Translations:Advanced Field Epi:Manual 1 - Disease Investigation/290/en
| style="background-color:#ffffff;border:0.5pt solid #00000a;padding-top:0cm;padding-bottom:0cm;padding-left:0.199cm;padding-right:0.191cm;"| * May be difficult to establish causality
- Can't estimate prevalence or incidence or exposure proportions
- Rely on access to historical data or recall
- Difficult to validate data
- May be affected by variables for which data is not collected
- Selection of controls often difficult