At the core of biology and other sciences lies a problem-solving approach called the scientific method. 1  Make an observation. 2  Ask a question. 3  Form a hypothesis, or testable explanation. 4  Make a prediction based on the hypothesis.  Test the prediction.
Xi. Xi is the 14th letter of the Greek alphabet. It is pronounced in Modern Greek, and generally or in English. In the system of Greek numerals, it has a value of 60. Xi was derived from the Phoenician letter samekh. Xi is not to be confused with the letter chi, which gave its form to the Latin letter X.
To compute the probability that an observation is within two standard deviations of the mean (small differences due to rounding): This is related to confidence interval as used in statistics: xÌ Â± 2Ï is approximately a 95% confidence interval when xÌ is the average of a sample.n the empirical sciences the so-called three-sigma rule of thumb expresses a conventional heuristic that nearly all values are taken to lie within three standard deviations of the mean, i.e. that it is empirically useful to treat 99.7% probability as near certainty.