Question

Hypothesis 1: Mercury in thimerosal caused neurological damage in children, and is at least partly responsible for
the increase in autism diagnoses.

Hypothesis 2: Te rate of autism incidence is not increasing, only the rate of autism diagnoses, as greater awareness
of the syndrome and increased screening of children yields more positive diagnoses of autism.

What are the observations that led to the generation of the above hypotheses? Do both hypotheses make testable predictions? How could you test them?

Answer 1

Hypothesis 1: Mercury in thimerosal caused neurological damage in children, and is at least partly responsible for the increase in autism diagnosis.

Increased incidents of autism after the introduction of thimerosal vaccines or increased reports of autism-related symptoms in babies after a few days to a few months of vaccination led to the hypothesis.

Hypothesis 2: Te rate of autism incidence is not increasing, only the rate of autism diagnoses, as greater awareness
of the syndrome and increased screening of children yields more positive diagnoses of autism.

Brainstorming on hypothesis 1 to find the reasons for increased cases of autism and increased awareness among parents evident from the rise in literacy rates, media exposure and campaigns run by the government probably led to hypothesis 2.

There are periods or years when the use of thimerosal vaccines was removed nationwide in several countries including the USA (1992-2000). Studying random populations born from two different periods, say 1992-1997 (when the use of thimerosal vaccines was prohibited) and 2005-2010 (when they were in use) can help draw the correlation between the vaccine and autism.