1.227|
||(0.343)***|(0.306)***|(0.307)***|
|Pay Treatment Period 3|<br>-0.208|<br>-0.131|<br>-0.551|
||(0.334)|(0.294)|(0.286)*|
|Pay Treatment Period 4|-0.251|-0.318|-0.461|
||(0.337)|(0.297)|(0.286)|
|Pay Treatment Period 5|<br>-0.141|<br>-0.023|<br>-0.503|
||(0.374)|(0.323)|(0.317)|
|Free Treatment Period 1|-0.660|-0.606|-0.637|
||(0.275)**|(0.257)**|(0.252)**|
|Free Treatment Period 2|<br>0.029|<br>-0.042|<br>-0.007|
||(0.267)|(0.252)|(0.243)|
|Free Treatment Period 3|0.268|0.245|0.068|
||(0.264)|(0.246)|(0.237)|
|Free Treatment Period 5|<br>-0.054|<br>0.239|<br>-0.266|
||(0.335)|(0.296)|(0.290)|
|Group training dummy|<br>Yes|<br>Yes|<br>Yes|
|<br>Socio-economic variables|Yes|Yes|Yes|
|Cooking characteristics|Yes|Yes|Yes|
|<br>Constant|-0.161|-0.358|-0.480|
||(0.651)|(0.552)|(0.529)|
|N|1,341|1,338|1338|

* _p_ <0.1; ** _p_ <0.05; *** _p_ <0.01.  Robust standard errors in parentheses. Free treatment period 4 is the reference group.

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The Heckman sample selection model, which adjusts for dis-adoption and is presented in column 3 of Table 6, presents a picture that is very similar to the random effects probit results. χ<sup>2</sup> tests for differences in coefficients again show no period 5 differences across treatments; adjusting for dis-adoption, any short-run differential effects are therefore found not to be persistent in the very long run. In the Heckman model, Pay Treatment usage is greater in period 5 than either period 1 (p<0.01) or period 2 (p<0.10), but the same as periods 3 and 4. Free Treatment usage is statistically similar across all periods, as is Incentive Treatment, except for period 3, where period 3 usage is statistically greater than period 5 (p<0.05). The Heckit model shows persistence for Pay Treatment vis-à-vis period 1 (p<0.01) and period 2 (p<0.05), but no other significant results.<sup>11</sup>

> 11 The Heckit model with 45 degree Celsius cutoff indicates persistence for Pay Treatment vis-à-vis periods 1 and 2 (P<0.01). We also find persistence compared with period 1 for Free Treatment (p<0.05) and Incentive Treatment (p<0.05).  The Heckit model would not converge with a 60 degree Celsius cooking event definition.

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Table 6. Heckman probit (Heckit) and Heckman selection models assuming 40 degree Celsius definition of cooking events

||Heckit|H|eckman|
|---|---|---|---|
||(Regular use of<br>|(Actual frequenc|y of stove use per week)|
||≥ 2x/week)|||
|Incentive Period 1|-0.209<br>|-0.943<br>||
||(0.205)|(0.320)***||
|Incentive Period 2|-0.049|-0.713||
||(0.207)|(0.389)*||
|Incentive Period 3|-0.023|-0.011||
||(0.199)|(0.421)||
|Incentive Period 4|0.003|-0.449||
||(0.200)|(0.395)||
|Incentive Period 5|-0.115|-0.783||
||(0.232)|(0.360)**||
|Pay Treatment Period 1|-0.688|-1.376||
||(0.2090<sup>***</sup>|(0.329)***||
|Pay Treatment Period 2|-0.484|-1.148||
||(0.202)<sup>**</sup>|(0.345)***||
|Pay Treatment Period 3|-0.236|-0.379||
||(0.197)|(0.346)||
|Pay Treatment Period 4|-0.199|-0.586||
||(0.199)|(0.339)*||
|Pay Treatment Period 5|-0.046|-0.672||
||(0.219)|(0.340)**||
|Free Treatment Period 1|-0.377|-0.863||
||(0.200)<sup>*</sup>|(0.335)***||
|Free Treatment Period 2|-0.110|-0.551||
||(0.201)|(0.338)||
|Free Treatment Period 3|0.193|0.150||
||(0.202)|(0.389)||
|Free Treatment Period 5|-0.074|-0.337||
||(0.239)|(0.394)||
|Group training dummy|Yes||Yes|
|Socio-economic variables|Yes||Yes|
|Cooking characteristics|Yes||Yes|
|Constant|0.002|2.013||
||(0.239)|(0.481)***||
|N|1498||1,498|
|Wald test of independent<br>equations|Prob > Χ<sup>2</sup>= 0.42|Prob|> Χ<sup>2</sup>= 0.49|

