Casuality - здесь причинная связь с приемом исследуемого ЛС.
Possible - возможная причинная связь.

А вообще,
Reporter: Any person who describes a suspected adverse event (AE)/adverse drug reaction (ADR) case report to the marketing authorisation holder (MAH) or the organisation responsible for pharmacovigilancc on behalf of the MAH for the drug in question, to the relevant regulatory authority (competent authority in the European Union (EU)).... The term is not synonymous with the term sender, although the reporter could also be the sender. In the EU, the reporter of an AE/ADR has to be a healthcare professional (HCP), or the report has to be medically confirmed by an HCP to qualify for reporting. In this case, the HCP is considered to be the reporter....
Т.е. casuality reporter - источник сообщения о причинной связи НЯ с приемом исследуемого ЛС.
Но можно ограничиться просто *причинная связь*. Если нужно точно, то причинная связь согласно источнику сообщения о НЯ.

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Note added at 16 час (2011-11-21 06:24:20 GMT)
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По-видимому в заголовке сокращена следующая фраза (в цитате она тоже является заголовком):

Primary Reporters' Causality Assessment
Of the 168 reports, 102 (61%) included a causality assessment. A probable or possible causal relationship was provided in 81 reports and an unlikely causal relationship in the remaining 21 reports. Of the reports with an assessment, 94% were from health care professionals.


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Note added at 16 час (2011-11-21 06:26:29 GMT)
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А в колонке, соответственно, стоят оценки. Согласно ВОЗ, они могут быть следующими:
C1 – Certain
C2 – Probable
C3 – Possible
C4 – Unlikely
C5 – Unclassifiable