MATH 1F92 Lecture 8: Math+1F92-+7.2b-+Finding+Z-scores+and+percentiles+fill+in
16 Feb 2017
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7. 2b- finding z-scores and percentiles of the standard normal. Sometimes, rather than finding the probability of our random variable being between two values, we prefer to find the actual raw score that is associated to a certain percentage. Percentile rank: describes what percentage of scores are beneath the given percentile. On a standard normal curve, we can actually write a z-score in terms of its percentile in the following format: represents the z-score that has (cid:515)alpha(cid:516) proportion/probability of values up to that point. (cid:2868). (cid:2868)5. 5% of the values are below this z-score- 95% of the values are below this z- scores (cid:2868). (cid:2877)5. To find a z-score using the z-table, we are essentially doing the reverse steps of what we did to find the probability under the curve. Steps: using the left tailed z-table, search for the probability that is closest to . If there are two that are equally close, either one is acceptable.
