Computes confidence intervals for cumulative count estimates using the influence curve or supplied bootstrap replicates to estimate standard errors.

compute_cumcount_effect_ci(
  obj,
  alpha = 0.05,
  ic = FALSE,
  count_time = NULL,
  ref = 1,
  effect_measure_type = "CD",
  boot_method = "normal"
)

Arguments

obj

A cumcount object containing the count estimates, e.g., as computed by estimate_ipwcount

alpha

The desired nominal significance level of the confidence intervals.

ic

If the supplied object contains a bootstrap count estimates, setting ic = TRUE will requests that estimated standard errors be derived from the influence curve.

count_time

The time at which the cumulative count estimates should be returned (the default value NULL returns all times)

ref

The category to use as the reference for count difference calculations.

effect_measure_type

A string identifying the type of effect measure to be computed from among the following options: "CD" (count difference) or "CR" (count ratio). Note that when obj was created using bootstrap estimation and boot_method is "log-normal", then only effect measures with support on the positive real line can be used (i.e. "CR"). See the Effect measure types section for the definitions of the various effect measures.

boot_method

The specific bootstrap approach used to compute confidence intervals (default method = "normal" for a normal approximation on the risk scale, other choices include "log-normal" for normal approximation on the log scale). When obj was created without using bootstrap estimation then the value of boot_method is ignored. Note that when obj was created using bootstrap estimation and boot_method is "log-normal", then only effect measures specified via effect_measure_type with support on the positive real line can be used.

Value

A matrix containing the cumulative count and confidence interval for each time point and treatment group.

Cumulative count effect measure types

Count difference

Mean: \(\mathrm{E}[Y^{1}] - \mathrm{E}[Y^{0}]\)

Variance with IPW: \( \mathrm{Var}[Y^{1}] + \mathrm{Var}[Y^{0}] + \frac{2}{n} \mathrm{E}[Y^{1}] \, \mathrm{E}[Y^{0}] \)

Variance otherwise: \(\mathrm{Var}[Y^{1}] + \mathrm{Var}[Y^{0}]\)

Count ratio

Mean: \(\frac{\mathrm{E}[Y^{1}]}{\mathrm{E}[Y^{0}]}\)

Variance with IPW: \( \frac{\mathrm{Var}[Y^{1}]}{(\mathrm{E}[Y^{0}])^{2}} + \frac{\mathrm{Var}[Y^{0}]\,(\mathrm{E}[Y^{1}])^2} {(\mathrm{E}[Y^{0}])^{4}} + \frac{2\,(\mathrm{E}[Y^{1}])^2}{n\,(\mathrm{E}[Y^{0}])^2} \)

Variance otherwise: \( \frac{\mathrm{Var}[Y^{1}]}{(\mathrm{E}[Y^{0}])^{2}} + \frac{\mathrm{Var}[Y^{0}]\,(\mathrm{E}[Y^{1}])^2} {(\mathrm{E}[Y^{0}])^{4}} \)

Author

M. Alan Brookhart & Alexander Breskin