Birth order and risk of non-hodgkin lymphoma--true association or bias?
There is inconsistent evidence that increasing birth order may be associated with risk of non-Hodgkin lymphoma (NHL). The authors examined the association between birth order and related variables and NHL risk in a pooled analysis (1983-2005) of 13,535 cases and 16,427 controls from 18 case-control studies within the International Lymphoma Epidemiology Consortium (InterLymph). Overall, the authors found no significant association between increasing birth order and risk of NHL (P-trend = 0.082) and significant heterogeneity. However, a significant association was present for a number of B- and T-cell NHL subtypes. There was considerable variation in the study-specific risks which was partly explained by study design and participant characteristics. In particular, a significant positive association was present in population-based studies, which had lower response rates in cases and controls, but not in hospital-based studies. A significant positive association was present in higher-socioeconomic-status (SES) participants only. Results were very similar for the related variable of sibship size. The known correlation of high birth order with low SES suggests that selection bias related to SES may be responsible for the association between birth order and NHL.
Grulich
Andrew E
AE
HIV Epidemiology and Prevention Program, National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, Sydney, New South Wales 2052, Australia. agrulich@nchecr.unsw.edu.au
Vajdic
Claire M
CM
Falster
Michael O
MO
Kane
Eleanor
E
Smedby
Karin Ekstrom
KE
Bracci
Paige M
PM
de Sanjose
Silvia
S
Becker
Nikolaus
N
Turner
Jenny
J
Martinez-Maza
Otoniel
O
Melbye
Mads
M
Engels
Eric A
EA
Vineis
Paolo
P
Costantini
Adele Seniori
AS
Holly
Elizabeth A
EA
Spinelli
John J
JJ
La Vecchia
Carlo
C
Zheng
Tongzhang
T
Chiu
Brian C H
BC
Franceschi
Silvia
S
Cocco
Pierluigi
P
Maynadié
Marc
M
Foretova
Lenka
L
Staines
Anthony
A
Brennan
Paul
P
Davis
Scott
S
Severson
Richard K
RK
Cerhan
James R
JR
Breen
Elizabeth C
EC
Birmann
Brenda
B
Cozen
Wendy
W
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001722:Birth Order; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008228:Lymphoma, Non-Hodgkin / Q000145:classification / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D035781:Siblings; D012959:Socioeconomic Factors; D055815:Young Adult