How can I calculate the z score on my casio fx-115ES plus calculator? I need to know for statistics. This p-value calculator helps you to quickly and easily calculate the right-tailed, left-tailed, or two-tailed p-values for a given z-score. Ask Question Another workaround I can think of is to go to your Results pane and find a working Calculate Field result. For each problem below draw a picture of the normal curve and shade the area you have to ﬁnd. Includes Weight-for-age, Stature-for-age, Weight-for-stature, and BMI-for-age Support PediTools. X = The value to be standardized. In that case the t-value is given for 3000 degrees of freedom. To clarify what I need: I have two different models that have been generated by splitting the sample. The table shows the area from 0 to Z. , for an RM ANOVA or Mixed ANOVA), unit-weighted scores should be used. The calculator will then give you an answer, and guide you through a solution so you can learn to solve this problem on your own. You want to be on the screen where you can enter data into a list. Find the Z score for 80. # # In this example, Calculator is initialized with its default values # (i. But why? Let's look at the equations: A z score is the same as a standard score; the number of standard deviations above the mean. We can now see that the sample standard deviation is larger than the standard deviation for the data. Thus from the empirical rule we expect 99. The z-value calculation is based on algorithm 209 from the CACM by D. Also it may be useful for to use our z score area calculator. 445200708300442 = 44. com is an independent, advertising-supported publisher and comparison service. The approximate is always used. Data is from 782 patients evaluated at the Children's Hospital of Michigan. 3 Homework Answers 1. The best method of checking normality is to plot a histogram: if the distribution is relatively bell shaped (i. Use this Z to P calculator to easily convert Z-scores to P-values (one or two-tailed) and see if a result is statistically significant. graph lumped high in the middle and tailing at either end) and doesn't extend to a greater extent on one side than on the other, proceed with parametric stats. Probability calculation using the Z score. The first step to find the z-score is to find the population mean and standard deviation. Parenteral nutrition calculations Enter fluid volume, dextrose, and goals for amino acids and lipids, and will calculate PN composition, GIR, and estimated osmolarity. In the HEART Score study, these patients were candidates for early invasive measures. These are the so -called Z -Score model (1968) and ZETA ® 1977) credit risk model. How To Calculate Z-Score Normalization - A Calculation - (Data Mining) In this tutorial, we will learn about the Z score normalization. The Z-Score is a commonly used metric with wide appeal, though it is just one of many credit scoring models in use today that essentially combine quantifiable financial indicators with a small number of variables in an attempt to predict whether a firm will fail. This calculator determines the area under the standard normal curve given z-Score values. The M-Score is calculated as in Beneish, Lee Nichols 2013, Financial Analysts Journal. 7 - Finding Probabilities using a. In statistics, the z-score (or standard score) of an observation is the number of standard deviations that it is above or below the population mean. Calculate Z Score and probability using SPSS and Excel In statistical inference, we are interested to know whether a small sample comes from a population. Selecting two-sided provides the area above Z and below -Z. It's the app that has an icon of a green sheet with an "X" in front 2. Example Excercise: Calculate the population standard deviation or dispersion of entire population 165. 0401 < α = 0. The raw score computed is the actual score, or value, obtained. To clarify what I need: I have two different models that have been generated by splitting the sample. Because of symmetry reasons (the standardized normal distribution is symmetric around 0) the z score that corresponds to the upper portion is equal to —z or —1. The calculator will return Student T Values for one tail (right) and two tailed probabilities. For example, if 1 year-old child had a PFL = 20 mm, that child's PFL would be 1. Using the Z-score to find the cheapest trusts. The sign of the score indicates whether it is above (positive) or below (negative) the mean, and the value quantifies how many standard deviations the score is from the mean. The lower Z-scores of each members of population collectively improves the standard deviation of the distribution and so the uncertainty of expected results become low. In addition it provide a graph of the curve with shaded and filled area. Whether your goal is to earn a scholarship, get into a prestigious college, or ensure you will graduate, when it comes to figuring out your high school GPA, we’ve got you covered. For an explanation of the program that produces this output, see Standardizing BY Groups and Replacing Missing Values. In other cases, you may have the data set and the specific value for which you need to calculate the z-score. If an individual scores 72 on Test A and 84 on Test B, which did he do better on?. In Excel 2007 and above, the syntax is NORM. The calculator computes the M-Score, the odds ratio that the firm is a manipulator, and provides an assessment based on whether the model's variables are out of line relative to sample averages. From the stated hypothesis, we know that we are dealing with a 1-tailed hypothesis test. 2 Z-Score Practice Worksheet. 96, you are 95% confident that that Variant Recipe is different than the Control Recipe. Everything. 08 and the standard deviation was 3. Scores 4-6: 12-16. To calculate the probability of getting a value with a z-score between two other z-scores, you can either use a reference table to look up the value for both scores and subtract them to find the difference, or you can use technology. Calculates the z score of each value in the sample, relative to the sample mean and standard deviation. The absolute value of z represents the distance between the raw score and the population mean in units of the standard deviation. Z-score: p-value: p-value type: right tail two tails CANVAS NOT SUPPORTED IN THIS BROWSER!. If axis is equal to None, the array is first raveled. 