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Field
Abstract
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Before
This study investigates the motivations behind charitable giving after the provision of a public good, following the approval of a new climate law through a referendum. An environmental NGO is launching its first fundraising appeal after this policy success, creating a setting in which the core policy outcome has already been secured. This context allows us to examine whether post-policy donations are driven primarily by expressive warm-glow motives or by instrumental considerations about continued impact.
We implement a natural field experiment with 3,367 potential donors using a 2×2 design. The first treatment dimension varies the motivational framing of the appeal: the message either emphasizes expressive participation and the symbolic value of being part of a successful civic movement (warm-glow framing), or it highlights the instrumental role of donations in financing concrete follow-up activities and ensuring effective implementation of the law (instrumental framing). The second treatment dimension varies the spatial scope of benefits emphasized in the appeal, focusing either on local benefits for Hamburg or on global climate benefits. This allows us to test whether donors exhibit parochial preferences and whether spatial scope interacts with motivational framing.
Randomization is stratified by past donation behavior, nationality and prior engagement with the NGO. The primary outcomes are the donation decision and donation amount. The experiment provides causal evidence on expressive versus instrumental motivations and on the role of spatial scope and parochialism in pro-environmental giving after a public good has already been provided
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After
This study investigates the motivations behind charitable giving after the provision of a public good, following the approval of a new climate law through a referendum. An environmental NGO is launching its first fundraising appeal after this policy success, creating a setting in which the core policy outcome has already been secured. This context allows us to examine whether post-policy donations are driven primarily by expressive warm-glow motives or by instrumental considerations about continued impact.
We implement a natural field experiment with 3,543 potential donors using a 2×2 design. The first treatment dimension varies the motivational framing of the appeal: the message either emphasizes expressive participation and the symbolic value of being part of a successful civic movement (warm-glow framing), or it highlights the instrumental role of donations in financing concrete follow-up activities and ensuring effective implementation of the law (instrumental framing). The second treatment dimension varies the spatial scope of benefits emphasized in the appeal, focusing either on local benefits for Hamburg or on global climate benefits. This allows us to test whether donors exhibit parochial preferences and whether spatial scope interacts with motivational framing.
Randomization is stratified by past donation behavior, nationality, prior engagement with the NGO, and timing of subscription relative to the approval of the climate law. The primary outcomes are the donation decision and donation amount. The experiment provides causal evidence on expressive versus instrumental motivations and on the role of spatial scope and parochialism in pro-environmental giving after a public good has already been provided
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Field
Last Published
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Before
February 19, 2026 05:25 AM
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After
February 20, 2026 08:44 AM
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Field
Intervention (Public)
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Before
The intervention is a natural field experiment embedded in the environmental organization’s first fundraising campaign following the approval of a new climate law through a referendum. A total of approximately 3,367 individuals from the organization’s contact list, including both past and potential donors, receive one of four versions of a donation request. The experiment follows a two-by-two design.
The first treatment dimension varies the motivational appeal of the message. In the warm-glow condition, the appeal emphasizes expressive participation and the symbolic value of being part of a successful civic movement, highlighting the collective achievement of the referendum. In the instrumental condition, the appeal emphasizes the concrete role of donations in financing follow-up activities and ensuring effective implementation of the law, thereby stressing the tangible impact of contributions.
The second treatment dimension varies the spatial scope of benefits emphasized in the appeal. Half of the messages focus on local benefits for Hamburg, while the other half highlight global climate benefits.
Randomization is conducted at the individual level and stratified by nationality, past donation status, and prior engagement with the organization, ensuring balanced assignment across treatment groups. Each individual receives only one version of the fundraising message through the organization’s standard communication channels.
The intervention is designed to examine why individuals donate after the successful provision of a public good, distinguishing between warm-glow and instrumental motivations and testing for parochial preferences and sensitivity to the spatial scope of benefits through variation in local versus global emphasis.
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After
The intervention is a natural field experiment embedded in the environmental organization’s first fundraising campaign following the approval of a new climate law through a referendum. A total of approximately 3,543 individuals from the organization’s contact list, including both past and potential donors, receive one of four versions of a donation request. The experiment follows a two-by-two design.
The first treatment dimension varies the motivational appeal of the message. In the warm-glow condition, the appeal emphasizes expressive participation and the symbolic value of being part of a successful civic movement, highlighting the collective achievement of the referendum. In the instrumental condition, the appeal emphasizes the concrete role of donations in financing follow-up activities and ensuring effective implementation of the law, thereby stressing the tangible impact of contributions.
The second treatment dimension varies the spatial scope of benefits emphasized in the appeal. Half of the messages focus on local benefits for Hamburg, while the other half highlight global climate benefits.
Randomization is conducted at the individual level and stratified by nationality, past donation status, and prior engagement with the organization, and time of subscription with regards to the laws passing, ensuring balanced assignment across treatment groups. Each individual receives only one version of the fundraising message through the organization’s standard communication channels.
The intervention is designed to examine why individuals donate after the successful provision of a public good, distinguishing between warm-glow and instrumental motivations and testing for parochial preferences and sensitivity to the spatial scope of benefits through variation in local versus global emphasis.
