Table 2 Studies Included for Final Review

Harris et al. (2015) [7]

Cohort

VIQ

Kaufman Brief Intelligence Test (KBIT-2)

The mean difference in IQ points associated with an increase in PM_2.5

\({\mathrm\beta}_{VIQ}=\frac{-1.0\;points}{2.5\mathrm\mu g/m^3}\)

-0.40

Estimates were based on a “minimal model” which was adjusted for child sex and age at cognitive testing. Change in IQ was reported for each 2.5μg/m³ increase in PM_2.5. values were divided by 2.5 to yield IQ points lost per 1μg/m³ increase in PM_2.5)

PIQ

\({\mathrm\beta}_{\mathit P\mathit I\mathit Q}=\frac{-0.4\;points}{2.5\mathrm\mu g/\mathrm m^3}\)

-0.16

Ni et al. (2022) [11]

Cohort

FSIQ

Stanford-Binet Intelligence Scales, Fifth Edition (SB-5) and the Wechsler Intelligence Scale for Children, Fifth Edition (WISC-V), and the Wechsler Preschool & Primary Scale of Intelligence, Fourth Edition (WPPSI-IV)

The beta coefficient of the change in IQ points per 2μg/m³ increase in PM_2.5

\({\mathrm\beta}_{FSIQ}=\frac{-0.26\;points}{2\mathrm\mu g/m^3}\)

-0.13

Estimates based on Model 2, the “primary model”, which controlled for child sex, age, study site, child race, maternal education, log-transformed region, inflation-adjusted household income, household members, an interaction between household members and income, material status, maternal age at delivery, birth order, pregnancy smoking, pregnancy alcohol consumption, maternal depression, maternal IQ, child second-hand smoke exposure, and Child Opportunity Index (domains of educational and economic opportunity) in the corresponding window of PM_2.5 exposure. Ni and colleagues originally reported IQ points lost per 2μg/m³ increase in PM_2.5 values were divided by 2 to yield IQ points lost per 1μg/m³ increase in PM_2.5)

\(\mathrm\beta=\frac{\triangle\;IQ\mathit\;points}{\triangle\;{PM}_{\mathit2\mathit.\mathit5}\;(linear\mathit\;coef\mathit\;ficient)}\)

Porta et al. (2016) [9]

Cohort

FSIQ

Wechsler Intelligence Scale for Children-III edition (WISC-III)

The beta coefficient of the change in IQ points per 10μg/m³ increase in PM_2.5

\({\mathrm\beta}_{FSIQ}=\frac{-1.9\;points}{10\mathrm\mu g/m^{\mathit3}}\)

-0.19

All models were adjusted for gender, child age (in months) at the time of cognitive test, maternal and paternal educational level, socioeconomic index at birth, maternal age at delivery, maternal smoking during pregnancy, number of older siblings, psychologist who administered the cognitive test, and inversely weighted for the probability of participation at baseline and at the followup (to reduce attrition bias). Porta and colleagues originally reported IQ points lost per 10μg/m³ increase in PM_2.5 values were divided by 10 to yield IQ points lost per 1μg/m³ increase in PM_2.5 \(\mathrm\beta=\frac{\triangle\;IQ\mathit\;points}{\triangle\;PM_{2.5}\mathit\;(linear\mathit\;coef\mathit\;ficient)}\)

PIQ

\({\mathrm\beta}_{PIQ}=\frac{-4.1\;points}{10\mathrm\mu g/m^3}\)

-0.41

VIQ

\({\mathrm\beta}_{VIQ}=\frac{-0.44\;points}{10\mathrm\mu g/m^{\mathit3}}\)

-0.044

Seifi et al. (2021) [12]

Cross-sectional

FSIQ

Raymond B. Cattle Scale I-A

The difference in average IQ of children residing in three geographical locations with low, intermediate, and high M_2.5 exposure levels.

