'week'
the survey is conducted every week
'mnth'
the survey is conducted every month
'qtr'
the survey is conducted every quarter
'0.5 wk'
the survey is conducted twice every week
'2 wks'
the survey is conducted every 2 weeks
'0.25 mnth'
the survey is conducted four times every month
'0.5 yr'
the survey is conducted twice every year
