"poor approximation" is correct and usable in written English.
You can use it when you want to describe something that is not an exact result, but one that is close enough. For example, "His estimation of the cost of the project was a poor approximation, but it gave us a starting point for further investigation."
"We're not the freak of the universe — but we are a very poor approximation," Kipping says.
Relying on asymptotics in these cases might result in poor approximation and consequently faulty conclusions.
And put aside the interminable live version of "Que Sera Sera," a poor approximation of Sly & the Family Stone.
But it turns out that such random graphs are a poor approximation because they miss two important features.
But this is a poor approximation of what the real Jobs did: his achievements were far more extraordinary, if harder to visualize.
However, our results show that this can be a very poor approximation in even quite simple models.
OS Panorama® and OS Profile® provided very poor approximations, and the other methods fail to provide any information of value.
First order orthogonal collocation and the linearization method, shown to be almost equivalent for all cases, give poor approximations.
When the initial design is small or the underlying response surface is complicated this can lead to poor approximations of the code output.
It is demonstrated that the limiting critical values for the χ̄2-type statistic provide poor approximations of the small sample critical values, and hence result in conservative tests in majority of cases.
Measurements were taken on standard specimens (50 × 50 × 300 mm) and plain prisms (80 × 150 × 500 mm) subjected to moderate curing condition (28 °C and 50% R.H). and a harsh curing condition (50 °C and 5% R.H .. ACI 209 and B3 models were found to have good prediction of experimental shrinkage strains in specimens cured in humidity room while GL2000 and Sakata models showed poor approximations.
