How Does the SALT Index Compare to Other Spiritual Formation Research?

The Center for Spiritual Fitness recently released What is the SALT (Scripture Absorption and Life Transformation) Index, which describes the development of a new tool for assessing spiritual formation in Christian ministry.  That paper’s development resulted from a U.S. General Population survey using the SALT Index. We propose that the SALT Index represents a significant advancement in assessing Christian discipleship and spiritual health. In this paper, we compare the SALT Index to other research, including studies published by Lifeway Research, the Barna Group, and the American Bible Society.

Each study has a slightly different focus. For example, Lifeway Research’s State of Discipleship Study examines beliefs and behavior gaps among church attenders. Barna’s studies consider cultural shifts and engagement trends in the U.S. population. The SALT Index is designed to provide a global and generalizable measure of spiritual formation that can be used across a wide variety of contexts from the general population to individual churches to broader evangelistic ministry efforts. The SALT Index distinguishes itself from other measures in these key ways:

·         Outcomes-based methodology

·         Broad scope

·         Empirical rigor

·         Practical applications

·         Ability to bridge gaps in existing research

This remainder of this paper expands on these distinctions, providing readers with a picture of where the SALT Index fits in the existing spiritual formation research landscape.

Descriptive or Input-Focused Assessments vs. Outcomes

In developing the SALT Index, we sought to shift the paradigm from merely counting affiliations, beliefs, or practices to quantifying actual life transformation. A significant amount of the research about Christian faith asks if people identify as Christian, attend church, or engage in spiritual habits. The SALT Index probes deeper into observable, evidence-based outcomes like whether faith leads to changed behaviors (e.g., forgiveness, integrity, service, relational healing), disciple-making, and external validation (e.g., others noticing positive changes). For instance, the 2025 baseline reveals that only ~40% of self-identified Christians show clear outward signs of spiritual transformation, and very few actively mentor others. This "outcomes lens" ties directly to biblical concepts such as the "Fruit of the Spirit" and the command to “make new disciples” in the Great Commission, providing concrete metrics to evaluate true spiritual health.

Lifeway's State of Discipleship study (2025) surveyed Protestant pastors and churchgoers on self-assessed spiritual characteristics. The results are descriptive and input oriented. For example, they report an average score of 68/100 across eight traits, with evangelism at a failing 54.8/100. This study notes the lack of measurement in churches noting that only 30% have methods to track growth. Yet the State of Discipleship study largely remains within the walls of churches and relies on internal self-reports.

Barna's studies, such as the 2025 State of the Bible (in partnership with the American Bible Society) and Top Trends of 2025, emphasize descriptive trends in Bible engagement and discipleship (e.g., Bible reading up among Millennials and Gen Z, with 50% of Millennials reading weekly). Their State of the Church 2025 initiative measures human flourishing across relational, spiritual, physical, emotional, vocational, and financial dimensions, noting increases in belief in Jesus (fueled by younger adults) but a "discipleship crisis" with mentoring uncommon and Bible engagement inconsistent. While Barna highlights positive shifts (e.g., Gen Z driving Bible exposure) and calls for sustainability in pastoral flourishing, it remains trend-focused and heavily focused on “spiritual inputs” such as church attendance and Bible reading. These measures alone don’t tell us anything about transformation outcomes or external fruit.

The academic literature on spiritual formation provides little guidance for those wanting to know how the Church is doing in making disciples. In general, these studies conceptualize spiritual growth diversely (e.g., relational spirituality, identity integration, vocational practices). While some studies demonstrate a positive link between faith and health outcomes, it's often theoretical or context-dependent, heavily reliant on qualitative data, and limited by small sample sizes.  

In essence, the SALT Index measures impact (e.g., "Did faith lead to forgiveness or mentoring?"), over inputs or trends.

