To summarize the evidence regarding potential adverse events in an accurate, concise, practical and standardized manner, we established the categories of causality conclusions. These categories are used throughout the site.
| Categories | Definitions |
| Vaccines can cause the event. | The evidence shows a clear association between the event and at least one vaccine routinely recommended in the U.S. |
| Vaccines did cause the event. | The evidence showed a clear association between the event and at least one previously recommended vaccine. However, these vaccine(s) are no longer used in the U.S., if they ever were. |
| Vaccines have not been shown to cause the event. | The evidence of an association between the event and vaccines currently routinely recommended to the general population in the United States is insufficient or non-existent. |
| Vaccines do not cause the event. | The evidence shows clear lack of association between the event and vaccines currently routinely recommended to the general population in the United States. |
