![]() The z-score is obtained by taking the difference between the data point and the mean, and dividing it by the standard deviation.Ī: Z-scores are useful because they allow us to compare data points from different datasets that have different scales and units of measurement. George did better than 150 students.Ī: A z-score is a statistical measure that tells us how many standard deviations a data point is from the mean of a dataset. This means that almost 75% of the students scored lower than George and only 25% scored higher. Multiply this number by 100 to get percentages. Then go to the x axis to find the second decimal number (0.07 in this case). Find the first two digits on the y axis (0.6 in our example). For George’s example we need to use the 2nd table as his test result corresponds to a positive z-score of 0.67.įinding a corresponding probability is fairly easy. If a z-score calculation yields a negative standardized score refer to the 1st table, when positive used the 2nd table. If you noticed there are two z-tables with negative and positive values. standard normal distribution table) comes handy. ![]() Now, in order to figure out how well George did on the test we need to determine the percentage of his peers who go higher and lower scores. ![]()
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