Waldman et al, 2006, “Does Television Cause Autism”

Presented by Joseph Guse for Econ 398, Fall 2010

(revised, Fall 2012)

Autism• Symptomatic Definition.

– Impaired language development (not Aspergers)– Social interaction impairment, Mind-blindness– Obsessive and Repetitive Behaviors

• Need for stability and predictability– Symptoms apparent by age 3.– 4X more common in boys

• Etiology– Genetic – Home Environment– Physical Environment– Genetic with Environmental Triggers

• What is it really? Competing theories– Attention Disorder– Executive Function Disorder– Mind-blindness

Autism Trends

• 1970: 1 in 2500• 1992 – 1999: 400% increase – Probably due in large part to DOE reporting which

started in 1991.• 1999 – 2003: Doubled Again!• 2005 Rates in Sample• CA: .0018• OR: .0068• WA: .0023

Somali Immigrant ClustersNYTimes, March 16, 2009

• Minneapolis: 25 percent of the children in preschool classes [for autistic children] are Somali, while only 6 percent of public school enrollment is

Somali.• Stockholm: Somalis were in classes for autistic children at three times the

normal rate.• “ The city is welcoming and social benefits are generous, but many live a

life apart as conservative Muslims, the women in head scarves and long dresses.”

• “People are so isolated in their apartments here.”

Competing Theories on Trend and Causes

• Not happening. – DOE reporting– Diagnosis. (criteria broadening, classification)

• Vaccines. (Mercury)• Vitamin D. Warnings about skin cancer• Air Pollution• Television

Anecdotal Evidence that(1)It really IS happening

(2) It could be TV.

• California Data. Been keeping data since 1969 at 21 regional developmental disorder centers.– 1980 cohort has double rate as 1970– 1986 cohort has double rate as 1980– Relationship with Trends in Video Exposure

• Attention Deficit Disorder. 1 hr TV -> 10% increase in Prob(ADHD). Reverse Causality?

• Behavior of “High Risk” Infants. Failure to disengage from dynamic colorful images.

• Amish. Should be hundreds of cases among the Amish in PA, if they experience the same hazard rate. But there fewer than 10 cases. They don’t watch TV. (Of course, they have very different lifestyles in many ways.)

Empirical Strategy IPrecipitation as Exogenous Variation

• IV Approach: Precipitation– Use ATUS to establish that precipitation and TV

exposure are correlated– Run various regressions of Autism rates on Precip.Advantage:

Positive correlation cannot be explained by reverse causality: Autism most likely does not cause rain and snow.

Data for Part I.iEstablishing link between weather and TV viewing.

• Precip Data: raw data is from daily weather data from the National Climactic Data Center’s 8000 weather stations across the U.S.– Use avg across all stations in county linked to

observation in the ATUS.• TV Watching: 2003 ATUS

“First Stage” RegressionDidn’t really do 2SLS or even 2-Sample 2SLS, but you get the idea…

NOTE: THIS IS ONLY A PORTION OF AUTHORS’ Table 2

Data for Part I.iiEstablish link between Precip and Autism

• Focus on Three States (CA, WA and OR) with high precip variability.

• Most convincing specs: – OR: county-level age-specific autism rates in 2005

for children born between 1987 and 1997– CA: County-level birth cohort specific autism rates

measured when cohort is 8 y.o.

“2nd Stage” Part 12005 Autism Rates and Precip

2nd Stage Part II:Age-Specific Data

Part II: Cable TV Diffusion

• Data: autism rates for each cohort born between 1972 and 1989 at the county level in CA and PA

• Avoids satellite era.• Cable TV Data source: Television Factbook• Drop counties with poor over-air reception• Run several specs, including FE (table 7)

Doubts may remainPositive Correlation Consistent with several Hypotheses:

• Author’s basic logic:Precip -> TV -> Autism

• Could be something else about rainy weather or being indoors and have nothing to do with TV per se.

Precip -> Indoors -> REAL CAUSE -> Autism

Where R.C. = Low VitD? Indoor Air Quality? Low Exercise?

TV Could be further up causal chain: E.G

Weather Time Indoors TV

Real Cause

Autism

Improvements?

• Two Sample IV• More weather variables: cold, heat

Critique from a Non-EconomistTee Guidotti (2005) “Evidence of Causation” Archives of Environmental and

Occupational Health.