- Integration (Steele explains this would be the earlier stages of integration and that more extensive integration can dispel stereotypes)
- When the stereotyped group is numerically small
- Having a homogenous culture despite the existence of some diversity
On a macro level, however, I wouldn't say the power of stereotyping is contingent upon the stereotyped groups' numerical size or proportion in a particular realm. The classic example when explaining how minority-majority group relations depend on power (not group size) is South Africa, where black South Africans are a numerical majority, but are still minorities when it comes to power. Being minorities, they would be the group more at-risk of being stereotyped in ways that have major adverse consequences even though they comprise a bulk of the country's population. Here's the video.
The Root Interview: Claude Steele on How Racial Stereotypes Harm Performance (doh, guess you cannot watch the video here, so just click on the link to view it)
And then some research illustrating one of the points Steele was making -- that simply an awareness of being stereotyped can be distracting and have adverse consequences in everyday situations. This example is a little dated, but definitely falls in line with the subject matter offered above, with a specific focus on gender:
Both videos provide strong points on the subtleties of stereotyping and how stereotypes can operate in society.