\(\mathrm\beta=\frac{\left(-21.33\right)\left(8.23\right)+\left(-2.33\right)\left(-0.87\right)+\left(23.67\right)\left(-8.37\right)}{\left(-21.33\right)^2+\left(-2.33\right)^2+\left(23.67\right)^2}\)

-0.36

All models were adjusted for age, gender, economic conditions, maternal education, and type of delivery. Seifi and colleagues reported the difference in average IQ points from three different groups of children residing in low, intermediate, and high PM_2.5 exposures. PM_2.5 was found to be 38.97±16.87 μg/m³, 58±23.94 μg/m³, and 84.18±31.32 μg/m³, respectively. The IQ of children in the area with high pollution was 7.48 lower than that in moderate pollution and 16.628 lower than that in the area with low pollution. To re-express these data as a linear relationship, we created a scatter plot of IQ change vs. PM_2.5 levels for the three groups on a graph and calculated a line of best fit using Stata statistical software.

\(\mathrm\beta=\frac{\sum(x_{\mathit i}\mathit-x)(y_{\mathit i}\mathit-y)}{\sum{(x_{\mathit i}\mathit-x)}^2}\)

Where is the mean PM_2.5 levels for each group and is the IQ differences for each group

Sun et al. (2023) [8]

Cohort

FSIQ

Wechsler Abbreviated Scale of Intelligence (WASI)

Beta coefficient representing the change in IQ per 5μg/m3 increase in PM2.5 exposure

\({\mathrm\beta}_{FSIQ}=\frac{-1.34\;points}{5\mathrm\mu g/m^{\mathit3}}\)

-0.27

Models adjusted for maternal factors (age, BMI before pregnancy, IQ, parity, education, intake of folic acid in early pregnancy, depression in early pregnancy), paternal factors (education), gestational weeks, and trimester-specific temperature and humidity. Sun and colleagues originally reported IQ points lost per 5μg/m³ increase in PM_2.5 values were divided by 5 to yield IQ points lost per 1μg/m³ increase in PM_2.5

\(\mathrm\beta=\frac{\triangle\;IQ\mathit\;points}{\triangle\;PM_{\mathit2\mathit.\mathit5}\;(linear\mathit\;coef\mathit\;ficient)}\)

Wang et al. (2017) [10]

FSIQ

Wechsler Abbreviated Scale of Intelligence (WASI)

The mean difference in IQ points associated with interquartile increases in PM_2.5

\({\mathrm\beta}_{FSIQ}=\frac{-2.00\mathit\;points}{21.13-16.09\mathrm\mu g/m^{\mathit3}}\)

-0.40

Estimates based on “Adjusted Model IId” which incorporated both within-family (random intercepts and slopes for PM_2.5 effects) and within-individual (random intercepts) covariances. These models were adjusted incrementally for two sets of covariates: (1) individual and family characteristics—age (continuous or dichotomized into pre-/early-adolescence vs. emerging adulthood), sex, race/ethnicity, family SES, and parental cognitive abilities; and (2) neighborhood characteristics—neighborhood SES, greenspace (1000m radius, 1 year preceding the test), traffic density (300m radius), and parent-reported neighborhood quality.

PIQ

\({\mathrm\beta}_{PIQ}=\frac{-3.08\;points}{21.13-16.09\mathrm\mu g/m^{\mathit3}}\)

-0.61

Wang et al. reported PM2.5 concentrations in interquartile ranges: Q1 (2.14-16.08μg/m3 ), Q2: (6.09 - 18.67 μg/m³), Q3: (18.68 - 21.13 μg/m³), Q4: (21.14 - 25.36 μg/m³). To re-express the effect estimate as a slope of the relationship between PM_2.5 concentration and IQ, we divided the reported IQ points lost by the interquartile range for PM_2.5 (i.e. the 75th minus the 25th percentile of the distribution), which was identified to be 5.04 μg/m³

\(\mathrm\beta=\frac{\triangle\;IQ\mathit\;points}{\triangle\;PM_{\mathit2\mathit.\mathit5}(Q\mathit4\mathit/Q\mathit3\mathit\;boundary\mathit-Q\mathit2\mathit/Q\mathit1\mathit\;boundary)}\)