Narrow or Niche Samples vs. Broad, Representative Samples

To validate the SALT Index, we conducted a large-scale, nationally representative survey of U.S. adults (n = 6,037).  This study captures the general population, not just active churchgoers or specific subgroups and reveals critical gaps like the "belief-practice divide" (e.g., 60% identify as Christian, but only 35% read Scripture regularly) and generational trends (e.g., younger Christians are devout but less evangelistic). This population-level baseline allows for testing revival claims empirically (e.g., if revival is real, SALT scores should rise over time).

In contrast, Lifeway’s State of Discipleship study is limited to Protestant churchgoers and pastors, missing the broader societal context. It confirms discipleship deficits, but doesn't benchmark against non-churchgoers or the full U.S. population, leading to potential echo-chamber biases. SALT's general-population approach exposes nominalism (e.g., half of Christians disconnected from disciplines) that Lifeway might overlook by sampling only engaged attendees.

Barna's research often uses nationally representative samples (e.g., their American Worldview Inventory and State of the Church surveys), similar to the SALT Index study, and measures broad trends like generational shifts and church effectiveness in discipleship. However, Barna's scope is more segmented by topic and focuses on snapshots of engagement or beliefs. It doesn't provide a single, holistic index that links engagement directly to transformation across the general population.

Static or Qualitative Insights vs. Empirical Rigor and Longitudinal Potential

The SALT Index is designed to measure changes over time. The 2025 US General Population study serves as a quantitative baseline for tracking progress over time. For example, future surveys could measure if spiritual practices and life transformation increases.

Lifeway uses surveys and indices (e.g., 8 spiritual characteristics scored out of 100) but is more cross-sectional and self-assessed, with less emphasis on external validation. It identifies needs (e.g., refocusing on formation) but doesn't offer a tool as adaptable or baseline-oriented as the SALT Index for ongoing measurement.

Barna excels in longitudinal tracking (e.g., annual American Worldview Inventory over six years, State of the Bible trends showing Bible reading fluctuations), with rigorous, data-backed insights. However, Barna's research products are often segmented reports rather than a unified index, and while they measure spiritual formation in many ways, they don't tie it to observable life changes.  

Theoretical or Limited Recommendations vs. Practical Applicability and Strategic Insights

The SALT Index was created to directly inform action for leaders, funders, and policymakers. It grew from a desire to shift from "vanity metrics" (attendance) to outcomes (disciple-making).  By asking "What has become of the harvest?", it challenges overstatements and grounds revival rhetoric in data, fostering a culture of stewardship.

Lifeway studies also offer practical tips (e.g., intentional discipleship plans) but within a church-centric frame.  without SALT's broader implications (e.g., global applicability, AI integration). Similarly, Barna's trends are highly practical for ministry (e.g., fostering relational discipleship for Gen Z resilience, addressing pastoral sustainability), with resources like Barna Access Plus for leaders. Both base their recommendations on observations of inputs and trends, rather than actual outcomes. Moreover, these suggestions rely heavily on products from the same organizations, which in and of themselves haven’t been empirically tested.

Conclusions

This brief review demonstrates the strengths of the SALT Index for understanding and measuring spiritual formation. It overcomes many of the limitations of other survey tools including those from influential organizations such as Lifeway Research and Barna. By emphasizing outcomes, representativeness, rigor, and applicability, SALT provides a defensible baseline for evaluating Christian impact in 2025 and beyond—complementing Barna's cultural insights while surpassing them in depth. It reveals America's faith as "mile wide, inch deep". It also offers hope by showing a path to increasing life transformation. Those involved in ministry, research, or funding will find that adopting SALT-like metrics enables them to "measure what matters” and ultimately yield lasting fruit rather than fleeting activity.

All of these approaches offer valuable insights—Lifeway on churchgoer deficits, the academic literature on contextual mechanisms, and Barna on cultural shifts and engagement trends. The SALT Index fills in a gap in this literature with its outcomes-based methodology, broader scope, empirical rigor, ability to track outcomes longitudinally, and practical applicability.

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