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Field
Experimental Design (Public)
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Before
The study is a natural field experiment conducted during an environmental organization’s first fundraising campaign following the public announcement of the approval of a climate law through a referendum. Approximately 3,367 individuals from the organization’s contact list are randomly assigned to one of four treatment conditions in a two-by-two design. These conditions vary the motivational appeal of the donation request, contrasting a warm-glow appeal emphasizing expressive participation and symbolic support with an instrumental appeal emphasizing the role of donations in supporting implementation of the law, and vary whether the benefits of the climate law are described in terms of local or global impact.
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After
The study is a natural field experiment conducted during an environmental organization’s first fundraising campaign following the public announcement of the approval of a climate law through a referendum. Approximately 3,543 individuals from the organization’s contact list are randomly assigned to one of four treatment conditions in a two-by-two design. These conditions vary the motivational appeal of the donation request, contrasting a warm-glow appeal emphasizing expressive participation and symbolic support with an instrumental appeal emphasizing the role of donations in supporting implementation of the law, and vary whether the benefits of the climate law are described in terms of local or global impact.
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Randomization Method
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Before
Randomization is conducted at the individual level. Each of the 3,367 individuals in the study sample is assigned to one of four treatment conditions in a two-by-two factorial design. Assignment is implemented in Stata using a reproducible random-number seed to ensure full replicability.
Randomization is stratified on two pre-treatment characteristics recorded in the organization’s administrative data:
Past donation status: whether the individual has ever made a prior donation to the organization;
Past engagement: whether the individual has previously interacted with the organization’s communications (e.g., opened or clicked prior messages, or participated in previous actions).
Stratification on these variables ensures balanced assignment across groups that differ in historical involvement with the organization.
Participants do not choose their treatment assignment, and the assignment is not visible to them at any stage. All individuals receive a fundraising message with an identical header, format, and general structure. Only selected lines in the body of the message vary according to the experimental condition. This design eliminates self-selection into treatment and supports unbiased estimation of intent-to-treat effects.
Within each stratum, individuals are assigned with equal probability to one of the four treatment cells (Anonymous–Local, Anonymous–Global, Public–Local, Public–Global). No cluster-level randomization is used.
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After
Randomization is conducted at the individual level. Each of the 3,543 individuals in the study sample is assigned to one of four treatment conditions in a two-by-two factorial design. Assignment is implemented in Stata using a reproducible random-number seed to ensure full replicability.
Randomization is stratified on two pre-treatment characteristics recorded in the organization’s administrative data:
Past donation status: whether the individual has ever made a prior donation to the organization;
Nationality: International or German
Time of subscription: If potential donow subscribed before or after the laws adoption.
Past engagement: whether the individual has previously interacted with the organization’s communications (e.g., opened or clicked prior messages, or participated in previous actions).
Stratification on these variables ensures balanced assignment across groups that differ in historical involvement with the organization.
Participants do not choose their treatment assignment, and the assignment is not visible to them at any stage. All individuals receive a fundraising message with an identical header, format, and general structure. Only selected lines in the body of the message vary according to the experimental condition. This design eliminates self-selection into treatment and supports unbiased estimation of intent-to-treat effects.
Within each stratum, individuals are assigned with equal probability to one of the four treatment cells (Anonymous–Local, Anonymous–Global, Public–Local, Public–Global). No cluster-level randomization is used.
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Planned Number of Clusters
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Before
3367 individuals
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After
3,543 individuals
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Planned Number of Observations
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Before
3367 individuals
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After
3,543 individuals
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Sample size (or number of clusters) by treatment arms
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Before
Approximately equal numbers of individuals are assigned to each of the four treatment arms, with about 840 to 844 individuals per arm, for a total sample size of 3,367 individuals.
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After
Approximately equal numbers of individuals are assigned to each of the four treatment arms, with about 840 to 844 individuals per arm, for a total sample size of 3,543 individuals.
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Power calculation: Minimum Detectable Effect Size for Main Outcomes
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Before
The study is individually randomized with no clustering. The planned sample size is 3,367 individuals allocated approximately equally across four arms in a two-by-two design. The primary analyses estimate the main effects of motivational appeal (warm-glow versus instrumental) and spatial scope (local versus global), as well as their interaction. For the estimation of main effects, observations are pooled across the complementary treatment dimension, yielding approximately half the sample in each main comparison arm.
A formal minimum detectable effect size is not pre specified because it depends on the baseline level and variance of the main outcomes in this fundraising campaign, in particular the donation rate, the distribution of donation amounts, and the variance of link click behavior.
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After
The study is individually randomized with no clustering. The planned sample size is 3,543 individuals allocated approximately equally across four arms in a two-by-two design. The primary analyses estimate the main effects of motivational appeal (warm-glow versus instrumental) and spatial scope (local versus global), as well as their interaction. For the estimation of main effects, observations are pooled across the complementary treatment dimension, yielding approximately half the sample in each main comparison arm.
A formal minimum detectable effect size is not pre specified because it depends on the baseline level and variance of the main outcomes in this fundraising campaign, in particular the donation rate, the distribution of donation amounts, and the variance of link click behavior.
