Edit a smoothing curve in a refinement workflow

Modify a specified interval of a smoothing curve previously added with add_smoothing(). Use a relative adjustment when the existing shape is broadly appropriate, or explicit values and control points when the curve should follow known targets.

Usage

edit_smoothing(
  model,
  model_variable = NULL,
  step = NULL,
  from = NULL,
  to = NULL,
  from_value = NULL,
  to_value = NULL,
  control_positions = NULL,
  control_values = NULL,
  adjustment = NULL,
  slope_adjustment = 1,
  transition = NULL,
  allow_extrapolation = FALSE,
  extrapolation_step = NULL
)

Arguments

model: Object of class rating_refinement, created with prepare_refinement() and containing an existing smoothing step. Ordinary and refitted GLMs are not accepted directly. Legacy smooth and restricted objects are still accepted for backwards compatibility.
model_variable: Character string. The model_variable of the smoothing step to edit. Required when more than one smoothing step exists and step is not supplied.
step: Optional numeric index of the original smoothing step or one of its later edit steps. In both cases, the new edit is linked to the same original smoothing and appended after the existing workflow steps.
from, to: Optional numeric values giving the start and end of the source-variable interval to modify. For adjustment, either value may be omitted to use the beginning or end of the available smoothing range. For slope_adjustment, from is the required anchor and to must remain NULL. Explicit target-value and control-point edits require both values.
from_value, to_value: Optional numeric values used to override the smoothed curve value at from and to.
control_positions, control_values: Optional numeric vectors of equal length. These define additional points that the edited smoothing curve should pass through.
adjustment: Optional positive numeric scalar applied multiplicatively to the current smoothing within the selected interval. 1.05 requests an increase of up to 5 percent and 0.95 a decrease of up to 5 percent. With two boundaries, the default transition anchors the multiplier at 1 at from and to; a one-sided edit is anchored only at the supplied boundary.
slope_adjustment: Positive numeric scalar controlling the change in slope after from. The default 1 leaves the curve unchanged. Values above 1 strengthen the remaining change; values between 0 and 1 flatten it. This argument is available only in edit_smoothing().
transition: Optional character string controlling how adjustment connects to the unchanged smoothing. NULL inherits the original smoothing specification. "linear" gives continuous linear transitions and "step" permits immediate jumps. Smoothing methods accepted by add_smoothing() can be supplied as explicit structural overrides.
allow_extrapolation: Logical. Whether edits may extend beyond the observed source-variable range.
extrapolation_step: Optional positive numeric scalar used to set the spacing of extra break points when extrapolation is allowed.

Value

A rating_refinement object with a separate smoothing-edit step appended to the ordered specification. The pricing GLM is not fitted again until refit() is called.

Details

edit_smoothing() appends a separate, ordered edit step to a rating_refinement object. It does not alter the fitted GLM immediately. Repeated calls are cumulative: every new edit starts from the smoothing produced by preceding edits to the same add_smoothing() step. The selected cumulative curve is applied when refit() is called.

Use model_variable or step to identify the smoothing to edit. step may identify either its original add_smoothing() step or a later edit belonging to that smoothing. The interval from from to to defines the part of the source-variable range that should be changed. With adjustment, either boundary may be omitted. Supplying only from edits the curve from that value to the end of the smoothing range; supplying only to edits it from the beginning of the range to that value. adjustment multiplies the current smoothing within the selected range. For example, adjustment = 1.05 requests an increase of up to 5 percent relative to the existing smoothing.

With two boundaries, the multiplier is anchored at 1 at from and to and reaches the requested adjustment near the middle. With only from, it is anchored at 1 at from and moves towards the requested adjustment at the end of the range. With only to, it starts at the requested adjustment and reconnects to 1 at to. These one-sided forms are useful for refining a lower or upper tail without introducing a jump at the supplied boundary.

