Brain tumour risk and Mobile phone use
November 7, 2010. A very important paper by Lennart Hardell, one of the leading scientists doing research on the link between mobile phones and brain tumours, was recently published in the European Journal of Oncology.
In a recent email I was asked to explain what OR and CI mean so the lay person can interpret the results in the abstract.
You can get the abstract here that also contains a table based on data from the text and my comments.
Briefly the OR is the odds ratio and the CI is the confidence interval.
The odds ratio (OR) is the ratio of the observed over the expected outcome. If the value is above one it means there is a greater risk for mobile phone users (as in this study) and a particular outcome, such as a tumour. If the value is below one there is a reduced risk of that outcome. An odds ratio value of 2 means a two-fold increase or 100% increase in risk. An OR of 4 means a four-fold increase or a 300% increase in risk of developing a brain tumour.
The 95% confidence interval (CI) is used to determine if that odds ratio is statistically significant. If the CI remains above one for an OR that is above one, then the OR is statistically significant and scientists have 95% confidence that the result is not due to chance.
Latency period is the time between first use of mobile phones and a detected outcome, like a brain tumour. Generally the studies are finding a statistically significant increased risk after a 10-year latency period. This is quite rapid for brain tumours that normally have a latency period of 20 to 30 years in adults.
What the Hardell study documents is that for those who started using a cell phone before the age of 20 years their risk of developing a brain tumour is detected after a latency period of more than 1 year and the is risk high (OR 5.2) and is statistically significant (95% CI 2.2-12).
Another important result is that risk for developing tumours is much higher for ipsilateral than for contralateral tumours. An ipsilateral tumour is on the same side of the head where one holds a mobile phones while contralateral refers to the other side of the head. Brain cells are exposed to higher levels of microwave radiation on the ipsilateral side than on the contralateral side and this is where most of the tumours are detected.