Ncls Research

Introducing the Inflow Outflow Model

When churches grow, many assume good things must be happening. Indeed, church attendance growth has been seen by some as the measure of church health. Where there is decline, it is assumed that the church must be unhealthy in some way.

Yet, NCLS researchers argue that a focus only on numbers can be limited and misleading. Is growth made up mostly of people moving in from other churches? What about attracting newcomers from the community or retaining the children brought up within the church? If a church only pays attention to its overall attendance growth or decline, it can draw wrong conclusions about the true nature of their connection with the community.

Research in Western countries has shown that much of what passes as church growth is actually people moving between churches, or ‘religious musical pews’. Often it is not the inclusion of new believers as in the New Testament. In Australia it has been estimated that only a quarter of all church growth is comprised of people fresh from the community moving into church life.

NCLS Research offers a more sophisticated, holistic and useful way to think about attendance change. The NCLS Inflow Outflow model present attendance change in terms of its various components. This model helps churches to understand whether their growth is a reflection of effectiveness in mission or whether it is being driven by other factors.

Why do churches grow? This question has a very simple answer. Churches grow when inflow exceeds outflow. Overall attendance increases when the number of people arriving at a church is greater than the number of people who leave it.

This paper maps the inflow and outflow for a number of Australian denominations that took part in both the 1996 and 2001 NCLS.

There are three sets of reasons that churches grow and decline; three doors in and three doors out. If we want to better understand how attendance change occurs, we need to measure each of these separately. For each inflow path, there is a matching outflow.

Switching: Attenders switching between churches will affect each one either positively or negatively

Births and Deaths: Children born to church attenders naturally increase the size of the church, but it is whether they can be retained, particularly as they enter the teenage years that ultimately determines whether the church has truly grown from them. The passing of older attenders naturally reduces the size of the churches.

The Front and Back Doors: Newcomers without a background of church involvement comprise an important flow of new life into churches. An equally important flow in the opposite direction are made up by attenders drifting out of church involvement altogether.

The NCLS Inflow Outflow Model of Attendance Change

The NCLS Inflow Outflow Model of Attendance Change
Source: NCLS Research

The Inflow Outflow Model is made up of seven components: three inflow measures, three outflow measures and net attendance change.

Inflow comprises the 3 paths on the left:

  • Switchers In: people arriving from other congregations
  • Young Adult Retention: people brought up in the church
  • Newcomers: people who join with no church background

Outflow comprises the 3 paths on the right:

  • Switchers Out: People leaving for other congregations
  • Deaths
  • Drift Out: People drifting out or leaving church life

The attendance change in a congregation or denomination is the net result of these paths added together. That is, the percent growth or decline over the last five years is the percent of total inflow minus the percent of total outflow.

Calculating the flow between churches

When churches or denominations think about attendance change in terms of its components, they can make more sense of the changes they may be seeing. What percentage of current attenders are newcomers (who had no church background)? How many came from other churches in the last five years? What percentage are youth who chose to stay as they became part of the active adult population of church over that time? Put simply, there are no other sources of church growth except these three!

National Church Life Surveys have been conducted in 1991, 1996 and 2001, measuring these and a host of other features of churches. These figures can be supplied for either a congregation or a whole denomination. The comprehensive and longitudinal nature of the Surveys means that NCLS researchers are in an unmatched position in terms of being able to estimate inflow and outflow for whole denominations. This paper focuses on several denominations or groups, and charts their changes using the inflow outflow model, over the 5 year periods of 1991-1996 and 1996-2001.

Components of this model

Attendance Net Change: The foundation of this model is the net change of attendance over five years – the number that appears under the diagram that indicates overall growth or decline. Careful estimates of church attendance have been collated by NCLS Research over the years. (See Occasional Paper 3: Estimates of Church Attendance 2001). NCLS bases their size estimates from a question answered by the church leadership (and includes the numbers of children). In addition, NCLS obtains size estimates of churches that don’t participate in the survey, to get a more accurate overall picture. Therefore the inflow outflow model begins with a solid estimate of whether a church has grown or declined in a five-year period. This overall percentage growth or decline is listed at the base in the middle of the Inflow Outflow model.

NCLS Inflow and Outflow Model:
A ‘rule of thumb’ The figure for attendance net change shown under each model is the most accurate figure for overall change; the estimates of inflow and outflow shown in the boxes are an approximation of how that change came about.

An important ‘rule of thumb’: The figure for attendance net change shown under each model is the most accurate figure for overall change; the estimates of inflow and outflow shown in the boxes are an approximation of how that change came about. The other figures in the inflow outflow model come from the results of surveying the adult population, or from an additional estimation (such as the expected number of deaths based on the age profile of a denomination). This means they are not as exact, but an approximation of each component that led to the net result we see.

How does NCLS estimate the other components of the model? The extensive nature of each National Church Life Survey allows accurate estimates of people who are currently in a church. It is possible to count the numbers of denominational switchers, retained youth, newcomers to church life, and long-term attenders.

Switchers In: This group includes people who have arrived in the previous five years coming from churches in other denominations.

Young Adult Retention: This is the percentage of people in the church aged 15-19 years old who were also attending the same denomination five years ago. These young people who have stayed with church as they have passed into an age where they typically have more personal choice in the matter are the ‘retained youth’.

Newcomers: Newcomers are the new attenders who have arrived in the last five years and who previously did not attend another church.

Long term attenders: Long term attenders have been part of their current denomination for five years or longer. They have not been part of inflow or outflow and are shown in the large middle box in the diagram.

Helpful hint: if you add these 4 boxes you get 100% - the total adults currently attending church.

The NCLS cannot provide such an accurate count of the 3 boxes on the right hand side of the diagram: those who have switched to other churches, those who have died, or those who have drifted out of church life. However a reasonable estimate of these can still be arrived if participation rates in the survey has been sufficient. In this paper we concentrate on larger groups and denominations for this reason.

Switchers Out: Because so many denominations participate in each NCLS, most of those who have moved to a new denomination are also being counted, and those in non-participating denominations can be estimated to some degree. Therefore at the denominational level a fair estimate of those who have moved to another group can indeed arrived at.

Deaths: The Australian Bureau of Statistics provides mortality rates for each age group across the population. By applying that to the current age profile of each denomination, estimates have been made of likely losses through the deaths of some attenders over the previous five years.

Drift out: This leaves one missing piece – an estimate of the number of people drifting out of church life altogether. This can be estimated by calculating the size of the other flows into and out of church life, and the overall change in attendance between 1996 and 2001. While the result is approximate, it opens up for reflection an important aspect of the churches’ relationship with the wider community.

Adjustment in calculations

The benefit of experience has allowed NCLS researchers to improve the method and accuracy of these calculations. More refined measurements of some groups has been possible in recent years subsequent to earlier work.

To allow comparison, the 1991 to 1996 models have been recalculated using the improved methods. Consequently, the figures presented in this paper supersede any earlier publications (eg Build My Church, 1999). Any differences primarily stem from a revision of the estimation of the youth figures and an improved weighting scheme.

Inflow and Outflow for Denominations or Groupings:

Australian Churches
The Protestant Church in Australia
Pentecostal Churches
Anglican Churches
Assemblies of God
Baptist Church
The Catholic Church
Churches of Christ
Lutheran Church
Presbyterian Church
Uniting Church



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