Research in Criminal Justice, sampling

For conducting research in Criminal Justice, sampling is a foundational factor for great discoveries. Which of the groups listed below do you think are the most difficult to sample within criminal justice? Why did you select that group? What are at least two challenges to sampling the group that you selected? How do you think you, as a researcher, can overcome these challenges?

Female domestic violence victims
Homeless population
LGBTQ assault victims
Victims of hate crimes
Substance users and/or abusers
Noncitizen victims of crime

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