To find the probability of LARGER z-score, which is the probability of observing a value greater than x (the area under the curve to the RIGHT of x), type: =1 - NORMSDIST (and input the z-score you calculated). Then, to calculate the probability for a SMALLER z-score, which is the probability of observing a value less than x (the area under the curve to the LEFT of x), type the following into a blank cell: = NORMSDIST( and input the z-score you calculated). To make things easier, instead of writing the mean and SD values in the formula you could use the cell values corresponding to these values. Now to calculate the z-score type the following formula in an empty cell: = (x – mean) /. For example, if the range of scores in your sample begin at cell A1 and end at cell A20, the formula = STDEV.S (A1:A20) returns the standard deviation of those numbers. Next, you mush calculate the standard deviation of the sample by using the STDEV.S formula. To calculate the z-score of a specific value, x, first you must calculate the mean of the sample by using the AVERAGE formula.įor example, if the range of scores in your sample begin at cell A1 and end at cell A20, the formula =AVERAGE(A1:A20) returns the average of those numbers. If there is less than a 5% chance of a raw score being selected randomly, then this is a statistically significant result. The probability of randomly selecting a score between -1.96 and +1.96 standard deviations from the mean is 95% (see Fig. Proportion of a standard normal distribution (SND) in percentages. For example, there is a 68% probability of randomly selecting a score between -1 and +1 standard deviations from the mean (see Fig. For example, there is a 68 probability of randomly selecting a score between -1 and +1 standard deviations from the mean (see Fig. Z-Score, also known as the standard score, indicates how many standard deviations an entity is, from the mean. The SND allows researchers to calculate the probability of randomly obtaining a score from the distribution (i.e. The SND allows researchers to calculate the probability of randomly obtaining a score from the distribution (i.e. A standard normal table (also called the unit normal table or z-score table) is a mathematical table for the values of, indicating the values of the cumulative distribution function of the normal distribution. As z-value increases, the normal table value also increases. The table value for Z is the value of the cumulative normal distribution at z. Therefore, one standard deviation of the raw score (whatever raw value this is) converts into 1 z-score unit. Z is the standard normal random variable.