In PLCO and LSS, many methods were used to keep track of and trace participants. The most extensively used methods involved telephoning. Mail and internet searches were extensively used by many centers as well.
We know of no other published reports that have explicitly looked at extent of use of specific methods for tracking and tracing participants in large cancer screening trials. Studies assessing other interventions or desiring long-term follow-up, however, have published information on how they kept track of and found lost participants. Lusk et al
] report that in the Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), a participant contact information form was developed and completed each year by study participants. Their contact form has similarities to the FLF and PCF used in PLCO and LSS, respectively; both ALLHAT and PLCO/LSS requested that the participant provide contact information for two additional friends or relatives not residing in his or her home. Lusk et al
also report that internet and computer searches were an important resource for finding lost participants. This concurs with our findings of the extensive use of web-based searches. While we know of two other studies that have reported on how lost participants were located, the study populations, inner-city children with asthma [4
] and persons who did not attend a tuberculosis clinic after release from jail [5
], are dissimilar to PLCO and LSS and therefore detailed comparisons are not warranted. Nevertheless, each study reported at least one method similar to a method used in PLCO and LSS: Senturia et al
] report using reverse-lookup searches and Menendez et al
] report using telephone calls to aid in finding participants.
Because PLCO and LSS participants were healthy when enrolled, and most remained cancer-free throughout follow-up, our results contribute valuable information as to how studies of chronic disease prevention (including secondary prevention) in older Americans can keep track of and trace their participants. A comparison with the ALLHAT study indicates that tracking and tracing methods successfully used in treatment and prevention trials may be similar to those used in PLCO and LSS, but because the motivations for participating in each type of study may differ (personal benefit versus altruism, respectively), it is important to consider whether certain methods are more effective when reasons for participation and continued affiliation differ. There are many challenges in collecting information from an older study population [6
]. Decline in physical and mental health, relocation after retirement, placement in assisted living or nursing home facilities, and loss of interest are correlated with advancing age. Therefore, it is of the utmost importance that tracking and tracing activities be flexible enough to handle such situations. Coordinators informally reported that the inclusion of a question on the BLF, FLF, and PCF requesting the names and contact information for two persons who do not reside in the participant’s household was very helpful in locating participants who had moved to senior living facilities.
We are not surprised that use of some tracking and tracing methods varied by center. Our centers were different in terms of location, type of facility, and research infrastructure, not to mention lifestyle of participants. For example, persons who live in rural areas change residences less frequently than those who live in inner cities; therefore, mailings to rural participants may be more fruitful, and unique methods may be necessary for transient populations. Screening centers that enrolled many HMO participants may have had access to databases that provided up-to-date contact information, and may not have needed to use other methods. Centers that were located in areas where residents are more trusting and cooperative probably could use direct methods of contact (like phoning or mailing) most of the time. Centers in other locations may have needed to use methods, such as internet searches, that did not involve contacting the participant.
Strengths of our study include that data on tracking and tracing at individual centers was collected through querying of center coordinators, personnel who were on the front line of study activities. Shortcomings of our study include that we were unable to use quantitative data to determine which method resulted in removal of the most participants from tracing status, or prevented the participants from entering tracing status. Furthermore, we were unable to collect data in a prospective, non-subjective manner; the accuracy of our results therefore depends on the recall of the research team members who completed the questionnaire. We believe that our data demonstrating a reduction in the percentage of PLCO participants in tracing status over time indicates that invaluable experience was gained and methods were optimized; however, we cannot rule out the possibility that the decrease indicates the gradual culling of a small, finite group of uninterested participants. The fact that no similar decrease was observed during LSS argues against that possibility.