Description Usage Arguments Details Value Author(s) References Examples
View source: R/SurrogateOutcome.R
Calculates the proportion of the treatment effect (the difference in restriced mean survival time at time t) explained by surrogate outcome information observed up to the landmark time; also provides standard error estimate and confidence interval.
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xone |
numeric vector, observed event times for the primary outcome in the treatment group. |
xzero |
numeric vector, observed event times for the primary outcome in the control group. |
deltaone |
numeric vector, event/censoring indicators for the primary outcome in the treatment group. |
deltazero |
numeric vector, event/censoring indicators for the primary outcome in the control group. |
sone |
numeric vector, observed event times for the surrogate outcome in the treatment group. |
szero |
numeric vector, observed event times for the surrogate outcome in the control group. |
t |
time of interest for treatment effect. |
landmark |
landmark time of interest, t_0. |
number |
number of points for RMST calculation, default is 40. |
transform |
TRUE or FALSE; indicates whether a transformation should be used, default is FALSE. |
extrapolate |
TRUE or FALSE; indicates whether local constant extrapolation should be used, default is FALSE. |
std |
TRUE or FALSE; indicates whether standard error estimates should be provided, default is FALSE. Estimates are calculated using perturbation-resampling. Two versions are provided: one that takes the standard deviation of the perturbed estimates (denoted as "sd") and one that takes the median absolute deviation (denoted as "mad"). |
conf.int |
TRUE or FALSE; indicates whether 95% confidence intervals should be provided. Confidence intervals are calculated using the percentiles of perturbed estimates, default is FALSE. If this is TRUE, standard error estimates are automatically provided. |
weight.perturb |
weights used for perturbation resampling. |
type |
Type of estimate that should be provided; options are "np" for the nonparametric estimate or "semi" for the semiparametric estimate, default is "np". |
Let G \in \{1,0\} be the randomized treatment indicator, T denote the time of the primary outcome of interest, and S denote the time of the surrogate outcome. We use potential outcomes notation such that T^{(G)} and S^{(G)} denote the respective times of the primary and surrogate outcomes under treatment G, for G \in \{1, 0\}. In the absence of censoring, we only observe (T, S)=(T^{(1)}, S^{(1)}) or (T^{(0)}, S^{(0)}) for each individual depending on whether G=1 or 0. Due to censoring, data consist of n = n_1 + n_0 independent observations \{X_{gi}, δ_{gi}, I(S_{gi}< t_0)I(X_{gi} > t_0), S_{gi}\wedge t_0 I(X_{gi} > t_0), i=1,...,n_g, g = 1,0\}, where X_{gi} = T_{gi}\wedge C_{ gi}, δ_{gi} = I(T_{gi} < C_{gi}), C_{gi} denotes the censoring time, T_{gi} denotes the time of the primary outcome, S_{gi} denotes the time of the surrogate outcome, \{(T_{gi}, C_{gi}, S_{gi}), i = 1, ..., n_g\} are identically distributed within treatment group, and t_0 is the landmark time of interest.
We define the treatment effect as the difference in restricted mean survival time up to a fixed time t under treatment 1 versus under treatment 0,
Δ(t)=E\{T^{(1)}\wedge t\} - E\{T^{(0)}\wedge t \}
where \wedge indicates the minimum. To define the proportion of treatment effect explained by the surrogate outcome information, let
Q_{t_0} ^{(g)} = (Q_{t_01}, Q_{t_02})'=\{S ^{(g)} \wedge t_0I(T ^{(g)} > t_0), T^{(g)} I(T^{(g)} ≤ t_0)\}', g=1, 0
and define the residual treatment effect after accounting for the treatment effect on the surrogate outcome information as:
Δ_Q(t,t_0) = P ^{(0)}_{t_0,2}\int_0^{t_0} φ_1(t|t_0,s)dF_0(s) + P^{(0)}_{t_0,3}ψ_1(t|t_0) - P(T ^{(0)}> t_0) ν_0(t|t_0)
where P^{(0)}_{t_0,2} = P(T^{(0)} > {t_0}, S ^{(0)} < t_0) and P^{(0)}_{t_0,3} = P(T^{(0)} > {t_0}, S ^{(0)} > t_0), ψ_1(t \mid t_0) = E(T^{(1)}\wedge t \mid T^{(1)}> t_0, S^{(1)} > t_0), φ_1(t\mid t_0,s) = E(T^{(1)}\wedge t \mid T ^{(1)}> t_0, S ^{(1)} = s), \quad ν_0(t|t_0) = E(T ^{(0)} \wedge t | T ^{(0)}> t_0), and F_0(\cdot\mid t_0) is the cumulative distribution function of S^{(0)} conditional on T ^{(0)}> t_0 and S ^{(0)} < t_0. Then, the proportion of treatment effect on the primary outcome that is explained by surrogate information up to t_0, Q_{t_0}, can be expressed as a contrast between Δ(t) and Δ_Q(t,t_0):
R_Q(t,t_0) = \{Δ(t) - Δ_Q(t,t_0) \} / Δ(t) = 1- Δ_Q(t,t_0) / Δ(t).
