Question

Four risk differences and their 95% confidence intervals are shown below. Which of these is the most precise?

A. -0.15 (-0.45, 0.15)

B. -0.15 (-0.17, -0.13)

C. -0.15 (-0.33, 0.03)

D. -0.15 (-0.25, -0.05)

Answer 1

Here , we are given four risk differences and their 95% confidence intervals are shown below.

Using the given information, we have to tell which of these is the most precise.

Here, notice that, our risk Difference is -0.15

Now, a precise Confidence Interval is the one, which will be of minimum width and which will contain the risk Difference value at its center.

The reason for containing value of the risk Difference at the center is that it will show us that our confidence interval is ( Risk Difference Standard Error )

Which means that, our Risk Difference will be it's Point Estimate.

So, checking the given four alternatives.

A. -0.15 (-0.45, 0.15)

B. -0.15 (-0.17, -0.13)

C. -0.15 (-0.33, 0.03)

D. -0.15 (-0.25, -0.05)

We find that, B. -0.15 (-0.17, -0.13) has the minimum width of [-0.13 -(-0.17)]= 0.04 and the risk Difference -0.15 lies at the center i.e. ( -0.15 - 0.02 , -0.15 + 0.02 ) = ( -0.17 , -0.13 )

Hence, Option B. -0.15 (-0.17, -0.13) is the correct alternative.

This answers your question.

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