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Dr Power and his team drew their data from a study of twins in Australia which had asked relevant questions. The first part of their analysis did not depend on the participants being twins. They looked at 2,082 unrelated individuals aged between 23 and 39 who had been questioned by the study’s organisers about their alcohol and illicit-drug use, who had no symptoms of schizophrenia and who had also given blood samples. Specifically, these volunteers had been asked whether they had ever used cannabis, how old they were when they first tried it and how many times in their life they had taken it. Dr Power and his team then analysed the blood samples for genetic markers associated with schizophrenia.
They learned from the interview data that 1,011 members of the sample had taken cannabis, that the average age at which they had started was 20 and that the average number of times they had taken it was 63. The blood analysis let them calculate, from the number of genetic markers each participant had, and the strength of the association each marker had with the development of schizophrenia, a value called the polygenetic-risk score. This ranged from a low of -0.3 to a high of +0.3, values which correspond to a 50% lower-than-average genetic risk of developing the condition and a 50% higher-than-average risk respectively.
From this part of the study the team found two things. One was a correlation between a participant’s risk score and whether he or she had ever taken cannabis. The other was an association between the amount of someone’s cannabis use and those genetic markers most associated with schizophrenia.
http://www.economist.com/news/scienc...ion-puff-logic
They learned from the interview data that 1,011 members of the sample had taken cannabis, that the average age at which they had started was 20 and that the average number of times they had taken it was 63. The blood analysis let them calculate, from the number of genetic markers each participant had, and the strength of the association each marker had with the development of schizophrenia, a value called the polygenetic-risk score. This ranged from a low of -0.3 to a high of +0.3, values which correspond to a 50% lower-than-average genetic risk of developing the condition and a 50% higher-than-average risk respectively.
From this part of the study the team found two things. One was a correlation between a participant’s risk score and whether he or she had ever taken cannabis. The other was an association between the amount of someone’s cannabis use and those genetic markers most associated with schizophrenia.
http://www.economist.com/news/scienc...ion-puff-logic