2.6. Statistical analysis
Summary statistics for the pyrethroid data were calculated. For
concentrations below the limit of detection (LOD), an imputed value
was assigned equal to the LOD divided by the square root of 2 (Barr
et al., 2010; Hornung and Reed, 1990). A Spearman rank-order correlation
procedure was used to determine the intra-household correlations
between particular pyrethroid concentrations, with significance set at
p b 0.05.
A Spearman rank-order correlation procedure and 95% confidence
intervals (CI) were used to evaluate associations between interview
questionnaire variables and the presence of pyrethroid pesticides in
the house dust, with significance set at p b 0.05.
As part of the main MICASA study questions on pesticide use were
asked of the full cohort of 436 households in both an interview
conducted fromJanuary 2006 toMay 2007 and an interview conducted
from February 2009 to June 2010. These questions were asked of both
the male and female heads of household. Responses to these questions
allowed us to look at the consistency of reporting pesticide use among
family members as well as the consistency of reporting pesticide use
over time. In both interviews the male and female heads of household
were asked separately if either they or anyone in the household uses indoor
and/or outdoor pesticide sprays. The consistency of responses to
these pesticide use questions between the men and women from the
same household was assessed using Cohen's kappa, a measure of
chance-corrected agreement (Landis and Koch, 1977; Lin et al., 2011).