Jun 24, 2011
What is meant by this terminology? [95% confidence interval (-2.1;6.1)]what doses this three number means?
Response from Dr. Young
Hi and thanks for your post.
While frequently confusing, a practical understanding of statistics is an important aspect in understanding clinical trial results.
Typically, what you're referring to is the statistics of a measurement of a hazard ratio (HR, or the relative size of the effect of one factor on another. You've not listed the so-called "point estimate" of the effect, but for example, a HR of 1 means that there is no effect. A HR less than one means that when the factor is present, the risk is less than 1, a HR greater than 1 means that the factor increases the likelihood of the event to occur.
The confidence interval (arbitrarily chosen by convention, at 95%) means that if the experiment or measurement were done 100 times, 95 times, the measured value would occur between the two other numbers (the ones that are reported in the brackets). In your example, the confidence intervals indicate that 95 times out of 100, the estimated HR would be between -2 and 6. Here the values span the value of 1, indicating that the statistical test fails to show a relationship.
Let's look at an example of our recent published analysis of fractures among persons living with HIV. In our analysis, we found that among patients whose lowest CD4+ cell count was below <200, the hazard ratio for fracture was 1.60. This means that when compared to others, patients with CD4 <200 were 1.6 times more likely to experience a fracture. The result is statistically significant, since the 95% confidence interval (reported as 1.11-2.31) was entirely greater than 1.
I hope that helps. BY
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