cTMed (version 1.0.5)

DeltaBeta: Delta Method Sampling Variance-Covariance Matrix for the Elements of the Matrix of Lagged Coefficients Over a Specific Time Interval or a Range of Time Intervals

Description

This function computes the delta method sampling variance-covariance matrix for the elements of the matrix of lagged coefficients $\mathit{\beta }$ over a specific time interval $\mathrm{\Delta }t$ or a range of time intervals using the first-order stochastic differential equation model's drift matrix $\mathbf{\Phi }$.

Usage

DeltaBeta(phi, vcov_phi_vec, delta_t, ncores = NULL, tol = 0.01)

Value

Returns an object of class ctmeddelta which is a list with the following elements:

call

Function call.

args

Function arguments.

fun

Function used ("DeltaBeta").

output

A list the length of which is equal to the length of delta_t.

Each element in the output list has the following elements:

delta_t

Time interval.

jacobian

Jacobian matrix.

est

Estimated elements of the matrix of lagged coefficients.

vcov

Sampling variance-covariance matrix of estimated elements of the matrix of lagged coefficients.

Arguments

phi

Numeric matrix. The drift matrix ($\mathbf{\Phi }$). phi should have row and column names pertaining to the variables in the system.

vcov_phi_vec

Numeric matrix. The sampling variance-covariance matrix of $\mathrm{vec}\left(\mathbf{\Phi }\right)$.

delta_t

Vector of positive numbers. Time interval ($\mathrm{\Delta }t$).

ncores

Positive integer. Number of cores to use. If ncores = NULL, use a single core. Consider using multiple cores when the length of delta_t is long.

tol

Numeric. Smallest possible time interval to allow.

Author

Ivan Jacob Agaloos Pesigan

Details

See Total().

Delta Method

Let $\mathit{\theta }$ be $\mathrm{vec}\left(\mathbf{\Phi }\right)$, that is, the elements of the $\mathbf{\Phi }$ matrix in vector form sorted column-wise. Let $\hat{\mathit{\theta }}$ be $\mathrm{vec}\left(\hat{\mathbf{\Phi }}\right)$. By the multivariate central limit theory, the function $\mathbf{g}$ using $\hat{\mathit{\theta }}$ as input can be expressed as:

$$\sqrt{n}(\mathbf{g}\left(\hat{\mathit{\theta }}\right)-\mathbf{g}\left(\mathit{\theta }\right))\stackrel{\mathrm{D}}{\to }\mathcal{N}(0,\mathbf{J}\mathbf{\Gamma }{\mathbf{J}}^{\prime })$$

where $\mathbf{J}$ is the matrix of first-order derivatives of the function $\mathbf{g}$ with respect to the elements of $\mathit{\theta }$ and $\mathbf{\Gamma }$ is the asymptotic variance-covariance matrix of $\hat{\mathit{\theta }}$.

From the former, we can derive the distribution of $\mathbf{g}\left(\hat{\mathit{\theta }}\right)$ as follows:

$$\mathbf{g}\left(\hat{\mathit{\theta }}\right)\approx \mathcal{N}(\mathbf{g}\left(\mathit{\theta }\right),n^{-1}\mathbf{J}\mathbf{\Gamma }{\mathbf{J}}^{\prime })$$

The uncertainty associated with the estimator $\mathbf{g}\left(\hat{\mathit{\theta }}\right)$ is, therefore, given by $n^{-1}\mathbf{J}\mathbf{\Gamma }{\mathbf{J}}^{\prime }$ . When $\mathbf{\Gamma }$ is unknown, by substitution, we can use the estimated sampling variance-covariance matrix of $\hat{\mathit{\theta }}$, that is, $\hat{\mathbb{V}}\left(\hat{\mathit{\theta }}\right)$ for $n^{-1}\mathbf{\Gamma }$. Therefore, the sampling variance-covariance matrix of $\mathbf{g}\left(\hat{\mathit{\theta }}\right)$ is given by

$$\mathbf{g}\left(\hat{\mathit{\theta }}\right)\approx \mathcal{N}(\mathbf{g}\left(\mathit{\theta }\right),\mathbf{J}\hat{\mathbb{V}}\left(\hat{\mathit{\theta }}\right){\mathbf{J}}^{\prime }).$$

