From 3,600 Participants to Millions: The Investment Case for Scaling Digital Depression Treatment

In August 2023, a nonprofit called Kaya Guides began enrolling its first participants in India. The program it was delivering — WHO Step-by-Step, a five-session behavioral activation program delivered via WhatsApp — had been tested in five randomized controlled trials and shown to produce outcomes comparable to in-person therapy. The cost per year of healthy life gained was approximately $97.

By mid-2024, Kaya had served approximately 3,600 participants. The organization was working through the hard problems of early-stage scale: how to recruit and retain lay counselors at volume, how to build technology systems that could handle larger participant flows, how to maintain program fidelity while adapting to diverse local contexts.

The distance between 3,600 participants and “millions” — the scale at which the program could make a meaningful dent in the global depression burden — is not primarily a scientific or programmatic question. The evidence is in. The model is validated. The distance is a funding question.

This post makes the investment case for closing that gap.

The Problem at Scale

Depression affects more than 300 million people globally. In low- and middle-income countries — where Kaya operates and where the Step-by-Step model was developed and tested — approximately 75 percent of people with depression receive no treatment. The primary reason is not cost, not political will, and not lack of demand. It’s workforce: low-income countries have an average of 1.1 mental health workers per 100,000 people, compared to 67.2 in high-income countries.

That workforce gap cannot be closed on any timeline that matters for people suffering today by training more psychiatrists. Psychiatric training takes a decade. The institutional infrastructure to deploy and retain specialists in low-income settings doesn’t exist. And even if it did, the economics of specialist-delivered care make it unaffordable for the majority of the population in the countries with the greatest need.

The solution that the evidence supports is a fundamentally different delivery model: structured digital content for the therapeutic intervention, combined with lay counselor support for the human contact that research consistently shows is essential for effectiveness. One counselor, with appropriate training and supervision, can support approximately 400 participants per year. That ratio makes mass scale conceivable in a way that specialist-dependent models never can.

The Evidence Foundation

Investment cases built on weak evidence are speculative. The case for Kaya is built on one of the strongest evidence bases in global mental health.

WHO Step-by-Step has been evaluated in five randomized controlled trials across Lebanon, China, Pakistan, Egypt, and South Africa — a total of approximately 2,210 participants. The trials used standardized depression outcome measures, robust randomization, and appropriate controls. The pooled effect size is 0.78, in the medium-to-large range. For reference, in-person cognitive behavioral therapy has an effect size of approximately 0.99. The difference is not statistically significant.

This evidence base — five RCTs across five different countries and cultural contexts — is exceptional by the standards of global health philanthropy. Many high-profile global health programs have been scaled on the basis of one or two trials, often in a single context. Step-by-Step has been tested more rigorously than almost any comparable intervention.

The consistency of results across diverse settings — from Syrian refugee camps in Lebanon to urban communities in South Africa to rural populations in Pakistan — provides strong grounds for confidence that the program will generalize to new contexts as Kaya expands geographically.

The Unit Economics

Kaya’s cost model has been developed with the kind of rigor that serious funders should expect. Here are the key figures:

Total program cost at scale: approximately $1.3 million per year. This figure includes counselor compensation, technology infrastructure, training and supervision, program administration, and organizational overhead.

Counselor-to-participant ratio: one counselor per approximately 400 enrolled participants per year. Each counselor conducts weekly 15-minute check-in calls and provides the human support component that research shows is essential for program effectiveness.

Cost per DALY averted: approximately $97. This is calculated using the full program cost and conservative estimates of depression burden reduction per participant, accounting for completion rates and effect sizes from the RCT evidence.

Cost per WELLBY: approximately $25. Using the wellbeing-adjusted life year framework — which measures subjective wellbeing improvement rather than disability reduction — the cost-effectiveness ratio is even more favorable.

Both figures represent exceptional value by any standard in global health philanthropy. The $97/DALY figure is competitive with malaria bed nets, vitamin A supplementation, and other interventions that appear at the top of cost-effectiveness rankings. The $25/WELLBY figure is among the lowest ever recorded for any wellbeing intervention.

The Household Multiplier

These headline figures, compelling as they are, understate the true cost-effectiveness of the program. Research on Step-by-Step found that household spillover effects — improvements in the wellbeing of family members of program participants — account for approximately 16.24 percent of total program impact.

Depression doesn’t just affect the person who has it. It affects partners, children, parents. When a parent’s depression improves, children’s wellbeing improves. When a partner’s depression improves, relationship quality improves. These effects are real, measurable, and not captured in the individual-focused DALY or WELLBY calculations.

