Do Low Levels of Blood Lead Reduce Children's Future Test Scores?

Probably not a substantial claim: may not pass S3 (load-bearing).

Individual blood lead levels generally declined in a household after a lead-safe certificate was issued.

“Individual blood lead levels generally declined in a household after a certificate has been issued (Rogers et al. 2014).”

• cites Rogers et al. 2014 sourceSupported

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African American and Hispanic children and children who always receive free school lunch have higher mean blood lead levels (4.2, 3.6, and 3.9, respectively).

“African American and Hispanic children both have higher mean levels, as do children who always receive free school lunch (4.2, 3.6, and 3.9, respectively).”

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Estimates using the subsample with multiple children and including address fixed effects are remarkably similar to those presented above, although the IV specification based on predicted certificates is somewhat larger than before.

“Again, the results are remarkably similar to those presented above, although now the IV specification based on predicted certificates is somewhat larger than before.”

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Eighty percent of all children with a Rhode Island birth certificate are screened at least once, and the screening rate remained constant throughout the study period.

“Compared with a national lead screening rate of only 25 percent, 80 percent of all children with a Rhode Island birth certificate are screened at least once, and the screening rate remained constant throughout the study period, suggesting that the demographics of children screened also likely remained constant.”

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Table 2 showed that African Americans and children eligible for free lunch experienced greater average reductions in blood lead levels over the period examined.

“Table 2 showed that African Americans and children eligible for free lunch experienced greater average reductions in blood lead levels over the period we examine.”

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Minority children are more likely to have mean blood lead levels above 5: 30 percent of African American, 23 percent of Hispanic, and 27 percent of always free lunch children, compared to 14 percent of white children.

“Minority children are also more likely to have high mean scores, with 30 percent of African American, 23 percent of Hispanic, and 27 percent of always free lunch children having levels above 5 (compared to 14 percent of white children).”

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Measurement error is a considerable problem and tends to lead to significant attenuation in the estimated effect of lead exposure on test scores.

“The results of these estimations suggest that measurement error is a considerable problem and that it tends to lead to significant attenuation in the estimated effect of lead exposure on test scores.”

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For reading, the IV estimates are statistically significant and roughly three times as large as the OLS estimates in the first column.

“The second column of Table 8 shows that for reading, the IV estimates are statistically significant and roughly three times as large as the OLS estimates in the first column.”

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The OLS estimate based on imputed values is quite similar to the estimate shown in Table 3A.

“Given this high degree of correlation in the measures, it is not surprising that the OLS estimate based on these imputed values shown in panel A is quite similar to the estimate shown in Table 3A.”

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Children with at least one lead screen are slightly more disadvantaged along most maternal characteristics than those without a lead screen, except birth weight, which is the same for the two groups.

“Using vital statistics data to compare the maternal characteristics (race, education, and marital status) of children with a blood lead level (80 percent) to those without a blood lead level (20 percent), we find that those with at least one lead screen are slightly more disadvantaged along most measures, with the exception of birth weight, which is the same for the two groups.”

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Adding census tract fixed effects has little impact on the estimated effects of lead once individual-level variables are included, suggesting little residual confounding due to omitted variables bias.

“effects of lead once individual-level variables are included in the model suggesting that there may actually be little residual confounding due to omitted variables bias in this instance.”

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Twelve percent of children were substantially below proficient in reading and 16 percent in mathematics.

“Twelve percent of children were “substantially below proficient” (defined as a score less than 30) in reading, and 16 percent in mathematics.”

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Hausman tests suggest that estimates based on the first instrument differ significantly from OLS, but IV estimates based on the certificate program instrument do not differ significantly from OLS.

“Hausman tests of the equality of the OLS and the two IV estimates suggest that while estimates based on the first instrument (alternative measures for the same child) differ significantly from the OLS estimates, the confidence intervals are wide enough that the IV estimates based on the certificate program instrument do not differ significantly from the OLS estimates (Appendix Table 4).”

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For the lifetime imputed measure, the OLS estimate is again quite similar to that discussed above, while the IV based on the predicted certificate is much larger than any previous estimates.

“The OLS estimate is again quite similar to that discussed above, while the IV based on the predicted certificate is much larger than any of the previous estimates.”

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OLS point estimates in the smaller sample of children with at least two tests are smaller than full-sample geometric mean estimates, consistent with an average being less noisy than a single measure.

“The point estimates in this sample are smaller than those shown in the full sample and based on the geometric mean (Tables 3A and 3B), consistent with an average being less noisy than a single measure.”

