Define relationship between parameters and covariates
The Expression
property is a string or cell
array of strings, where each string represents the relationship between
a parameter and one or more covariates. The Expression
property
denotes fixed effects with the prefix theta
, and
random effects with the prefix eta
.
Each expression string must be in the form:
parameterName = relationship |
This example of an expression string defines the relationship
between a parameter (volume
) and a covariate (weight
),
with fixed effects, but no random effects:
CovModelObj.Expression = {'volume = theta1 + theta2*weight'}; |
This table illustrates expression formats for some common parameter-covariate relationships.
Parameter-Covariate Relationship | Expression Format |
---|---|
Linear with random effect | Cl = theta1 + theta2*WEIGHT + eta1 |
Exponential without random effect | Cl = exp(theta_Cl + theta_Cl_WT*WEIGHT) |
Exponential, WEIGHT centered by mean, has random effect | Cl = exp(theta1 + theta2*(WEIGHT - mean(WEIGHT)) +
eta1) |
Exponential, log(WEIGHT), which is equivalent to power model | Cl = exp(theta1 + theta2*log(WEIGHT) + eta1) |
Exponential, dependent on WEIGHT and AGE, has random effect | Cl = exp(theta1 + theta2*WEIGHT + theta3*AGE + eta1) |
Inverse of probit, dependent on WEIGHT and AGE, has random effect | Cl = probitinv(theta1 + theta2*WEIGHT + theta3*AGE
+ eta1) |
Inverse of logit, dependent on WEIGHT and AGE, has random effect | Cl = logitinv(theta1 + theta2*WEIGHT + theta3*AGE
+ eta1) |
Tip
To simultaneously fit data from multiple dose levels, use a |
The Expression
property must meet the following
requirements:
The expression strings are valid MATLAB^{®} code.
Each expression string is linear with a transformation.
There is exactly one expression string for each parameter.
In each expression string, a covariate is used in at most one term.
In each expression string, there is at most one random
effect (eta
)
Fixed effect (theta
) and random
effect (eta
) names are unique within and across
expression strings. That is, each covariate has its own fixed effect.
Tip
Use the |
Tip
Use the |
Applies to | Object: CovariateModel |
Data type | String or cell array of strings |
Data values | parameterName = relationship |
Access | Read/write |