References

Bollen, K. A. (1987). Total, direct, and indirect effects in structural equation models. Sociological Methodology, 17, 37. tools:::Rd_expr_doi("10.2307/271028")

Deboeck, P. R., & Preacher, K. J. (2015). No need to be discrete: A method for continuous time mediation analysis. Structural Equation Modeling: A Multidisciplinary Journal, 23 (1), 61–75. tools:::Rd_expr_doi("10.1080/10705511.2014.973960")

Ryan, O., & Hamaker, E. L. (2021). Time to intervene: A continuous-time approach to network analysis and centrality. Psychometrika, 87 (1), 214–252. tools:::Rd_expr_doi("10.1007/s11336-021-09767-0")

See Also

Other Continuous Time Mediation Functions: BootBeta(), BootBetaStd(), BootIndirectCentral(), BootMed(), BootMedStd(), BootTotalCentral(), DeltaBetaStd(), DeltaIndirectCentral(), DeltaMed(), DeltaMedStd(), DeltaTotalCentral(), Direct(), DirectStd(), ExpCov(), ExpMean(), Indirect(), IndirectCentral(), IndirectStd(), MCBeta(), MCBetaStd(), MCIndirectCentral(), MCMed(), MCMedStd(), MCPhi(), MCPhiSigma(), MCTotalCentral(), Med(), MedStd(), PosteriorBeta(), PosteriorIndirectCentral(), PosteriorMed(), PosteriorTotalCentral(), Total(), TotalCentral(), TotalStd(), Trajectory()

Examples

phi <- matrix(
  data = c(
    -0.357, 0.771, -0.450,
    0.0, -0.511, 0.729,
    0, 0, -0.693
  ),
  nrow = 3
)
colnames(phi) <- rownames(phi) <- c("x", "m", "y")
vcov_phi_vec <- matrix(
  data = c(
    0.00843, 0.00040, -0.00151,
    -0.00600, -0.00033, 0.00110,
    0.00324, 0.00020, -0.00061,
    0.00040, 0.00374, 0.00016,
    -0.00022, -0.00273, -0.00016,
    0.00009, 0.00150, 0.00012,
    -0.00151, 0.00016, 0.00389,
    0.00103, -0.00007, -0.00283,
    -0.00050, 0.00000, 0.00156,
    -0.00600, -0.00022, 0.00103,
    0.00644, 0.00031, -0.00119,
    -0.00374, -0.00021, 0.00070,
    -0.00033, -0.00273, -0.00007,
    0.00031, 0.00287, 0.00013,
    -0.00014, -0.00170, -0.00012,
    0.00110, -0.00016, -0.00283,
    -0.00119, 0.00013, 0.00297,
    0.00063, -0.00004, -0.00177,
    0.00324, 0.00009, -0.00050,
    -0.00374, -0.00014, 0.00063,
    0.00495, 0.00024, -0.00093,
    0.00020, 0.00150, 0.00000,
    -0.00021, -0.00170, -0.00004,
    0.00024, 0.00214, 0.00012,
    -0.00061, 0.00012, 0.00156,
    0.00070, -0.00012, -0.00177,
    -0.00093, 0.00012, 0.00223
  ),
  nrow = 9
)

# Specific time interval ----------------------------------------------------
DeltaBeta(
  phi = phi,
  vcov_phi_vec = vcov_phi_vec,
  delta_t = 1
)

# Range of time intervals ---------------------------------------------------
delta <- DeltaBeta(
  phi = phi,
  vcov_phi_vec = vcov_phi_vec,
  delta_t = 1:5
)
plot(delta)

# Methods -------------------------------------------------------------------
# DeltaBeta has a number of methods including
# print, summary, confint, and plot
print(delta)
summary(delta)
confint(delta, level = 0.95)
plot(delta)