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The overall estimated effect of a predicted certificate on blood lead levels is strongly negative, and is much more strongly negative for groups with high initial blood lead levels, consistent with these groups being most impacted by new lead mitigation policies enacted in 1997.

“The overall estimated effect of a predicted certificate on blood lead levels is strongly negative, and is much more strongly negative for the groups with high initial BLLs consistent with these groups being the most impacted by the new lead mitigation policies enacted in 1997.”

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Interactions in column 2 suggest that the total number of certificates in the tract was more highly predictive of having a certificate in the child's home if the child was African American or Hispanic, or always eligible for free lunch.

“The interactions in column 2 further suggest that the total number of certificates in the tract was more highly predictive of having a certificate in the child’s home if the child was African American or Hispanic, or always eligible for free lunch.”

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Whether the home ever received a certificate over the sample period is highly predictive, as are some census tract-level variables such as median family income and the share of newer housing, both negatively associated with having a certificate in the home.

“Of course, whether the home ever received a certificate over the course of our sample period is also highly predictive as are some of the census tract-level variables such as median family income and the share of newer housing, both of which are negatively associated with having a certificate in the home.”

May combine two claims. The quote only partly states this claim.

The neighborhoods with the biggest gains in certificates and reductions in child lead levels were predominantly African American and poor and remained so after the lead clean-up.

“These neighborhoods were also predominantly African American and poor and remained so after the lead clean-up.”

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The estimated increase in the probability of being less than proficient rises from 0.47 to 0.96 percentage points in reading, and from 0.38 to 0.79 in math.

“The estimated increase in the probability of being less than proficient rises from 0.47 percentage points to 0.96 percentage points in reading. The corresponding increase for math is from 0.38 to 0.79.”

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The gains in test scores were greatest in the groups most affected by the certificate program and showing the greatest declines in blood lead levels.

“However, the gains were greatest in the groups that were most affected by the certificate program and showed the greatest declines in BLLs.”

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Overall, 40 percent of children have at least one blood lead measure above 5 and 9 percent have a measure above 10 micrograms per deciliter.

“Note that it is not at all unusual in Rhode Island for a child to have a single BLL above 5 or even above 10 micrograms per deciliter—overall, 40 percent of children have at least one measure above 5 and 9 percent have a measure above 10.”

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Both instrumental variables strategies yield estimates that are considerably larger than OLS, suggesting that measurement error is a real concern.

“Both IV strategies yield estimates that are considerably larger than OLS, suggesting that measurement error is a real concern.”

• AssumptionThe authors state this as an assumption: Measurement errors in repeated blood lead measures are uncorrelated.

Classified as probably not a substantial claim. May combine two claims.

For mathematics, the estimates are imprecise, and for both math and reading the confidence intervals encompass both the OLS estimates and the corresponding IV estimates from Table 5.

“For mathematics, the estimates are unfortunately imprecise, and for both math and reading the confidence intervals encompass both the OLS estimates and the corresponding IV estimates from Table 5.”

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Among children who were always eligible for the free lunch program, reading test scores rose by 11.2 percent and the percent substantially below proficient in reading fell from 27 to 18 percent.

“Among children who were always eligible for the free lunch program, reading test scores rose by 11.2 percent, and the percent who were substantially below proficient in reading fell from 27 to 18 percent, a remarkable improvement.”

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Neighborhoods with a greater share of old housing and higher initial child lead levels in 1997 witnessed the biggest gains in lead-safe certificates issued and the biggest reductions in child lead levels.

“Neighborhoods with a greater share of old housing (one of the primary sources of lead paint in Rhode Island), and with higher initial child lead levels (as measured in 1997), witnessed the biggest gains in the number of lead-safe certificates issued, and the biggest reductions in child lead levels.”

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Excluding observations missing birth information, OLS and first IV estimates are quite similar to those reported above; the predicted certificate IV specification is still larger than the first IV specification but is no longer statistically significant.

“Column 1 of Table 9 shows OLS and the two sets of IV estimates from a sample that excludes these observations. The OLS and first set of IV estimates are quite similar to those reported above. The predicted certificate IV specification is still larger that the first IV specification, but is no longer statistically significant.”

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Among children who never participated in the free lunch program, reading test scores rose by 5.9 percent and the percent not proficient in reading fell from 6 to 4 percent.

“For instance, among children who never participated in the free lunch program, reading test scores rose by 5.9 percent and the percent who were not proficient in reading fell from 6 to 4 percent.”

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Academic test scores average 45.5 for reading and 42.2 for math, with standard deviations of 13.