The quantity Δ(t) is estimated using inverse probability of censoring weights:
\hat{Δ}(t) = n_1^{-1} ∑_{i=1}^{n_1} \hat{M}_{1i}(t)- n_0^{-1} ∑_{i=1}^{n_0} \hat{M}_{0i}(t)
where \hat{M}_{gi}(t) = I(X_{gi} > t)t/\hat{W}^C_g(t) + I(X_{gi} < t)X_{gi}δ_{gi}/\hat{W}^C_g(X_{gi}) and \hat{W}^C_g(t) is the Kaplan-Meier estimator of P(C_{gi} ≥ t). The residual treatment effect Δ_Q(t,t_0) can be estimated nonparametrically or semi-parametrically. For nonparametric estimation, ψ_{1}(t|t_0) is estimated by \hat{ψ}_{1}(t|t_0) = ∑_{i=1}^{n_1}\frac{ { \hat{W}^C_1(t_0)} I(S_{1i}>t_0, X_{1i} > t_0) }{ ∑_{i=1}^{n_1}I(S_{1i}>t_0, X_{1i} > t_0)} \hat{M}_{1i}(t), and φ_1(t \mid t_0,s) = E(T^{(1)}\wedge t\mid X^{(1)}> t_0, S ^{(1)} = s) is estimated using a nonparametric kernel Nelson-Aalen estimator for Λ_1(t\mid t_0,s ), the cumulative hazard function of T^{(1)} conditional on S^{(1)}=s and T^{(1)}>t_0, as
\hat φ_1(t \mid t_0,s) = t_0+\int_ {t_0}^t \exp\{-\hat{Λ}_1(t\mid t_0,s) \}dt,
where
\hat{Λ}_1(t\mid t_0,s) = \int_{t_0}^t \frac{∑_{i=1}^{n_1} I(X_{1i}>t_0, {S_{1i} < t_0}) K_h\{γ(S_{1i}) - γ(s)\}dN_{1i}(z)}{∑_{i=1}^{n_1} I(X_{1i}>t_0, {S_{1i} < t_0}) K_h\{γ(S_{1i}) - γ(s)\} Y_{1i}(z)},
is a consistent estimate of Λ_1(t\mid t_0,s ), Y_{1i}(t) = I(X_{1i} ≥q t), N_{1i}(t) = I(X_{1i} ≤q t) δ_i, K(\cdot) is a smooth symmetric density function, K_h(x) = K(x/h)/h, γ(\cdot) is a given monotone transformation function, and h=O(n_1^{-η}) is a specified bandwidth with η \in (1/2,1/4). Finally, we let
\hat{ν}_{0}(t|t_0) = ∑_{i=1}^{n_0}\frac{ {\hat{W}^C_0(t_0)}I(X_{0i} > t_0) }{ ∑_{i=1}^{n_0}I(X_{0i} > t_0)} \hat{M}_{0i}(t).
We then estimate Δ_{Q}(t,t_0) as \hat{Δ}_{Q}(t,t_0) defined as
n_0^{-1} ∑_{i=1}^{n_0} ≤ft \{ \frac{I_{t_0,2}(X_{0i}, S_{0i})\hat{φ}_1(t\mid t_0, S_{0i}) + I_{t_0,3}(X_{0i}, S_{0i})\hat{ψ}_1(t\mid t_0) - I_{t_0}(X_{0i})\hat{ν}(t|t_0) }{\hat{W}^C_0(t_0)} \right \}
where I_{t_0,2}(x, s) = I(x > {t_0}, s < t_0) and I_{t_0,3}(x, s) = I(x > {t_0}, s > t_0) and I_{t_0}(x)=I(x > {t_0}) and thus, \hat{R}_Q(t,t_0) =1- \hat{Δ}_Q(t,t_0)/\hat{Δ}(t).
