STATISTICAL TECHNIQUES AND TOOLS
Z DISTRBUTION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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-5
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-2
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2
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5
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Detailed explanation-1: -z = (x – ) / For example, let’s say you have a test score of 190. The test has a mean () of 150 and a standard deviation () of 25. Assuming a normal distribution, your z score would be: z = (x – ) /
Detailed explanation-2: -If you want to calculate the probability for values falling between ranges of standard scores, calculate the percentile for each z-score and then subtract them. For example, the probability of a z-score between 0.40 and 0.65 equals the difference between the percentiles for z = 0.65 and z = 0.40.
Detailed explanation-3: -Regardless of what a normal distribution looks like or how big or small the standard deviation is, approximately 68 percent of the observations (or 68 percent of the area under the curve) will always fall within two standard deviations (one above and one below) of the mean.