98521 which is the lowest Z score value of Adrian Steve who has achieved the lowest score in the exam. Get an answer for 'Cutoffs:Find the corresponding Z score(s). The Z score Calculator an online tool which shows Z score for the given input. Z score calculation is normally conducted to find out where our value lies in respect to the mean in a normal distribution. Practically speaking, Ppk can be determined by dividing the Z score by three. Z-Score Definition: A z-score value is measurement in Statistics which indicates a given score’s relationship to the mean. Cp and Cpk Process Capability Metrics; Pp and Ppk Process Performance Metrics. The calculator uses the provided information, and calculates the Z-score based on the patients age, gender, IGF-1 result, and the appropriate Endocrine Sciences reference interval. A score of 80, where the mean score of the sample data values is 30. Now Joestat wants to help you find the probabilities of a given z-score using the following examples. x may or may not be a part of the data set. 68-95 rule It is readily calculated that 68% (. It shows you the percent of population: between 0 and Z (option "0 to Z") less than Z (option "Up to Z") greater than Z (option "Z onwards") It only display values to 0. That means that the area to the left of the opposite of your z-score is equal to 0. The Basic Z Score Formula The basic z score formula for a sample is: z = (x – μ) / σ This is a formula that assumes a normal distribution for the z score is possible. You could use the equation above to find the z-score; with a little arithmetic, you can look up a critical value in a z-table, or you can use the InvNorm function on the TI-83 graphing calculator. 645 Any z-score to the left of -1. The upper value corresponds to 1 – 0. Enter how many in the sample, the mean and standard deviation, choose a confidence level, and the calculation is done live. Is this a foolproof way of spotting bargains? 09 February 2017 |Investment Trusts. 77% of bottleneck. The data value x exists in two data sets: A and B. What is a Z-score? A Z-score, also known as a standard score, represents the number of standard deviations (SDs) a data point is away from the average (mean) of the group. Different methods are used for aortic root dilatation in different publications (eg. This second calculator allows you to calculate the z-score for any given cummulative probability level (simply put, for any given value of p). A defect happens when a product’s quality characteristic such as color, weight, size is not in conformance to the product’s specification. To do this, I will use an example, as mentioned previously. 5201% Cumulative This gives you the probability of the area below the Z Score. A simple calculator that generates a P Value from a z score. A z-score can be calculated from the following formula. One should take into account these differences when choosing a formula to calculate Z-scores. 05 significance level is roughtly 1. Z-scores, therefore, are a useful way of standardising values. If not, you can do the calculation manually in a data step. Press Ctrl+D, which copies the formula in the top cell down through all the other selected cells. For an explanation of the program that produces this output, see Standardizing BY Groups and Replacing Missing Values. Individual values may be separated by commas, spaces, tabs od new-line. We first look at how to calculate the p value using the Z-score. Using z-score I need to select and flag the records as follows: 1. 72% of bottleneck. If you have the WHO Anthro package you can use their anthropometric calculator to calculate Z-scores (and percentiles assuming a normal distribution) with the new WHO reference values. The z-score is also used to standardize data prior to analysis, calculate the probability of a score or comparison of two or more data points which are from different normal distributions. What does this actually mean??? By calculating Z-scores for your data, you can compare your figures to a normal distribution curve (you know, the bell shaped diagram you learnt in school above). Z-scores are useful for analyzing numbers in the context of the rest of the field. The z-score is the number of standard deviations away from the average value of the reference group. The formula to calculate z-score is. 96, or greater than 1. DPMO is a measure of process performance. It has a reported 72% accuracy in predicting bankruptcies two years in advance. Parenteral nutrition calculations Enter fluid volume, dextrose, and goals for amino acids and lipids, and will calculate PN composition, GIR, and estimated osmolarity. A z-score can be calculated from the following formula. Online tools and calculators for biology, bioinformatics, statistics, and medical statistics. How to Calculate a Z-Score Z-Score Formula. Remember that the z-score tells you how many standard deviations away from the mean a particular point lies. The Z-score scale is linear and therefore a fixed interval of Z-scores has a fixed height difference in cm, or weight difference in kg, for all children of the same age. The values presented in the graphs above are approximations derived from the work of Abramowitz & Stegun. No matter if you are in a hurry to get your z score or if you are only trying to check if you did all the calculations right, having a z score calculator in the nearby is always a good option. This means that the remaining probability is 0. Using the Z-score to find the cheapest trusts. Click the button below to go to the Adobe website and download it. For more videos please. Of course, the job of interpreting what the z score means still falls to your shoulders, but at least you don't have to make your head ache by hand-writing and calculating the z score formula. Since we are interested in the positive value, we conclude BUT, there is a MUCH EASIER way to find these values using StatCrunch… Example 1: Find the following z-scores:. That is also going to be -0. IQ scores have a mean of 100 and a standard deviation of 16. A z-score can be calculated from the following formula. Press Ctrl+D, which copies the formula in the top cell down through all the other selected cells. 