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What is the z-score of 650?
Example: Find the z-score or z value of a normal variable whose value is 650 if its mean is 500 and standard deviation is 100. The value of the random variable is x = 650, and , , which means that x = 650 is 1 ½ standard deviations above the mean since the z-value is positive. So z = 1.5.
How many standard deviations from the mean is 68%?
one standard deviation
The Empirical Rule states that 99.7% of data observed following a normal distribution lies within 3 standard deviations of the mean. Under this rule, 68% of the data falls within one standard deviation, 95% percent within two standard deviations, and 99.7% within three standard deviations from the mean.
How many points is 1.5 standard deviations below the mean?
| Standard Deviation/Standard/Scaled Score Correspondence | ||
|---|---|---|
| Standard Deviation (SD) | Standard Score | Scaled Score |
| 1 SD below mean | Between 70 and 85 | Between 4 and 7 |
| 1.5 SD below mean | 77.5 | 5.5 |
| 2 SD below mean | 70 or below | 4 or below |
How would you find the percentage of scores that fall between a z-score and the mean quizlet?
Calculate the % above a positive z score: Below the mean means you subtract the percentage between the mean and the positive z score from 50%. Add the percentage between the mean and the z score to 50% (the percentage of scores above the mean) to get the percentage above the mean.
How many standard deviations is 90?
We can use the standard deviation for the sample if we have enough observations (at least n=30, hopefully more). Using our example: number of observations n = 40….Calculating the Confidence Interval.
| Confidence Interval | Z |
|---|---|
| 85% | 1.440 |
| 90% | 1.645 |
| 95% | 1.960 |
| 99% | 2.576 |
What value is 2.5 standard deviations below the mean?
For example, a Z of -2.5 represents a value 2.5 standard deviations below the mean. The area below Z is 0.0062.
What is 2 standard deviations below the mean?
A score that is two Standard Deviations below the Mean is at or close to the 2nd percentile (PR =2). Assume for a moment your child earned a score that is one Standard Deviation below the Mean (-1 SD).