Information provided by the AWSD (Aid Worker Security Database), there were 251 individual attacks in 2013. This, and the subsequent 460 workers involved or affected, is in no way separated according to the aid work the individuals participated in. Thus, all 251 attacks may have been aimed at health care clinics, but only 50 of those injured may have been health care workers; the rest may have been members of peacekeeping forces. Further more, which members of the health care system are being harmed is extremely useful in future aid endeavors. Knowing who is targeted or particularly vulnerable could make the difference in the next incident.
Moreover, any data that is available can be difficult or complicated to obtain. Outside of the nuances of procuring data from different corporations or foundations, many organizations have individual categories for reporting incidents. They may even have different definitions of attacks and incidents-- eerily similar to how German and US officials view sexual assault in different lenses (German officials may often be disinclined to act unless penetration occurs, while US officials have been known to prosecute or bring charges for offenses such as groping).
These definition differences may also lead to an under reporting of incidents. While most available data contains information about abductions or fatalities, very little data can be accessed pertaining to threats or obstructions. This may also color how and what aid workers report; knowing that an incident did not culminate in a kidnapping or death may lead workers to be less inclined to report these issues, for fear of not being taken seriously. Aid workers may also feel that, during some stressful circumstances, reporting something that could be constituted as "mild" would only be a waste of time and resource.