“Academic test scores range from 0 to 80, with an average score of 45.5 for reading (standard deviation of 13) and 42.2 for math (standard deviation of 13).”

Probably not a substantial claim: may not pass S3 (load-bearing).

The mean blood lead level is 3.1, well below the CDC threshold for medical intervention of 5 micrograms per deciliter.

“The mean BLL is 3.1, which is well below the CDCs threshold for medical intervention of 5 micrograms per deciliter.”

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Using the first instrument increases the estimated impact of a unit of blood lead on reading from -0.188 to -0.436 and on math from -0.124 to -0.305.

“Using this instrument increases the estimated impact of a unit of blood lead on reading (math) from −0.188 (−0.124) to −0.436 (−0.305).”

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In census-tract aggregated estimation for reading, the estimated effects are similar but slightly larger than those in Table 8; a one unit increase in blood lead levels is estimated to reduce reading scores by -1.251.

“The estimated effects are similar but slightly larger than those described in Table 8. A one unit increase in BLLs is estimated to reduce reading scores by −1.251.”

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About 15 percent of the sample are missing birth information, primarily because they were born outside Rhode Island.

“About 15 percent of our sample are missing birth information, primarily because they were born outside of Rhode Island.”

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Estimates from the second instrumental variables strategy are considerably larger but also noisier, so the paper cannot reject the null that confidence intervals encompass both the OLS and first set of instrumental variables estimates.

“The estimates from the second IV strategy are considerably larger but also noisier so that we cannot reject the null that confidence intervals encompass both the OLS and first set of IV estimates.”

• AssumptionThe authors state this as an assumption: Measurement errors in repeated blood lead measures are uncorrelated.

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Third grade test scores rose across birth cohorts in all demographic groups, while the fraction scoring substantially below proficient declined.

“Third grade test scores rose across birth cohorts in all demographic groups, while the fraction scoring substantially below proficient declined.”

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Column 3 estimates suggest that a 1 point increase in mean blood lead levels reduces reading scores by -0.335 and math scores by -0.220.

“The column 3 estimates suggest that a 1 point increase in mean BLLs is estimated to reduce reading scores by −0.335, and math scores by −0.220.”

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The reading IV estimates are about double the size of the corresponding IV estimates in Table 5.

“They are also about double the size of the corresponding IV estimates in Table 5.”

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IV estimates in Table 5, column 2 are much larger than OLS estimates: for reading the coefficient rises from -0.186 to -0.442, and for math from -0.124 to -0.305.

“The IV estimates shown in Table 5, column 2 are much larger than the OLS estimates. For reading the estimated coefficient rises from −0.186 to −0.442; for math the value rises from −0.124 to −0.305.”

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Adding birth certificate information and time-varying census tract characteristics reduces the estimated effects of lead from -0.456 to -0.326 for reading and from -0.348 to -0.216 for math, suggesting confounding could be a concern in studies with inadequate controls for family background.

“These additions reduce the estimated effects of lead from −0.456 per unit of lead to −0.326 for reading and from −0.348 to −0.216 for math, suggesting that confounding could be a concern in studies with inadequate controls for family background.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The estimate using the predicted certificate instrument is also quite similar to that shown in Table 5.

“Since now we have only one imputed measure, this method does not lend itself to our first IV strategy, but the estimate using the predicted certificate instrument is also quite similar to that shown in Table 5.”

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The effects for math in the census-tract aggregated estimation are small and imprecisely estimated.

“However, the effects for math (not shown) are small and imprecisely estimated.”

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The estimated effects of lead in these models are strongly statistically significant but relatively small.

“The estimated effects of lead in these models are strongly statistically significant but relatively small.”

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Estimates based on the average of all other tests are somewhat larger in absolute value than those based on a single randomly drawn test, consistent with averaging reducing random measurement errors.

“The latter are somewhat larger in absolute value than those in column 3 consistent with averaging reducing the effects of random measurement errors.”

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Focusing on the subsample with multiple children observed over time reduces the sample size to 26,131 children.

“Focusing on this subsample reduces the sample size to 26,131 children.”

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Lead poisoning may be one of the causes of continuing disparities in test scores because disadvantaged children have greater exposure to lead.

“Since disadvantaged children have greater exposure to lead, lead poisoning may be one of the causes of continuing disparities in test scores.”

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African American and poor children are two to three times as likely to have elevated lead levels, defined as above 5 ug/dl.

“For both these reasons, disparities in child BLLs by race and income remain, with African American and poor children two to three times as likely to have elevated lead levels, defined as above 5 ug/dl (CDC 2013).”

