As questionnaires were mailed to families 4–7 years after their initial enrollment in the study, many had moved and could no longer be contacted. Of the 334 eligible families to whom questionnaires were mailed, 128 were returned undeliverable, presumably because the family had moved. Of the 206 questionnaires that were not returned undeliverable, all but 56 were returned completed (72.8%). Mothers who returned completed questionnaires were somewhat more likely to be Caucasian (88% vs. 78.6%) and to have completed college (73.3% vs. 68.4%) than those who could not be contacted, or who failed to return a completed questionnaire.
We conducted an item analysis of the 24 questions (available upon request). Q5F (‘avoids taking risks’) had been classified as a ‘feminine’ question. However, the mean (2.6) and median (3.0) were equal in boys and girls in our sample. Similarly, the mean (3.2) and median (4.0) for Q5A (‘likes to explore new surroundings’), which was classified as a masculine question, were the same in boys and girls. As these items were not sex-dimorphic in our sample, they were dropped, reducing the total number of items to 22 and forming the modified instrument (PSAI-M), which we used in all analyses. As shown in , the mean and standard deviations of the composite scores obtained using PSAI-M in our population were in close agreement with those for several thousand children obtained using the original PSAI (Golombok et al., 2008
Summary statistics for modified Pre-School Activities Inventory (PSAI) compared with published data on PSAIa
None of the urinary concentrations of phthalate metabolites other than those of DEHP and DBP were associated with play behaviour scores in boys or girls in either univariate or initial multivariate analyses (p-values were between 0.23 and 0.99 for all metabolites other than those of DEHP and DBP; data not shown). Nor were the concentrations of any phthalate metabolites associated with play behaviour in girls. Therefore, the remaining analyses were limited to metabolites of DEHP: mono-(2-ethylhexyl) phthalate (MEHP), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) and mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) as well as their sum (denoted RDEHP), and metabolites of DBP: mono-n-butyl phthalate (MnBP) and mono-isobutyl phthalate (MiBP), as well as their sum (denoted ΣDBP) in relation to play behaviour scores in boys.
Summary statistics for the three PSAI-M scores and other covariates are shown in . Mean parental attitude scores (PAB and PAG) were close to neutral, with parents of girls somewhat more likely to discourage sex-atypical play (A value of 3 indicates the parent would neither encourage nor discourage such play. The sum of these, combining attitudes of both parents, was included in multivariate models, for which a value of 6 indicates neutrality).
Summary of Pre-School Activities Inventory (PSAI) scores and covariates
Phthalate metabolite concentrations in our sample (shown in ), are consistent with those reported in a national sample (CDC, 2005
). We initially included creatinine concentration in these models to adjust for urinary dilution, However, creatinine concentration was not retained in final models, as point estimates were close to zero (p
-values = 0.52–0.90) and removing this variable had little influence on the effect estimates.
Mean and percentiles for DEHP and DBP metabolite concentration in prenatal urine by sex
The two metabolites of DBP, as well as their sum, were associated with a decreased (less masculine) composite score in boys. Regression coefficients were −4.53, −3.61 and −4.20 (p = 0.01, 0.07 and 0.04) for MiBP, MnBP and their sum (denoted ΣDBP) respectively (). Of the DBP metabolites, only MiBP was associated (positively) with the feminine score (coefficient 2.48, p = 0.07). The (weak) negative associations between DBP metabolites and the masculine score were unremarkable.
Regression coefficients (95% CI) for boys’ Pre-School Activities Inventory (PSAI) scores on concentration of (log10) phthalate metabolite concentration in prenatal urine
Concentrations of two urinary metabolites of DEHP, MEOHP and MEHHP, as well as the sum of concentrations of MEHHP, MEOHP and MEHP (denoted ΣDEHP), were associated with a decreased masculine score. Regression coefficients were −3.29, −2.94 and −3.18 (p = 0.02, 0.04 and 0.04 for MEHHP, MEOHP and ΣDEHP respectively), as seen in . Associations between DEHP metabolites and the composite and feminine scores were weak (all p-values >0.36).
Regression coefficients (95% CI) for girls’ Pre-School Activities Inventory (PSAI) scores on concentration of (log10) phthalate metabolite concentration in prenatal urine
While not all associations between DEHP and DBP metabolite concentrations and play behaviour reached statistical significance at p = 0.05, all regression coefficients for the masculine and composite scores and these metabolites were negative for boys, suggesting that these metabolites are (to various degrees) associated with less masculine play behaviour. To express these in terms that are easier to interpret than the regression coefficients, we show the per cent change in the composite and masculine scores the model would predict, if the mothers’ metabolite concentration was increased from the 10th to the 90th percentile. These predicted changes are shown in . Those for which the significance probability of the underlying effect estimates reached p = 0.05 are starred.
Figure 1 Percent change in PSAI-M score expected if the phthalate metabolite concentration in boy's mother's prenatal urine was increased from the 10th percentile to the 90th percentile. Stars indicate p-values of <0.05 for regression coefficients in multivariate (more ...)
We reran these analyses excluding the Parental Attitude Scores (and their interaction with maternal education). We found that questions on parental attitude were important for some associations, but not all. Removing these questions resulted in changes to the effect estimates of between 0 and 12.5%. In particular, adding these parental attitude questions strengthened the associations between DEHP metabolites and the masculine score. On the other hand, when PAB is not included, the association between MiBP concentrations and boys’ feminine score is somewhat stronger (coefficient = 2.79, p-value = 0.048), implying more feminine play with higher DBP exposure. However, after adjusting for parental attitude this association is reduced somewhat (coefficient 2.48, p = 0.07), suggesting some negative confounding by PAB.