“Whether the exclusion affects its conclusion.”

Yes, if the omitted material is relevant to the conclusion.

Suppose a study asks:

“Did industrialization improve living standards?”

But it examines only:

wages;

and ignores:

working hours;

housing;

mortality;

child labor;

workplace injuries.

It may conclude:

“Industrialization substantially improved workers' lives.”

The conclusion might be misleading because relevant evidence was excluded.

But suppose the research question was specifically:

“How did nominal wages change between 1800 and 1850?”

Then omitting mortality may not invalidate the conclusion because mortality isn't directly necessary for answering that narrower question.

So:

Omission is not automatically bias.

The key question is:

Was the omitted evidence relevant to the claim being made?

If yes, and especially if its omission systematically pushes the conclusion in one direction, then the study may produce a distorted or misleading picture.

“False” is stronger than “misleading.”

A study can contain individually true statements but still produce a misleading overall conclusion because of selective omission.