The theory and application of statistical quality control is well establish
ed in precise positioning, navigation and geodesy. Quality control is made
up of several contributing factors, one of which is internal reliability. I
nternal reliability describes the ability to find biases in observational d
ata and is represented by the Minimal Detectable Bias (MDB). The MDB provid
es a diagnostic tool to infer the strength with which positioning models ca
n be validated. In this contribution closed-form expressions will be given
for the MDBs of GPS code and carrier observations for three different basel
ine models: the geometry-free model and two variants of the geometry-based
model. These expressions apply to any number of carrier frequencies. The ex
pressions take into account the presence of ionospheric disturbances by wei
ghting these effects. As such, they are applicable to baselines of any leng
th.