The phrase 'do not differ much' is correct and usable in written English.
You can use it when you want to compare two or more items that are very similar. For example, "The prices of these two items do not differ much."
Up to relatively high values of the crack density, the conductivities of different disordered models do not differ much from each other.
Overall, prevalence of maternal complaints after symphysiotomy and CS do not differ much, though they are somewhat different in nature.
Whether this lack of discrimination reflects that they should not (ultimate reason), or that they cannot differentiate between males of different ploidy, because their calls do not differ much (proximate reason), remains an open question.
Despite this, the average levels of divergence between the copies do not differ much for cercariae isolated from the two different species of snails (10.5% and 11.3%).
For cases with the same θ but various Ra and a, these ratios do not differ much, meaning that θ is the controlling factor for the difference in yield stress predicted by Arrhenius viscosity and exponential viscosity.
Usually the two do not differ much.
Word lengths do not differ much: the average word used in the speeches analysed had around 4.5 letters.
His priorities do not differ much from those of his predecessors, but he may ask for more troops.
It is not particularly surprising that the average contributions of all immigrants do not differ much from those of the whole UK population.
Campaign officials also said that for all his criticism, Mr. Romney's prescriptions for dealing with Tehran do not differ much from the president's.
The rates do not differ much from what it pays elsewhere, but it can have the perks a landlord can provide to a larger building without sacrificing privacy.
