The phrase "are often much smaller" is correct and usable in written English.
It can be used when comparing the size of two or more items, indicating that one group is generally less in size than another.
Example: "The new models of smartphones are often much smaller than their predecessors, making them easier to handle."
Alternatives: "tend to be significantly smaller" or "are frequently much less in size".
In the case of state-wide polls in America, the samples are often much smaller.
For a start, pools of potential partners are often much smaller than the big numbers touted by mainstream sites suggest.
The markets are often much smaller than their upper-class counterparts, often with no more than a couple of tables under white tents in front of a city park.
Clusters are often much smaller than that, with the important consequence that many are so small that when examined their electrons and electronic states can exhibit the wavelike properties of matter.
In devices like heterojunction bipolar transistors, the active regions thicknesses are often much smaller than the substrates thicknesses.
Although systems based on an AOM are often much smaller than competitors, they can be difficult to build and to learn.
Equally worrying: when an effect did appear, it was often much smaller than previously thought.
Costs range from $40 to $5,000 for a "site" which can be as large as 50 acres – if the field is planted with a single crop – but is often much smaller.
Although many European countries also run a current deficit and their total debt may be increasing in size, the rate of increase is often much smaller than that of the United States and often below the rate of growth of national income.
This results in a final architecture which is often much smaller than an radial basis functions network or an multi-layer perceptron.
The simple error estimates (11) are still quite inaccurate: the maximal error is often much smaller (see also the dashed histograms in the right panels of Figure 4).
