csranks: Confidence sets for ranks

In danielwilhelm/R-CS-ranks: Statistical Tools for Ranks

Confidence sets for ranks

Description

Marginal and simultaneous confidence sets for ranks.

Usage

csranks(
  x,
  Sigma,
  coverage = 0.95,
  cstype = "two-sided",
  stepdown = TRUE,
  R = 1000,
  simul = TRUE,
  indices = NA,
  na.rm = FALSE,
  seed = NA
)

Arguments

x	vector of estimates containing estimated features by which the populations are to be ranked.
Sigma	estimated covariance matrix of x.
coverage	nominal coverage of the confidence set. Default is 0.95.
cstype	type of confidence set (two-sided, upper, lower). Default is two-sided.
stepdown	logical; if TRUE (default), stepwise procedure is used, otherwise single step procedure is used. See Details section for more.
R	number of bootstrap replications. Default is 1000.
simul	logical; if TRUE (default), then simultaneous confidence sets are computed, which jointly cover all populations indicated by indices. Otherwise, for each population indicated in indices a marginal confidence set is computed.
indices	vector of indices of x for whose ranks the confidence sets are computed. indices=NA (default) means computation of confidence sets for all populations.
na.rm	logical; if TRUE, then NA's are removed from x and Sigma (if any).
seed	seed for bootstrap random variable draws. If set to NA (default), then seed is not set.

Value

A csranks object, which is a list with three items:

L

Lower bounds of the confidence sets for ranks indicated in indices

rank

Estimated ranks from irank with default parameters

U

Upper bounds of the confidence sets.

Details

Suppose j=1,\ldots,p populations (e.g., schools, hospitals, political parties, countries) are to be ranked according to some measure \theta=(\theta_1,\ldots,\theta_p). We do not observe the true values \theta_1,\ldots,\theta_p. Instead, for each population, we have data from which we have estimated these measures, \hat{\theta}=(\hat{\theta}_1,\ldots,\hat{\theta}_p). The values \hat{\theta}_1,\ldots,\hat{\theta}_p are estimates of the true values \theta_1,\ldots,\theta_p and thus contain statistical uncertainty. In consequence, a ranking of the populations by the values \hat{\theta}_1,\ldots,\hat{\theta}_p contains statistical uncertainty and is not necessarily equal to the true ranking of \theta_1,\ldots,\theta_p.

The function computes confidence sets for the rank of one, several or all of the populations (indices indicates which of the 1,\ldots,p populations are of interest). x is a vector containing the estimates \hat{\theta}_1,\ldots,\hat{\theta}_p and Sigma is an estimate of the covariance matrix of x. The method assumes that the estimates are asymptotically normal and the sample sizes of the datasets are large enough so that \hat{\theta}-\theta is approximately distributed as N(0,\Sigma). The argument Sigma should contain an estimate of the covariance matrix \Sigma. For instance, if for each population j

\sqrt{n_j} (\hat{\theta}_j-\theta_j) \to_d N(0, \sigma_j^2)

and the datasets for each population are drawn independently of each other, then Sigma is a diagonal matrix

diag(\hat{\sigma}_1^2/n_1,\ldots,\hat{\sigma}_p^2/n_p)

containing estimates of the asymptotic variances divided by the sample size. More generally, the estimates in x may be dependent, but then Sigma must be an estimate of its covariance matrix including off-diagonal terms.

Marginal confidence sets (simul=FALSE) are such that the confidence set for a population j contains the true rank of that population j with probability approximately equal to the nominal coverage level. Simultaneous confidence sets (simul=TRUE) on the other hand are such that the confidence sets for populations indicated in indices cover the true ranks of all of these populations simultaneously with probability approximately equal to the nominal coverage level. For instance, in the PISA example below, a marginal confidence set of a country j covers the true rank of country j with probability approximately equal to 0.95. A simultaneous confidence set for all countries covers the true ranks of all countries simultaneously with probability approximately equal to 0.95.

The function implements the procedures developed and described in more detail in Mogstad, Romano, Shaikh, and Wilhelm (2023). The procedure is based on on testing a large family of hypotheses for pairwise comparisons. Stepwise methods can be used to improve the power of the procedure by, potentially, rejecting more hypotheses without violating the desired coverage property of the resulting confidence set. These are employed when stepdown=TRUE. From a practical point of view, stepdown=TRUE is computationally more demanding, but often results in tighter confidence sets.

The procedure uses a parametric bootstrap procedure based on the above approximate multivariate normal distribution.

References

Mogstad, Romano, Shaikh, and Wilhelm (2023), "Inference for Ranks with Applications to Mobility across Neighborhoods and Academic Achievements across Countries", forthcoming at Review of Economic Studies cemmap working paper \Sexpr[results=rd]{tools:::Rd_expr_doi("10.1093/restud/rdad006")}

Examples

# simple simulated example:
n <- 100
p <- 10
X <- matrix(rep(1:p,n)/p, ncol=p, byrow=TRUE) + matrix(rnorm(n*p), 100, 10)
thetahat <- colMeans(X)
Sigmahat <- cov(X) / n
csranks(thetahat, Sigmahat)

# PISA example:
data(pisa2018)
math_score <- pisa2018$math_score
math_se <- pisa2018$math_se
math_cov_mat <- diag(math_se^2)

# marginal confidence set for each country:
csranks(math_score, math_cov_mat, simul=FALSE)

# simultaneous confidence set for all countries:
csranks(math_score, math_cov_mat, simul=TRUE)

danielwilhelm/R-CS-ranks documentation built on Sept. 11, 2024, 4:18 p.m.