A doctor assigns people to treatment groups based on data from their medical records. Is this method of selecting treatment groups biased or unbiased?

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  biased

Step-by-step explanation:

Any time a selection criterion is used that is other than a random draw, the selection is biased.

For a medical study, the bias may be intentional. The study may have the purpose of determining treatment efficacy based on age, gender, or previous medical history.

A) The sum is 25 × 26

Step-by-step explanation:

In the attached table we notice a pattern.

For the first positive pair number the sum is

For the first two positive pairs, the sum is

For the first three positive pairs, the sum is .

So:

For the first number of positive pairs, the sum of them is:

If , and then, the sum of the first 25 positive even numbers is:

The correct answer is option A