Application of the Limited Enthusiasm Model with Reversion, Written in 2022.

Baptist churches in the UK are a protestant denomination that originated in the English Separatist movements of the 1600s. They believe that the local church is independent, governed by the whole congregation, and that baptism is for believers only (Wikipedia). There are several different Baptist denominations in the UK. The largest is the Baptist Union of Great Britain. However, there are also separate unions in Wales, Scotland and Ireland, and others, such as Grace Baptists. This analysis investigates the decline of UK Baptist churches.

Estimating Model Parameters

I will use the membership data of all UK Baptist churches to estimate the parameters of the Limited Enthusiasm Model with Reversion. Using this cut-down version of the Demographics Model avoids estimating values for child retention among church members, hardening rates etc. There is no information about these values for the Baptists. The reversion model has only five parameters:

  1. Reproduction Potential
  2. Duration Enthusiastic
  3. Loss Rate
  4. Fraction of Converts who Become Enthusiasts
  5. Initial Fraction of Enthusiasts in the Church

The key parameter is the reproduction potential. If this potential is less than one, the Baptist’s decline leads to extinction.

Calibration Strategy

The best fit between data and model is found using least squares. Avoiding systematic deviations from the data can help reduce the number of best fits. To help find the most suitable parameter values, I vary parameters 3-5 above and optimise for 1-2, the reproduction potential and duration enthusiastic. Out of this optimisation set, I count how many indicate the church will become extinct. Although these parameter values cannot be determined with certainty, the likelihood of extinction is more robust.

Membership 2000-2019

I took the membership data for the UK Baptist churches from Brierley (2008-2020).

Every optimisation indicates that the UK Baptists will become extinct, but at a point much further in the future than other declining churches.

Indeed, Baptist decline is sufficiently slow that it is reasonable to assume that there are many stable and growing congregations making up these figures. Thus, a return to growth is both plausible and achievable.

A typical scenario is given in figure 1. Note that the rate of decline of the Baptist churches is increasing. Why could this be? Firstly, the number of enthusiasts may be declining because they are failing to reproduce themselves out of the new converts. Secondly, it could be an ageing effect following an earlier period of higher conversions. Thirdly, the enthusiasts may be losing their effectiveness. The model parameters I state assume the first reason.

Limited Enthusiasm model with Reversion and UK Baptist churches
Figure 1: Data Fit for UK Baptist Church Membership and the Limited Enthusiasm with Reversion Model

Figure 1 uses a typical reproduction potential of 0.95. Although this value indicates future extinction, it is higher than other declining churches. A renewal movement among Baptist churches could tip this reproduction potential to a value over one, leading to growth.

Range of Optimised Parameters

The optimisations indicate a range of possible parameter values:

Reproduction Potential0.7–1.0
Duration Enthusiastic0.3–9.0 years
Loss Rate
(Reversion and Deaths)
Fraction of Converts who Become Enthusiasts10%-50%
Initial Fraction of Enthusiasts in the Church1%–7%
Model Parameters for UK Baptist Churches

The wide range of parameters reflects difficulties in understanding the dynamics of Baptist membership. On average, they have a younger demographic than other denominational churches. Thus, it is likely the loss rate is lower due to fewer deaths. In that case, losses of 6-7% are unlikely, which would give a reversion rate at the lower end of the 0.7-1.0 range. Without inflow and outflow data, it is impossible to be more precise.

Possible Extinction Date

Although the model predicts extinction, it does not indicate an extinction date. The model contains exponential decline because it does not capture the effects of ageing. If the Limited Enthusiasm model is used, then by 2040, the church will have dropped to around 100,000 members, regardless of the optimisation parameters used, figure 2. However, if ageing is included, this figure is likely to be lower.

Figure 2: Projected Future Membership for UK Baptist Churches

If I assume ageing is the dominant factor, then decline follows a straight line. Figure 3 shows forecasts using linear laws. If I use the data from 2000 to 2019, the extinction date is 2085. However, if the steeper decline from 2010 onwards is used, extinction is earlier in 2065.

Figure 3: Linear Fit to UK Baptist Church Membership Data

The likely behaviour is somewhere between those of figures 2 and 3. Baptist churches will survive to the end of the century but in the very low tens of thousands. However, with a current reproduction potential not far below unity, the church should grasp the prospect that these negative scenarios need not happen and that they can return to growth through revival and renewal.

Long–Term View

Baptists in the UK have been declining since 1910, figure 4. Its decline has been slower than most other denominations, probably because it contains a larger proportion of stable and growing congregations than most denominations. Nevertheless, the long term decline indicates prevailing structural weaknesses within the Baptist denomination. Identifying and dealing with those weaknesses is essential to halting decline.

Figure 4: Membership of UK Baptist Churches