Materials and methods
2.1. Sample selection and diary recruitment
We drew a sample of 15,000 fishing licenses sold to women
aged 18 to 48 (who would reach a maximum age of 50 [considered
the end of the childbearing years] at the end of our two-year
study1
) who lived in counties bordering the Great Lakes (i.e., Great
Lakes coastal region). We drew the sample by state in proportion
to the number of licenses sold in each state to WCBA who lived in
the Great Lakes coastal region.
We sent invitation letters to each member of the sample in
February 2014. The letter described the study and what would be
required of participants. It also offered a financial incentive up to
$20 for participation in the project, and provided a link to a signup
page on the Internet. We provided a postage-paid return
postcard for people to opt out of the study because they did not
eat fish, did not have regular Internet access, or were not interested
in participating. We sent a follow-up letter to all invitees a
week later encouraging participation.
We made telephone calls to those who did not sign-up or return
a postcard to encourage participation and allow sign-up directly
over the telephone. Calling ceased in a particular state when
the quota of participants had been reached for that state. During
the study sign-up process we obtained email addresses and then
checked them by sending out a study participation verification
email. Email was then used for all communication with study
participants.
2.2. Diary data collection
We collected fish consumption information for 16 weeks from
May 18 through September 6, 2014. Participants recorded data in
two-week blocks. Participants could record information as many
times as they wished during the two-week period. Every two
weeks we sent an email invitation to participants to signal the
start of the next two-week period and remind them that the
previous two week-period was ending. When a two-week period
ended, we sent up to three reminders to participants who had not
completed entering data for the period to finish recording their
information for the period. Participants earned financial incentives
for each period completed and received a bonus at the end if they
completed reporting for every period.
We gave each participant a link unique to them to access their
personal fish consumption diary on the Internet. On the initial
page, participants saw information for the eight two-week periods
of the study, showing completed periods and incentives earned.
On the next page we asked participants to record whether or not
they ate fish on each day in the current two-week period. For each
day they indicated they ate fish, another page opened asking the
number of fish meals they had eaten on that day. For each meal
reported, participants recorded whether the fish was purchased
(at a store or restaurant) or sport-caught (i.e., fish caught by you or
someone else), the species eaten, the portion size, and (for sportcaught
fish) where the fish was caught. We provided a list of fish
species, including the most commonly consumed purchased fish
and those with consumption guideline recommendations, along
with a text box to record species not on the list. For sport-caught
species, we listed only those with consumption guideline recommendations
and provided an “other” option. Participants indicated
portion size in reference to a picture of a 6 oz. cooked
(170 g) portion of salmon (Fig. 1); we asked participants if the meal
they ate was larger, smaller, or the same size as the picture.
We obtained data on participant age from fishing license records.
We gathered data on other socio-demographic characteristics,
such as education and race, using an online survey conducted
during the last 2-week period of diary data collection.2