Read the sentence, looking for clues
The key phrase "to ensure accurate results" gives a clue to the word for the first blank. The word will be an adjective describing the kind of evidence the scientists wanted to rely on. For the second blank, the word will describe the kinds of practices in data collection that could "render the experiment useless." The clue for the final blank is the fact that the experiment could be rendered "useless." That would suggest something very bad happening to "the precision of the outcome."

Predict the answers
For the first blank, the scientists would want to rely on "concrete," observable evidence in order to ensure accurate results. For the second blank, it can be predicted that "sloppy" or "inexact" practices in data collection could be a major problem. A good prediction for the third blank might be that those sloppy practices could "negatively affect" or "put in doubt" the precision of the outcome.

Select the best matches from among the choices
(A) empirical, or "based on observation," while not an exact match for the prediction, is related to it and is the correct choice. (B) historic means "established in the past." There is no reason to connect historic evidence with ensuring accurate results, so this choice can be eliminated. (C) dilatory means "slow, tending to delay," which makes no sense in the context of the sentence.

For the second blank, (F) anomalous, which means "inconsistent" or "irregular," matches the prediction and is the correct choice. (D) stringent, which means "strict" or "rigorous," might describe practices that would help the experiment. So this choice is the opposite of what is needed here. (E) outlandish, or "bizarre," is too strong. It might be true that bizarre practices would be a problem, but nothing in the passage suggests such an extreme word is called for here.

The third blank's correct answer is (H) seriously jeopardize, which means to "imperil" and matches the prediction. (I) positively impact is too positive in tone. (G) adversely promote contains the negatively charged adverb "adversely," but "promote" is too positive, so this choice is also incorrect.

Confirm your answers by reading them into the sentence
Wanting to rely entirely on empirical evidence to ensure accurate results, the scientists drafted strict guidelines for observing the progress of the experiment. Any anomalous practices in data collection could seriously jeopardize the precision of the outcome, rendering the experiment useless.

TAKEAWAY: If it sounds like a multiple-word answer would be the best fit for a blank, take a quick glance at the choices to see if that is what is expected.