* _p_ <0.1; ** _p_ <0.05; *** _p_ <0.01.  Robust standard errors in parentheses. Free treatment period 4 is the reference group. Selection equation presented in Table 2.

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# 5. **Discussion**

Sustained use of improved technologies, such as biomass cookstoves, is critical to the success of promotion programs. Our results suggest that 3.5 years after receiving the stove, which is close to the expected 5-year lifespan of the stove, about 62% of households covered by the survey still have their Mirt stoves in place, which appears to be quite high. Among those who still have their stoves, the average frequency of stove use in period 5 (i.e. 2016) is no different than the latter part of the first year (periods 3 and 4), but in several cases greater than shortly after initial distribution (periods 1 and 2). This suggests that, even after 3.5 years, the Mirt stove still provides positive net benefits to users. At a contemporary cost of $12.00 and considering the benefits of Mirt stove use, which include fuelwood savings, this seems like a good value to users and to institutions interested in promoting the technology.

We find little systematic relationship between treatments and retention of the stove, which suggests that abandonment is due to reasons other than our randomized treatments. Based on our endline survey, most who dis-adopted their stoves reported that it was because their Mirt stoves broke and therefore either were inconvenient to use or could not be used. People therefore do not seem to have abandoned the Mirt stove simply because they did not like it. Breakage after 3.5 years is not unexpected given that the estimated lifespan is about five years.

Analysis of regular stove use, defined as use of the stove at least twice per week, suggests no differences across treatments 3.5 years after initial distribution. After such a long time, we find that initial treatments do not matter. We also examine effects across time by treatment and find that households who were randomly required to pay a subsidized price for the stove show more consistent increases in regular usage regardless of model or cooking event definition (40, 45 or 60 degrees Celsius) between the two earliest periods and the endline. Bluffstone et al. (2018), which 24
extended the analysis presented in Beyene et al. (2015) using similar data but covering a shorter period than the current study, concluded that Free Treatment is most effective at promoting sustained and increased long-run usage, because Pay Treatment households initially on average used the Mirt stove so much less than those who randomly received the other two treatments. In the very long run, however, we find that Pay Treatment households have continued to increase their average regular usage, with period 5 average usage virtually identical to free treatment. As initial average Pay Treatment regular usage was so low, we therefore find dramatic increases over the life of our study.

# 6. **Conclusions**

This paper analyzes the extent to which the Mirt stove continues to be regularly used 3.5 years after first being randomly distributed to 360 households in three regional states in rural Ethiopia. We also examine the long-run effects of different distribution methods, which were subsidized, for free and user incentivized, applied in a randomized field experiment at the time the Mirt stoves were distributed in summer 2013.

The main conclusion of this paper is that households in rural Ethiopia on average regularly used the Mirt stove – unless it broke – 3.5 years after they were randomly chosen to receive it. This is an important finding that points to the enduring positive net benefits that users receive from the stove compared with exclusive use of the three-stone tripod. This contrasts to other studies where widespread abandonment occurred long before stove life was complete (e.g. Hanna et al., 2016). That the stove is quite cheap and can provide fuelwood savings benefits (Gebreegziabher, 2018) over such a long timeframe highlights the benefit of promoting it.

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In the longer run, effects of monetary treatments connected to stove provision appear to be relatively unimportant. While requiring users to pay may perhaps have created disgruntlement early on that depressed usage (e.g. see Beyene et al., 2015) and reduced total fuelwood savings for Pay Treatment households, regular usage appears in the very long run to be driven by the technical merits of the stove. As the end of the Mirt stove life approaches, regular usage is high and similar across treatments.

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