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Field
Intervention (Hidden)
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Before
The study is implemented as a natural field experiment embedded in an environmental organization’s first fundraising campaign following the public announcement of the approval of a climate law through a referendum. The target population consists of individuals on the organization’s contact list, including both potential donors and past donors. A total of 3,367 individuals are included in the randomized sample.
The experiment follows a two-by-two factorial design. The first treatment dimension varies the motivational appeal of the donation request. In the warm-glow condition, the message emphasizes expressive participation and the symbolic value of contributing to a successful civic movement, highlighting the collective achievement of the referendum. In the instrumental condition, the message emphasizes the concrete role of donations in financing follow-up activities and supporting effective implementation of the newly approved law, thereby stressing the tangible impact of contributions.
The second treatment dimension varies the spatial scope of benefits associated with the recently approved climate law. In the local emphasis condition, the donation request highlights benefits for the jurisdiction in which the referendum took place. In the global emphasis condition, the message highlights global climate benefits. Given the characteristics of climate protection, the local and global versions are constructed to describe comparable mitigation and co-benefit outcomes, such as reductions in carbon emissions and associated health improvements, using closely aligned language. The primary difference across conditions is the geographic scope of beneficiaries rather than the type of benefit described.
Randomization is conducted at the individual level using Stata with a fixed random seed. Assignment is stratified by nationality, past donation category, and past engagement with the organization. Past donation is categorized into three groups: no recorded past donation, low past donation, and high past donation, based on the distribution of recorded donation amounts among past donors. Engagement is categorized into low and high engagement based on the median of a pre-treatment engagement measure. Stratification ensures balanced assignment across treatment arms along these dimensions.
Each individual receives exactly one version of the donation request through the organization’s standard communication channels. There is no self-selection into treatment assignment, as the subject line and initial receipt of the message are treatment independent. All analyses are conducted within an intention-to-treat framework based on initial assignment.
The primary analysis estimates the average effects of motivational appeal and spatial scope emphasis on donation behavior, as well as their interaction. Main effects are estimated pooling across the complementary treatment dimension to maximize statistical power. The interaction between motivational appeal and spatial scope captures whether sensitivity to the geographic diffusion of benefits differs between warm-glow and instrumental appeals.
In addition to the factorial treatment effects, the study examines heterogeneity across pre-treatment characteristics, including nationality, past donation category, and past engagement with the organization. These analyses assess whether responses to motivational appeal and spatial scope vary systematically across donor history, engagement levels, and nationality.
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After
The study is implemented as a natural field experiment embedded in an environmental organization’s first fundraising campaign following the public announcement of the approval of a climate law through a referendum. The target population consists of individuals on the organization’s contact list, including both potential donors and past donors. A total of 3,543 individuals are included in the randomized sample.
The experiment follows a two-by-two factorial design. The first treatment dimension varies the motivational appeal of the donation request. In the warm-glow condition, the message emphasizes expressive participation and the symbolic value of contributing to a successful civic movement, highlighting the collective achievement of the referendum. In the instrumental condition, the message emphasizes the concrete role of donations in financing follow-up activities and supporting effective implementation of the newly approved law, thereby stressing the tangible impact of contributions.
The second treatment dimension varies the spatial scope of benefits associated with the recently approved climate law. In the local emphasis condition, the donation request highlights benefits for the jurisdiction in which the referendum took place. In the global emphasis condition, the message highlights global climate benefits. Given the characteristics of climate protection, the local and global versions are constructed to describe comparable mitigation and co-benefit outcomes, such as reductions in carbon emissions and associated health improvements, using closely aligned language. The primary difference across conditions is the geographic scope of beneficiaries rather than the type of benefit described.
Randomization is conducted at the individual level using Stata with a fixed random seed. Assignment is stratified by nationality, past donation category, time of subscription with regards to the adoption of the law and past engagement with the organization. Past donation is categorized into three groups: no recorded past donation, low past donation, and high past donation, based on the distribution of recorded donation amounts among past donors. Engagement is categorized into low and high engagement based on the median of a pre-treatment engagement measure. Time of subscription records if subscirption happened before the laws passing or after. Stratification ensures balanced assignment across treatment arms along these dimensions.
Each individual receives exactly one version of the donation request through the organization’s standard communication channels. There is no self-selection into treatment assignment, as the subject line and initial receipt of the message are treatment independent. All analyses are conducted within an intention-to-treat framework based on initial assignment.
The primary analysis estimates the average effects of motivational appeal and spatial scope emphasis on donation behavior, as well as their interaction. Main effects are estimated pooling across the complementary treatment dimension to maximize statistical power. The interaction between motivational appeal and spatial scope captures whether sensitivity to the geographic diffusion of benefits differs between warm-glow and instrumental appeals.
In addition to the factorial treatment effects, the study examines heterogeneity across pre-treatment characteristics, including nationality, past donation category, time of subscription and past engagement with the organization. These analyses assess whether responses to motivational appeal and spatial scope vary systematically across donor history, engagement levels, and nationality.
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