gorica: Evaluate informative hypotheses using the GORICA

Description Usage Arguments Details Value Author(s) References Examples

View source: R/gorica_methods.R

Description

GORICA is an acronym for "generalized order-restricted information criterion approximation". It can be utilized to evaluate informative hypotheses, which specify directional relationships between model parameters in terms of (in)equality constraints.

Usage

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gorica(x, hypothesis, comparison = "unconstrained", ...)

Arguments

x

An R object containing the outcome of a statistical analysis. Currently, the following objects can be processed:

  • lm() objects (anova, ancova, multiple regression).

  • t_test() objects.

  • lavaan objects.

  • lmerMod objects.

  • A named vector containing the estimates resulting from a statistical analysis, when the argument Sigma is also specified. Note that, named means that each estimate has to be labeled such that it can be referred to in hypotheses.

hypothesis

A character string containing the informative hypotheses to evaluate (see Details).

comparison

A character string indicating what the hypothesis should be compared to. Defaults to comparison = "unconstrained"; options include c("unconstrained", "complement", "none").

...

Additional arguments passed to the internal function compare_hypotheses.

Details

The GORICA is applicable to not only normal linear models, but also applicable to generalized linear models (GLMs) (McCullagh & Nelder, 1989), generalized linear mixed models (GLMMs) (McCullogh & Searle, 2001), and structural equation models (SEMs) (Bollen, 1989). In addition, the GORICA can be utilized in the context of contingency tables for which (in)equality constrained hypotheses do not necessarily contain linear restrictions on cell probabilities, but instead often contain non-linear restrictions on cell probabilities.

hypotheses is a character string that specifies which informative hypotheses have to be evaluated. A simple example is hypotheses <- "a > b > c; a = b = c;" which specifies two hypotheses using three estimates with names "a", "b", and "c", respectively.

The hypotheses specified have to adhere to the following rules:

  1. Parameters are referred to using the names specified in names().

  2. Linear combinations of parameters must be specified adhering to the following rules:

    1. Each parameter name is used at most once.

    2. Each parameter name may or may not be pre-multiplied with a number.

    3. A constant may be added or subtracted from each parameter name.

    4. A linear combination can also be a single number.

    Examples are: 3 * a + 5; a + 2 * b + 3 * c - 2; a - b; and 5.

  3. (Linear combinations of) parameters can be constrained using <, >, and =. For example, a > 0 or a > b = 0 or 2 * a < b + c > 5.

  4. The ampersand & can be used to combine different parts of a hypothesis. For example, a > b & b > c which is equivalent to a > b > c or a > 0 & b > 0 & c > 0.

  5. Sets of (linear combinations of) parameters subjected to the same constraints can be specified using (). For example, a > (b,c) which is equivalent to a > b & a > c.

  6. The specification of a hypothesis is completed by typing ; For example, hypotheses <- "a > b > c; a = b = c;", specifies two hypotheses.

  7. Hypotheses have to be compatible, non-redundant and possible. What these terms mean will be elaborated below.

The set of hypotheses has to be compatible. For the statistical background of this requirement see Gu, Mulder, Hoijtink (2018). Usually the sets of hypotheses specified by researchers are compatible, and if not, gorica will return an error message. The following steps can be used to determine if a set of hypotheses is compatible:

  1. Replace a range constraint, e.g., 1 < a1 < 3, by an equality constraint in which the parameter involved is equated to the midpoint of the range, that is, a1 = 2.

  2. Replace in each hypothesis the < and > by =. For example, a1 = a2 > a3 > a4 becomes a1 = a2 = a3 = a4.

  3. The hypotheses are compatible if there is at least one solution to the resulting set of equations. For the two hypotheses considered under 1. and 2., the solution is a1 = a2 = a3 = a4 = 2. An example of two non-compatible hypotheses is hypotheses <- "a = 0; a > 2;" because there is no solution to the equations a=0 and a=2.

Each hypothesis in a set of hypotheses has to be non-redundant. A hypothesis is redundant if it can also be specified with fewer constraints. For example, a = b & a > 0 & b > 0 is redundant because it can also be specified as a = b & a > 0. gorica will work correctly if hypotheses specified using only < and > are redundant. gorica will return an error message if hypotheses specified using at least one = are redundant.

Each hypothesis in a set of hypotheses has to be possible. An hypothesis is impossible if estimates in agreement with the hypothesis do not exist. For example: values for a in agreement with a = 0 & a > 2 do not exist. It is the responsibility of the user to ensure that the hypotheses specified are possible. If not, gorica will either return an error message or render an output table containing Inf's.

Value

An object of class gorica, containing the following elements:

Author(s)

Caspar van Lissa, Yasin Altinisik, Rebecca Kuiper

References

Altinisik, Y. (2018). Evaluation of Inequality Constrained Hypotheses Using an Akaike-Type Information Criterion (Doctoral dissertation, Utrecht University). ISBN: 978-90-393-6918-0. https://dspace.library.uu.nl/handle/1874/360604

Bollen, K. (1989). Structural equations with latent variables. New York, NY: John Wiley and Sons.

Kuiper, R. M., Hoijtink, H., & Silvapulle, M. J. (2011). An Akaike-type information criterion for model selection under inequality constraints. Biometrika, 98, 495-501. doi:10.1093/biomet/asr002

Kuiper, R. M., Hoijtink, H., & Silvapulle, M. J. (2012). Generalization of the order-restricted information criterion for multivariate normal linear models. Journal of statistical planning and inference, 142(8), 2454-2463. doi:10.1016/j.jspi.2012.03.007

McCullagh, P. & Nelder, J. (1989). Generalized linear models (2nd ed.). Boca Raton, FL: Chapman & Hall / CRC.

McCullogh, C. E., & Searle, S. R. (2001). Generalized linear and mixed models. New York, NY: Wiley.

Examples

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# EXAMPLE 1. One-sample t test
ttest1 <- t_test(iris$Sepal.Length,mu=5)
gorica(ttest1,"x<5.8")

# EXAMPLE 2. ANOVA
aov1 <- aov(yield ~ block-1 + N * P + K, npk)
gorica(aov1,hypothesis="block1=block5;
   K1<0")

# EXAMPLE 3. gml
counts <- c(18,17,15,20,10,20,25,13,12)
outcome <- gl(3,1,9)
treatment <- gl(3,3)
fit <- glm(counts ~ outcome-1 + treatment, family = poisson())
gorica(fit, "outcome1 > (outcome2, outcome3)")

# EXAMPLE 4. ANOVA
res <- lm(Sepal.Length ~ Species-1, iris)
est <- get_estimates(res)
est
gor <- gorica(res, "Speciessetosa < (Speciesversicolor, Speciesvirginica)",
comparison = "complement")
gor

gorica documentation built on Jan. 9, 2020, 1:12 a.m.