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Table 6 Candidate variables used for minimizing Akaike Information Criterion (AIC), via step-AIC algorithm

From: Buccal mucosa micronuclei counts in relation to exposure to low dose-rate radiation from the Chornobyl nuclear accident and other medical and occupational radiation exposures

Variable Description
first period of first mission to the Chornobyl zone
days_act duration of active work in the Chornobyl zone in days
Case_leuk case of leukemia in the study of Zablotska et al. 2013
Year_first_exposed year first exposed via work in Chornobyl exclusion zone (calculated from dose record)
Year_last_exposed year last exposed via work in Chornobyl exclusion zone (calculated from dose record)
proxya proxy interviews
proxy_str proxy status based on the cases status in the set
number1 number of missions
first_year year first exposed via work in Chornobyl exclusion zone
duration total duration of work in the Chornobyl zone in months
duration_act duration of active work in the Chornobyl zone in months
days total duration of work in the Chornobyl zone in days
tse time since first exposure in the zone until diagnosis (for cases) and reference time (for controls) in years; tse < 0 (n = 4) is set to 0
radiation non-Chornobyl work with radiation exposure
industry work in hazardous industries
oil oil or chemical industry
chemical non-Chornobyl work with hazardous chemicals
petroleum work in petroleum industry
pesticides work with pesticides
solvents work with solvents
other_chemical work with hazardous chemicals other than in petroleum industry/pesticides/solvents
age age at diagnosis (for cases) and age at reference date (for controls)
age_x age at first exposure in the zone
subtypea subtype of leukemia
subtypeclla CLL subtype
subtypecll_str CLL subtype, based on the case status, matching controls set to case status
y_dxa year of diagnosis; for controls set to −1
reference reference year set to year of diagnosis (for cases) and for controls is the same as for matched case
y_int year of interview
liqtype type of work performed in the Chornobyl zone during the first mission
flag1 additional controls re-distributed among cases
flag2 controls used in risk analysis for Phase I but now matched to their original case used in set Phase II
flag_definite certainty in the leukemia diagnosis (definite + probable/other)
Phase study phase (phase I/phase II)
COM1_EXP1 dosimetry expert’s opinion about the quality of interview during the 1st mission to the 30-km exclusion zone
COM2_EXP1 dosimetry expert’s opinion about the quality of interview during the 2nd mission to the 30-km exclusion zone
COM3_EXP1 dosimetry expert’s opinion about the quality of interview during the 3rd mission to the 30-km exclusion zone
QUES1 interviewer’s opinion on the quality of questionnaire: Did subject reply with interest?
QUES2 interviewer’s opinion on the quality of questionnaire: Did the worker remember his job in the 30-km exclusion zone?
Liquid clean-up worker with data on interviewer’s opinion about the quality of interview
Exp expert dosimetrist who prepared dosimetric questionnaire for input into RADRUE
time_int_ch time from interview to chemotherapy (date of start of chemotherapy for CLL and date of diagnosis for non-CLL)
seta cases with direct interviews
t11a if time_int_ch ≠ 99 and time_int_ch ≠ −1 and cases = 1 and proxy = 0 and −1 ≤ time_int_ch ≤ 1 then t11 = 1;else t11 = 0;
t1515a if time_int_ch ≠ 99 and time_int_ch ≠ −1 and cases = 1 and proxy = 0 and −1.5 ≤ time_int_ch ≤ 1.5 then t1515 = 1;else t1515 = 0;
t12a if time_int_ch ≠ 99 and time_int_ch ≠ −1 and cases = 1 and proxy = 0 and −1.0 ≤ time_int_ch ≤ 2.0 then t12 = 1;else t12 = 0;
t22 if time_int_ch ≠ 99 and time_int_ch ≠ −1 and cases = 1 and proxy = 0 and −2.0 < time_int_ch < 2.0 then t22 = 1; else t22 = 0
liqtype_recode type of work performed in the Chornobyl zone during the first mission recoded (from liqtype) (missing/early responders & firefighters/professional nuclear power workers/military personnel/drivers & construction workers)
num_miss number of missions to the Chornobyl exclusion zone
rad_exp study subject ever worked with radiation (other than the time the study subject spent in the Chornobyl area)
rad_radiography study subject ever worked with radiation as industrial radiographer (other than time study subject spent in the Chornobyl area)
rad_nuclear study subject ever worked with radiation in the nuclear industry (including NPP, other than time the study subject spent in the Chornobyl area)
rad_army study subject ever worked with radiation in army service (other than time the study subject spent in the Chornobyl area)
rad_other study subject ever worked with radiation other than in army/nuclear industry/industrial radiography (other than time the study subject spent in the Chornobyl area)
haz_exp study subject ever worked in a hazardous industry (specific types of chemical/electrical/road-building/other)
haz_chem study subject worked in chemical industry/oil industry (hazardous industry)
haz_el study subject worked in electrical industry (hazardous industry)
haz_road study subject worked in road-building industry (hazardous industry)
haz_other study subject worked in one of coal mining/military service/metallurgical industry/welding/gas equipment/other hazardous industries (hazardous industry)
chem_exp Has the study subject ever worked with hazardous chemicals?
chem_petrol study subject worked with petrol (petrol and agricultural pesticides/petrol and organic solvents)
chem_pest study subject worked with agricultural pesticides (petrol and agricultural pesticides/agricultural pesticides and organic solvents/agricultural pesticides and other)
chem_solva study subject worked with organic solvents (petrol and organic solvents/agricultural pesticides and organic solvents)
chem_other study subject worked with hazardous chemical other than petroleum/agricultural pesticides/organic solvents
Oblast Dnipropetrovsk/Kyiv oblast/Kharkiv/Cherkassy/Chernihiv/Kyiv-city
Educ level of education of interviewee (8 years or less school/high school/trade school/higher education)
Urban Type of settlement (city/village/other)
radtxa Has the study subject had radiotherapy for cancer treatment
chemotxa Has study subject had chemotherapy for cancer treatment
radtx_other Has the study subject ever received radiotherapy for medical conditions other than cancer
x_dental Has study subject ever had dental X-ray?
x_dental_n Number of times study subject has had dental X-ray
x_bone Has interviewee ever had bone X-ray?
x_bone_n Number of times interviewee has had bone X-ray?
x_chest Has study subject ever had chest X-ray (except fluoroscopy)
x_chest_n Number of times study subject ever had chest X-ray (except fluoroscopy)
x_other Has the interviewee ever had other X-ray examinations (than bone, chest, dental)?
x_other_n How many times interviewee had any other type (than bone, chest, dental) of X-ray examination?
fam_cancer Have any of interviewee’s relatives had any solid cancer or leukemia (mother or father, or other relative)?
  1. avariable excluded from step-AIC analysis when omitting 6 cancer cases because trivial in reduced dataset