The circles indicate the measured ratio of the number of breast cancers diagnosed in the left breast as compared to the right breast.

<p>The error bars indicate 95% confidence intervals. The solid line is the best fit to a linear model. The best fit slope was −0.0012 (95% confidence interval 0.0104, 0.0042) ratio units per year. The probability that this slope would occur by chance, given that the actual slope is 0, is 0.000008, about one chance in 100,000.