est_ce {vaccine}

Estimate controlled effect curves

Description

Estimate controlled risk (CR) curves and/or controlled vaccine efficacy (CVE) curves. See references for definitions of these curves.

Usage

est_ce(
  dat,
  type = "Cox",
  t_0,
  cr = TRUE,
  cve = FALSE,
  s_out = seq(from = min(dat$s, na.rm = TRUE), to = max(dat$s, na.rm = TRUE), l = 101),
  ci_type = "transformed",
  placebo_risk_method = "KM",
  return_p_value = FALSE,
  return_extras = FALSE,
  params_cox = params_ce_cox(),
  params_np = params_ce_np()
)

Arguments

dat

A data object returned by load_data

type

One of c("Cox", "NP"). This specifies whether to estimate the curve(s) using a marginalized Cox proportional hazards model or using a monotone-constrained nonparametric estimator.

t_0

Time point of interest

cr

Boolean. If TRUE, the controlled risk (CR) curve is computed and returned.

cve

Boolean. If TRUE, the controlled vaccine efficacy (CVE) curve is computed and returned.

s_out

A numeric vector of s-values (on the biomarker scale) for which cve(s) and/or cr(s) are computed. Defaults to a grid of 101 points between the min and max biomarker values.

ci_type

One of c("transformed", "truncated", "regular", "none"). If ci_type="transformed", confidence intervals are computed on the logit(CR) and/or log(1-CVE) scale to ensure that confidence limits lie within [0,1] for CR and/or lie within (-inf,1] for CVE. If ci_type="truncated", confidence limits are constructed on the CR and/or CVE scale but truncated to lie within [0,1] for CR and/or lie within (-inf,1] for CVE. If ci_type="regular", confidence limits are not transformed or truncated. If ci_type="none", confidence intervals are not computed.

placebo_risk_method

One of c("KM", "Cox"). Method for estimating overall risk in the placebo group. "KM" computes a Kaplan-Meier estimate and "Cox" computes an estimate based on a marginalized Cox model survival curve. Only relevant if cve=TRUE.

return_p_value

Boolean; if TRUE, a P-value corresponding to the null hypothesis that the CVE curve is flat is returned. The type of P-value corresponds to the type argument.

return_extras

Boolean; if TRUE, objects useful for debugging are returned.

params_cox

A list of options returned by params_ce_cox that are relevant if type="Cox".

params_np

A list of options returned by params_ce_np that are relevant if type="NP".

Value

A list of the form list(cr=list(...), cve=list(...)) containing CR and/or CVE estimates. Each of the inner lists contains the following:

• s: a vector of marker values corresponding to s_out

• est: a vector of point estimates

• ci_lower: a vector of confidence interval lower limits

• ci_upper: a vector of confidence interval upper limits

References

Gilbert P, Fong Y, Kenny A, and Carone, M (2022). A Controlled Effects Approach to Assessing Immune Correlates of Protection. <doi:10.1093/biostatistics/kxac024>

Examples

data(hvtn505)
dat <- load_data(time="HIVwk28preunblfu", event="HIVwk28preunbl", vacc="trt",
                 marker="IgG_V2", covariates=c("age","BMI","bhvrisk"),
                 weights="wt", ph2="casecontrol", data=hvtn505)

ests_cox <- est_ce(dat=dat, type="Cox", t_0=578)
ests_np <- est_ce(dat=dat, type="NP", t_0=578)