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Immunisation 2/2

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 CorrelationWhen things happen at the same time e.g. when two variables change simultaneously.  CausationWhen changes in one variable cause a change in another.

 Ice cream sales don’t cause people to drown.  Drowning people don’t cause ice cream sales to go up.  Instead, both variables are affected by a third – how nice the conditions are at the beach. There is correlation but not causation.

Ideally scientists  change an _________ variable  measure (resulting) changes in the _________  and keep all the _________ variables the same.

Ideally scientists  change an independent variable  measure (resulting) changes in the dependent  and keep all the control variables the same.  Why would this be difficult when investigating possible causes of medical conditions in real people?

 Data is available for the number of mobile phone masts in an area and the number of babies born in any given year.  Choose an appropriate graph and use the data provided to see if you can find a link.  Can you explain it?

 In 1998 a UK doctor, Andrew Wakefield, was one of 13 authors of a paper suggesting that there was evidence linking the MMR vaccination given to young children and the development of autism, associated with unusual bowel conditions.  What questions would you want to ask about the findings and methods of the paper?

 Study was very small – only 12 children.  Soon after publication questions were raised about contamination of the bowel samples.  In several cases children had taken part in the study because their parents already believed there was a link.  Further observations were planned, comparing children who had received the vaccination and those who had not.

 Causes for medical conditions and links between symptoms are suggested all the time. We call any suggested link between variables a hypothesis.  The problem was that newspapers and TV stations, first in Britain then worldwide, published the possibility of a link as a fact – without any discussion of other possible explanations, or the limitations of the study.

What do you expect happened to:  The vaccination rate for MMR?  The overall vaccination rate?  The number of parents to autistic children who believed it was linked to MMR?  The number of cases of measles, mumps and rubella?

 It is 1998 and some parents have suggested cancelling the MMR vaccination programme.  You have been asked to write a short paragraph explaining to them why this would be an over-reaction.  Use what you know about the risks of measles, mumps and rubella.