For the semi-parametric estimate, \hat φ_1(t| t_0,s) is replaced with an estimate obtained using a landmark Cox proportional hazards model
P(T^{(1)}> t\mid T^{(1)}> t_0, S^{(1)} < t_0, S ^{(1)}) = \exp \{ -Λ_0(t|t_0)\exp(β_0S ^{(1)})\}
where Λ_0(t|t_0) is the unspecified baseline cumulative hazard among Ω_{t_0} = \{T^{(1)}> t_0, S^{(1)} < t_0\} and β_0 is unknown. That is, let \tilde φ_1(t| t_0,s) = t_0+\int_{t_0}^{t}\exp \{ -\hat{Λ}_0(t|t_0)\exp(\hat{β}s)\} dt, where \hat{β} is estimated by fitting a Cox model to the subpopulation Ω_{t_0} with a single predictor S and \hat{Λ}_0(\cdot|t_0) is the corresponding Breslow estimator. Then the semiparametric estimator for Δ_{Q}(t,t_0) is \tilde{Δ}_{Q}(t,t_0) defined as
n_0^{-1} ∑_{i=1}^{n_0} ≤ft \{ \frac{I_{t_0,2}(X_{0i}, S_{0i})\tilde{φ}_1(t\mid t_0, S_{0i}) + I_{t_0,3}(X_{0i}, S_{0i})\hat{ψ}_1(t\mid t_0) - I_{t_0}(X_{0i})\hat{ν}(t|t_0) }{\hat{W}^C_0(t_0)} \right \}
and \tilde{R}_Q(t,t_0) =1- \tilde{Δ}_Q(t,t_0)/\hat{Δ}(t).
A list is returned:
delta |
the estimate, \hat{Δ}(t), described in delta.estimate documentation. |
delta.q |
the estimate, \hat{Δ}_Q(t,t_0), described above. |
R.q |
the estimate, \hat{R}_Q(t,t_0), described above. |
delta.sd |
the standard error estimate of \hat{Δ}(t); if std = TRUE or conf.int = TRUE. |
delta.mad |
the standard error estimate of \hat{Δ}(t) using the median absolute deviation; if std = TRUE or conf.int = TRUE. |
delta.q.sd |
the standard error estimate of \hat{Δ}_Q(t,t_0); if std = TRUE or conf.int = TRUE. |
delta.q.mad |
the standard error estimate of \hat{Δ}_Q(t,t_0) using the median absolute deviation; if std = TRUE or conf.int = TRUE. |
R.q.sd |
the standard error estimate of \hat{R}_Q(t,t_0); if std = TRUE or conf.int = TRUE. |
R.q.mad |
the standard error estimate of \hat{R}_Q(t,t_0) using the median absolute deviation; if std = TRUE or conf.int = TRUE. |
conf.int.delta |
a vector of size 2; the 95% confidence interval for \hat{Δ}(t) based on sample quantiles of the perturbed values; if conf.int = TRUE. |
conf.int.delta.q |
a vector of size 2; the 95% confidence interval for \hat{Δ}_Q(t,t_0) based on sample quantiles of the perturbed values; if conf.int = TRUE. |
conf.int.R.q |
a vector of size 2; the 95% confidence interval for \hat{R}_Q(t,t_0) based on sample quantiles of the perturbed values; if conf.int = TRUE. |
Layla Parast
Parast L, Tian L, and Cai T (2020). Assessing the Value of a Censored Surrogate Outcome. Lifetime Data Analysis, 26(2):245-265.
Parast, L and Cai, T (2013). Landmark risk prediction of residual life for breast cancer survival. Statistics in Medicine, 32(20), 3459-3471.
1 2 3 4 5 6 7 8 9 10 11 12 13 | data(ExampleData)
names(ExampleData)
R.q.event(xone = ExampleData$x1, xzero = ExampleData$x0, deltaone = ExampleData$delta1,
deltazero = ExampleData$delta0, sone = ExampleData$s1, szero = ExampleData$s0, t = 5,
landmark=2, type = "np")
R.q.event(xone = ExampleData$x1, xzero = ExampleData$x0, deltaone = ExampleData$delta1,
deltazero = ExampleData$delta0, sone = ExampleData$s1, szero = ExampleData$s0, t = 5,
landmark=2, type = "semi")
R.q.event(xone = ExampleData$x1, xzero = ExampleData$x0, deltaone = ExampleData$delta1,
deltazero = ExampleData$delta0, sone = ExampleData$s1, szero = ExampleData$s0, t = 5,
landmark=2, type = "np", std = TRUE, conf.int = TRUE)
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