Sebastian Tonke

4) Next week, I’m thrilled to begin a new chapter as a tenure-track professor at @tum.de. I’m excited to build something new, to work with outstanding colleagues and students, and to contribute to its dynamic and world-class academic environment.

3) A heartfelt thank you to everyone who shared this journey, and especially to Matthias Sutter for his leadership, vision, and support that made so much possible for the institute and our research group. I will always visit with a smile on my face.

2) I’m incredibly grateful for the time I’ve spent here. Not only for the scientific excellence, but also for the people who made it outstanding. A truly collegial atmosphere, mutual support for our research projects, and outstanding guests from around the world made this place very special for me.

Today marks my last day at the Max Planck Institute for Behavioral Economics @econmpi.bsky.social and its beautiful building.

A Large-Scale Field Experiment to Reduce Nonpayments for Water: From Diagnosis to Treatment Abstract. In a field experiment among 9,823 customers of the Namibian water utility, we implement interventions to reduce nonpayments. The interventions are based on diagnostic surveys to identify key obstacles to payments. They address informational frictions and apply psychological commitment techniques to narrow the gap between customers’ willingness to pay and actual payments. Initially, payments increase by 29% to 55%, making the interventions highly cost-effective. Removing informational frictions has a lasting impact, but the commitment techniques produce only short-term effects. We demonstrate the effectiveness and limitations of behavioral interventions in settings where heavy-handed tools (e.g., disconnecting nonpayers) are difficult to implement.

From behavioral diagnosis to highly cost-effective interventions to tackle non-payment for public utilities. In the September issue, by Bettina Rockenbach, Sebastian Tonke, Arne Weiss zurl.co/5yS0t

So:

✅ Identity can be shaped

✅ Actions ONLY shape how we see ourselves when the identity-action link is salient.

✅ Linking behavior to identity creates lasting change.

Paper ➡️ [https://tinyurl.com/3b7jha2b]

9/9

The result?

📉 Non-payment for water nearly eradicated
💰 ROI: over 3,000%
🪙 Cost: ~22 cents per household
🧠 And people liked the messages

8/9

Why?

Identity appeals induce a permanent intrinsic motivation: Individuals continue to see their actions as a credible signal about their identity.

7/9

And long term?

⚠️ Simple reminders backfired. Payments dropped below even the control group after the intervention ended. A zero effect over the span of a year.

✅ Identity appeals, by contrast, sustained high payments.

6/9

👉 Only identity appeals changed how people saw themselves.

People who didn’t pay under identity appeals felt less like responsible citizens afterward. They updated their self-perception based on their actions.

No change under simple reminders.

5/9

I tested two kinds of messages placed on the water bills:

✅ Identity appeals
→ Creating a link between paying and being a “responsible citizen.”

❌ Simple reminders
→ No mention of identity

Both boosted short-term payments.

But the long-term effects? Fundamentally different.

4/9

To find out, I ran a large-scale field experiment:

📊 11,434 households
📬 29,677 hand-delivered messages
💧 A public water utility struggling to collect water bill payments

3/9

Our identity (or self-perception) influences a host of behaviors such as educational investments, political participation, and also civic duties.

But here’s a question:

👉 Can actions change how we see ourselves?

And if so… can policymakers use that to induce sustained behavioral change?

2/9

🤔 How do people form beliefs about who they are?

🤔 Can identity be shaped to change economic behavior?

A 🧵 on my paper: “Shaping Identity” recently accepted at JPE Micro!

#econsky
#publicationalert
1/9

Very much looking forward to this! Don't forget to submit your paper or abstract by May 15!

❗Deadline Approaching for SEEDEC 2025!

Don't miss your chance to register for the Symposium on Economic Experiments in Developing Countries (SEEDEC 2025) in Bonn, Germany!

⏳ Registration deadline: March 1, 2025

🔗 www.nhh.no/en/research-... @vincentsomville.bsky.social

! Call for Papers for the VfS Annual Conference 2025 from 14th to 17th September ! This year's VfS Annual Conference will take place at the @unicologne.bsky.social and @wisocologne.bsky.social and is organized by our Cluster member @fixbierbrauer.bsky.social. Submission deadline: 1 March. More info👇

📣📣📣
#EconSky

Inspired by @tapiorasanen.bsky.social, here is a starter pack for economists conducting field experiments 🤓🫶

Please let me know who is missing – and share widely! 🚀

go.bsky.app/9hev4gN

We're hiring! #econsky #econjobmarket

Predoctoral Research Assistant (m/f/div) for Project on International Educational Migration

We are hiring a Predoc! Join our international research team at the MPI to work on an RCT focused on international educational migration. Based in Bonn, Germany, with competitive pay and exciting opportunities for professional development. Apply here: career.coll.mpg.de/jobposting/c...

Saving water via text message In Namibia, providing a short list of specific saving strategies reduced water consumption by 5% while simply raising awareness and asking households to find their own strategies was ineffective

🆕 In Namibia, providing a short list of specific saving strategies reduced water consumption by 5% - simply raising awareness & asking households to find their own strategies was ineffective.

Sebastian Tonke outlines evidence on effectively promoting water conservation: voxdev.org/topic/energy...

Please RT: Our fundraising at @malengo has been slow! We want to support as many students as possible on their journey from Uganda to a Bachelor's degree in Germany. Please support us! Donations are tax deductible in the US and Germany. Details at malengo.org/donate. Thanks!

So great to see this published online at the #JDE 🥳

👉 RCT to curb water demand in Namibia during severe #waterscarcity.
👉 Providing a short list of actionable and specific saving tips reduces consumption by 5%.

#Sustainability #ClimateCrisis #boost
Get the paper here (OA) 👉tinyurl.com/23fxufzs