Accounting for household spillovers would reduce the effective cost per DALY and cost per WELLBY further — making an already exceptional investment case even stronger. Funders who think in terms of total societal impact rather than narrowly individual health outcomes will find the case for Kaya even more compelling when these effects are included.

The Path from 3,600 to Millions

What does the scaling roadmap actually look like? Ambitious Impact’s research identified ten priority countries for Step-by-Step expansion: Pakistan, China, Nigeria, Bangladesh, Indonesia, Egypt, Brazil, Tajikistan, Ethiopia, and Malaysia. These were selected based on disease burden, WhatsApp penetration and digital infrastructure, regulatory environment, and absence of existing high-quality programs serving the target population.

The path to millions of participants requires several parallel tracks:

Counselor recruitment and training at volume. Scaling from 3,600 to millions of participants requires building large cohorts of trained lay counselors in multiple countries. This is the central operational challenge and the primary cost driver. Kaya’s model involves recruiting from local communities, providing structured training, and maintaining ongoing supervision to ensure quality.

Technology infrastructure. WhatsApp delivery is the program’s core distribution mechanism. Scaling to millions of participants requires technology systems that can manage participant onboarding, module delivery, progress tracking, and counselor-participant matching at volume. These systems need to be robust, secure, and adaptable to different regulatory environments.

Cultural adaptation. While the core Step-by-Step content has been developed and tested in multiple contexts, expansion to new countries requires localization — translation, cultural adaptation of examples and scenarios, and validation with local populations. This is programmatic work that requires time and resources but doesn’t require re-establishing the evidence base from scratch.

Health system partnerships. For the program to reach its full potential, it needs referral pathways — ways to connect participants who need more intensive support than Step-by-Step provides to the appropriate level of care. Building these partnerships with local health systems, NGOs, and government programs is essential for responsible scale.

Impact measurement. At scale, maintaining rigorous impact measurement is both more important and more challenging than at pilot scale. Kaya will need systems for tracking outcomes, evaluating program quality, and identifying what’s working and what needs adjustment across diverse contexts.

The Funding Need

Kaya is currently in a high-leverage stage of development. The model has been validated. The founding team has been built. The first cohort of participants has been served, generating operational learning that will inform the organization’s growth. What constrains further expansion is funding.

Early-stage capital in this context is particularly valuable for several reasons:

First, it enables geographic expansion to new countries — where the marginal impact of reaching an underserved population is highest. The first participants served in a new country are, by definition, people who had no access to any comparable program before.

Second, it funds the organizational learning that will reduce per-participant costs over time. Building efficient counselor training pipelines, technology infrastructure, and operational systems requires upfront investment that pays dividends at scale.

Third, it provides the track record that enables future fundraising from larger institutional funders — governments, development finance institutions, major foundations — who require demonstrated operational capacity before committing significant resources.

Donors who give now are providing capital at the moment when it has the highest marginal impact on Kaya’s trajectory. They are also, by doing so, helping to build the evidence base for a funding category — guided digital mental health for depression in LMICs — that remains underfunded relative to its potential.

The Comparison to Alternatives

No investment case is complete without asking: compared to what?

For funders with portfolios that span global health, the relevant comparison set includes the highest-performing interventions in the space. Malaria bed nets cost approximately $50-100/DALY in high-transmission settings. Tuberculosis treatment costs approximately $100-300/DALY. Childhood vaccination programs vary widely but generally fall in the $50-200/DALY range.

Step-by-Step at scale — $97/DALY — is directly competitive with these benchmarks. It operates in a cause area (mental health) that receives a fraction of the funding per unit of disease burden that these more established areas receive. The opportunity for a funder to achieve outsized impact by moving resources into an underfunded but highly cost-effective area is precisely what the evidence-based philanthropy framework is designed to identify.

For funders whose primary metric is subjective wellbeing rather than disability-adjusted life years, the comparison is even more favorable. At $25/WELLBY, Step-by-Step outperforms most economic development, education, and health interventions evaluated under the WELLBY framework.

The Verdict

The investment case for scaling Kaya Guides and WHO Step-by-Step is, by the standards that serious global health philanthropy applies, exceptional.

The evidence base is strong — five RCTs across five countries, consistent results, effect sizes comparable to in-person therapy. The cost model is rigorous. The cost-effectiveness ratios are competitive with the most celebrated interventions in global health. The organization is at an early stage where donor capital has maximum marginal impact. The addressable population — hundreds of millions of people with depression and no access to care — is vast.

From 3,600 participants to millions is not a scientific problem. It’s a resource allocation problem. The evidence says it’s solvable. The organization to do it exists. The question is whether the funding community will recognize the opportunity and act on it.

To explore how you can support the scaling of WHO Step-by-Step through Kaya Guides, visit besidehealth.org.