Parents of autistic children are in a unique position. They have a unique ability to observe the onset and progression of autism, having a daily and moment to moment interaction with their child. They feel unique pressures and emotions as they interact with their autistic child, such as guilt and love and fear and embarrassment. They are likely to be have unique biases as a result of these unique circumstances.

Recall Bias

Recall bias involves a person’s perception about something occurring in the past being affected by their memory of the event, which memory could have been laid down incorrectly at the time, or changed over time due to intervening circumstances or information. Rarely are memories about past events totally accurate. Memories fade and change over time. This is also true of the memories of parents of autistic children. When parents look back after a child has been diagnosed with autism, they often remember the world in a distorted way.

One of the strongest pieces of evidence in the mind of many that vaccines cause autism is the temporal association between the administration of vaccines, particularly the first MMR shot typically given around 14-18 months of age, and the onset of / regression into autism. Rarely do parents of children with regressive autism remember facts or events that indicate that the child showed evidence of autistic traits before the vaccination / regression occurred (some evidence the vaccine did not cause the autism – it is typical for parents to remember their baby having been perfect before this happened. This is part of the reason why the regression can be so shocking.

However, it is very clear that autistic traits are recognizable by experts in many regressive autistic children (who regress over a year later) as early as 4 to 6 months of age. This has been shown in many studies. For instance, an expert group convened by the Medicines Control Agency in Britain reviewed the records of 92 children with autism whose parents thought that MMR had caused or triggered their child’s condition. In 36, there was evidence in the medical records that there had been concerns about the child’s behaviors before the MMR vaccination (and these are only the cases that made it into the medical records). However, in only one of these cases, did the parent recall the early concern.

Numerous researchers have conducted home video studies showing autistic behaviors in regressive autistics before the vaccine ‘trigger’. In one study, over 50 percent of the children who experienced a regression demonstrated some early social deficits during the first year of life, long before regression and the apparent onset of autism. In another study of children who developed regressive autism, all 17 of the children showed movement abnormalities as early as 4 to 6 months of age. Other studies have shown similar findings. 

Attribution of Cause

One large factor in the spread of the vaccine theory of autism relates to parental attribution of the cause of their child’s autism. Outside influences are affecting the attributions parents make about the cause of autism. And, these influences are probably causing them to make inaccurate attributions. These influences are creating biases in the parents that are being transmitted to society generally.

For instance, parental attribution of a specific cause, or at least a trigger, is very prevalent in autism, particularly regressive autism. Davidovitch et al examined maternal perceptions in autism. They found that where children with autism had developmental regression, almost all mothers attributed specific causes their child’s autism, compared to only two thirds of others whose children did not show regression. The presence of the regression is causing parents to alter their perception of past events, likely to search for temporally connected events and tie the events and the regression together in their heads.

We have also seen that the attributions that parents are making have changed in the last 10 or so years. Before 1997, parents incriminated trigger factors such as domestic stress, seizures, or viral illness. Post-1997, parents were more likely to attribute regression to vaccination, especially the MMR vaccine. Widespread public concern about the possible relation between autism and MMR began in August 1997, with the pre-publication release of information about the Wakefield study. Lingam et al found that MMR was reported as the trigger of autism in 6 of 30 (20%) of cases post-August, 1997 compared with 2 of 46 before August, 1997. They also found that not only did the rate of attribution of regression to the MMR vaccine change post-Wakefield, but some parents apparently changed their story as well.