• cites CDC 2013Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

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The same reduction in lead reduced the probability of being below proficiency in reading by 2.6 percentage points, or 22 percent, and in math by 2.1 percentage points, or 13 percent.

“The same reduction in lead reduced the probability of being below proficiency in reading by 2.6 percentage points, or 22 percent. For math the comparable figure is 2.1 percentage points or 13 percent.”

Classified as probably not a substantial claim.

The observed gains in test scores might have been caused by other changes targeted at poor and minority children, most likely targeted educational policies.

“Of course these gains might have been caused by other changes targeted at poor and minority children; the most likely alternative candidate is targeted educational policies.”

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Although the second IV estimates are imprecise, they are substantially larger than those generated by the first IV method, perhaps providing preliminary evidence for heterogeneity in the impact of lead.

“Although these estimates are imprecise, they are substantially larger than those generated by our first IV method, which perhaps provides some preliminary evidence for heterogeneity in the impact of lead.”

Classified as probably not a substantial claim.

In 1997 Rhode Island established two programs to encourage mitigation of lead hazards in old homes.

“In an effort to reduce childhood exposure to lead, in 1997 Rhode Island established two programs to encourage mitigation of lead hazards in old homes.”

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There may be considerable measurement error in blood lead levels, which complicates estimation.

“As discussed above, estimation is complicated by the fact that there may be considerable measurement error in blood lead levels.”

• cites Ashenfelter and Krueger (1994)Not checked — no full text of the source
• cites Chalfin and McCrary (forthcoming)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

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The first instrumental variables strategy instruments one blood lead measure with another, assuming each is a noisy measure of true lead exposure and that measurement errors are uncorrelated, to purge measurement error.

“If we regard each as a noisy measure of the child’s true lead exposure and assume that the measurement errors are uncorrelated, then we can instrument one measure with another in order to develop an estimate that is purged of measurement error.”

• AssumptionThe authors state this as an assumption: Measurement errors in repeated blood lead measures are uncorrelated.

Classified as probably not a substantial claim.

Using the predicted certificate purges the instrument of potential endogeneity associated with the take-up decision.

“By using the “predicted certificate,” we purge the instrument of any potential endogeneity associated with the take-up decision.”

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The finding of larger effect sizes for reading relative to math is consistent with some epidemiological studies documenting stronger relationships between lead and verbal functioning.

“The finding of larger effect sizes for reading relative to math is consistent with some epidemiological studies that have also documented stronger relationships between lead and verbal functioning (e.g., see Bellinger, Stiles, and Needleman 1992 as an example and CDC 2004 for a review of estimated effects of lead on verbal IQ and performance IQ).”

• cites Bellinger, Stiles, and Needleman 1992 sourceNot checked — no full text of the source
• cites CDC 2004Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

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Disadvantaged children may suffer double jeopardy in the sense that they are both exposed to greater levels of lead and experience greater impacts of the same exposure.

“Disadvantaged children may suffer double jeopardy in the sense that they are both exposed to greater levels of lead and experience greater impacts of the same exposure.”

Probably not a substantial claim: may not pass S4 (based).

The predicted certificate instrument is not a function of unobservable child or family characteristics that influence certificate take-up and might also be correlated with test scores.

“Importantly, the instrument, predicted certificate, is not a function of μi, the unobservable characteristics of the child or family that influence certificate take-up and that might also be correlated with test scores.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

These estimates seem generally consistent with estimates in the epidemiological literature, though direct comparisons are difficult because of differences in methods, adjustments for measurement error, and the higher lead levels examined in previous work.

“These estimates seem generally consistent with estimates in the epidemiological literature, though direct comparisons are difficult because of differences in methods, adjustments for measurement error, and the higher lead levels examined in previous work.23”

• cites [23]Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

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For the average public school child, eliminating lead by reducing lead levels from 2.7 to zero micrograms per deciliter increased mean reading and math scores by 1.18 and 0.82 points, respectively, corresponding to 9 and 6 percent of a standard deviation.

“These figures suggest that for the average public school child, eliminating lead (by reducing lead levels from 2.7 to zero micrograms per deciliter) increased mean reading and math scores by 1.18 and 0.82 points, respectively, corresponding to 9 and 6 percent of a standard deviation.”

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Black children in homes that had not yet received a certificate had blood lead levels two micrograms per deciliter higher than other black children, and this gap was reduced to zero when a certificate was obtained.

“This comparison suggests that black children in homes that had not yet received a certificate had BLLs two micrograms per deciliter higher than other black children and that this gap was reduced to zero when a certificate was obtained.”