By default, transition = NULL inherits the smoothing specification from the add_smoothing() step. The entry and exit are adapted to their opposite directions and join the unchanged curve continuously. "linear" uses continuous straight transitions. "step" applies the multiplier immediately at both boundaries and therefore permits deliberate jumps. Explicit shape-constrained transition names accepted by add_smoothing() can also be supplied. When a constrained transition is inherited or selected, the edited curve is checked for the corresponding monotonicity and curvature.

from_value and to_value instead prescribe curve values at the interval boundaries. control_positions and control_values add points that the edited curve should follow inside the interval. Relative adjustments and explicit target values cannot be combined in one edit_smoothing() call because they represent different actuarial instructions. They may be used in separate consecutive edits, which are then evaluated in their stored order.

slope_adjustment changes the remaining increase or decrease after from, while keeping the curve before that point unchanged. If \(R(x)\) is the current smoothing and \(a\) is from, the edited curve is \(R(a) + s[R(x) - R(a)]\) for \(x > a\), where \(s\) is slope_adjustment. A value of 1.10 therefore makes the change after the anchor 10 percent stronger; 0.90 makes it 10 percent weaker. The curve is continuous at the anchor.

Each call applies one edit type: a relative adjustment, a slope_adjustment, or explicit target/control-point values. Apply multiple changes in consecutive calls so that every actuarial intervention remains a separate, inspectable refinement step.

Actuarial interpretation

The edited interval is an explicit tariff assumption layered on the statistically fitted smoothing curve. It should be supported by an actuarial rationale and reviewed against exposure, observed experience and the continuity of adjacent segments. The edit does not add information to sparse parts of the portfolio and should not be interpreted as a new model estimate.

Keep the rating_refinement object, call refit() to assess the current specification, edit that same refinement object, and call refit() again. The previously fitted GLM remains unchanged. This retains the order and content of manual adjustments as part of the reproducible refinement specification.

Author

Martin Haringa

Examples

set.seed(42)
driver_age <- rep(seq(20, 59), each = 4)
exposure <- rep(1, length(driver_age))
age_band <- cut(
  driver_age,
  breaks = c(18, 30, 40, 50, 60),
  include.lowest = TRUE
)
expected_claims <- exp(
  -1.7 + 0.018 * (driver_age - 20) + 0.0006 * (driver_age - 40)^2
)
portfolio <- data.frame(
  claims = rpois(length(driver_age), exposure * expected_claims),
  exposure = exposure,
  driver_age = driver_age,
  age_band = age_band
)

model <- glm(
  claims ~ age_band + offset(log(exposure)),
  family = poisson(),
  data = portfolio
)

refinement <- prepare_refinement(model, data = portfolio) |>
  add_smoothing(
    model_variable = "age_band",
    source_variable = "driver_age",
    breaks = c(18, 30, 40, 50, 60),
    weights = "exposure"
  )

# Fit and inspect the initial smoothing specification.
initial_model <- refit(refinement)

# Edit the retained specification and fit it again.
explicit_refinement <- refinement |>
  edit_smoothing(
    model_variable = "age_band",
    from = 30,
    to = 50,
    from_value = 1.00,
    to_value = 1.10,
    control_positions = c(40),
    control_values = c(1.05)
  )

explicit_model <- refit(explicit_refinement)

# Keep the current shape as the basis and raise the middle of this interval
# by up to 5 percent. The inherited transition remains continuous.
adjusted_refinement <- refinement |>
  edit_smoothing(
    model_variable = "age_band",
    from = 30,
    to = 50,
    adjustment = 1.05
  )

adjusted_model <- refit(adjusted_refinement)

# Keep the curve unchanged through age 40, then strengthen its remaining
# change by 10 percent while retaining continuity at age 40.
steeper_refinement <- refinement |>
  edit_smoothing(
    model_variable = "age_band",
    from = 40,
    slope_adjustment = 1.10
  )

# A one-sided adjustment applies from age 40 to the end of the range.
upper_tail_refinement <- refinement |>
  edit_smoothing(
    model_variable = "age_band",
    from = 40,
    adjustment = 1.05,
    transition = "linear"
  )