In Hong Kong, discrimination on the grounds of gender, family status, disability, and race is made unlawful by legislation since the introduction of the Sex Discrimination Ordinance (Cap. 480), Disability Discrimination Ordinance (Cap. 487), Family Status Discrimination Ordinance (Cap. 527), and Race Discrimination Ordinance (Cap. 602). However, there are circumstances where discrimination cannot be established, even in the presence of prima facie evidence.

Required: Give a specific example for each of the above four discrimination categories where discrimination cannot be established in the presence of prima facie evidence. You must support your answer with adequate reasons.