645 will be rejected. 6 Z score is displayed here:. It will give the second column the same name as the first column with a letter 'z' in front of it. 5 Value of z exactly at the middle is 0 We have to find the area for 95% or 0. z is negative when the raw score is below the mean, positive when above. EUROSCORE INTERACTIVE CALCULATOR: STANDARD AND LOGISTIC REGRESSION - European System for Cardiac Operative Risk Evaluation (EuroScore) VERY VERY EXTENSIVE. Often it can be useful to transform your raw scores into Z-scores. The formula for converting raw scores on any interval or ratio variable X to z scores is:, where: z i is the standard score for case i, X i is the raw score for case i, μ is the mean of the variable, and. 1 Computing the test statistic and p-value We’ll use SAS to perform the calculations for Exercise 6. A z-score that is greater than 4 is usually reserved for the elite outliers in a statistical category. For example, a test score that is greater than 75% of the scores of people taking the test is said to be at the 75th percentile, where 75 is the percentile rank. Stat 1010 - critical values Critical Values for Statistical Significance ! Significance level of 0. The raw score computed is the actual score, or value, obtained. Also, Z score is one of the most accurate credit models because a change in a firm’s score suggests that, most likely, the firm’s fundamentals have changed. Two P values are calculated in the output of this test. Using the z table calculate the following percentage for z score of -0. 05, then reject the null hypothesis and conclude the distribution of the sample is non-normal. Is your company heading towards bankruptcy? The Z-Score, developed by Dr. Find the z-scores corresponding to each of the following values: A score of 60, where the mean score of the sample data values is 40. “Z-scores were computed for raw scores in the grades data set. It will give the second column the same name as the first column with a letter 'z' in front of it. A z-score less than 0 represents an element less than the mean. It takes 3. Within SPSS the. qThe Z -score is expresses the number of standard deviations the value x is from the mean qA negative Z -score implies that x is to the left of the mean and a positive Z -score implies that x is to the right of the mean Z Score Equation z = x - x s For a score of 83 from the aptitude data set, z = = 1. Calculate the mean and standard deviation. If you want to calculate the z score based on the raw score, mean, and standard deviation, see Z Score Calculator. This calculator determines the area under the standard normal curve given z-Score values. The z-score, also known as standard score, is a measurement used in statistics. (2016, 2017, german longitudinal data) New LV strain z-scores for echocardiography according to Dallaire et al. 5% in the upper tail and 3. What is a Z-score? A Z-score, also known as a standard score, represents the number of standard deviations (SDs) a data point is away from the average (mean) of the group. Given α = 0. Just enter your p -value, which must be between 0 and 1, and then hit the button below. 08, and 167. Read and learn for free about the following article: Z-scores review If you're seeing this message, it means we're having trouble loading external resources on our website. Z Table Score Calculator allows you to quickly calculate z-scores. Whether you specify that the data is from a population or a sample will not affect the result. Two P values are calculated in the output of this test. In statistics, the z-score (or standard score) of an observation is the number of standard deviations that it is above or below the population mean. This calculator can calculate Z scores using a formula by Kobayashi et al. 05, then reject the null hypothesis and conclude the distribution of the sample is non-normal. In the programs I used to calculate grades for my students I standardize each student's average (across exams etc. You can calculate standard deviations easily, or get a spreadsheet to do it for you. Page 1 of 1 of C:\data\StatPrimer\z-two-tails. It is also known as a z-score. 44 % of the students are within the test scores of 85 and hence the percentage of students who are above the test scores of 85 = (100-89. We can now see that the sample standard deviation is larger than the standard deviation for the data. It shows us that the score is equal to the mean, below the mean or above the mean. You can use AVERAGE and STDEV. 645 Any z-score to the left of -1. We want to compare x to a data set (or population) with mean (or μ) and standard deviation s (or σ). 68-95 rule It is readily calculated that 68% (. The z score is the numerical value which represents how many standard deviations a score is above the mean. The z score for an item, indicates how far and in what direction, that item deviates from its distribution's mean, expressed in units of its distribution's standard deviation. You can apply the Cumulative Distribution Function (CDF) to calculate the probability of various outcomes, and use this information to make appropriate business decisions. If Z-score equals 1, the safety stock will protect against one standard deviation; there will be enough inventory 84 percent of the. You can use ZTEST or Z. zscore¶ scipy. Use our ONLINE CALCULATOR to calculate the ALTMAN Z'-SCORE for PRIVATE FIRMS. Simple Z Score Calculator. And the Z-score for this data point is going to be the same. The monthly utility bills in a city have a mean of $70 and a standard deviation of $8. Using a simple formula, you can easily determine the p-value for your tests and thereby conclude strong or weak support of the null hypothesis. Z-scores base this information on data distribution and using the standard deviation measurements of data to calculate outlier under the understanding that about 68% of measurements will be within one standard deviation of the mean and about 95% of measurements will be within two standard deviations of the mean. If you have your standardized z-score, this calculator will help you convert that to a confidence level for either one-sided or two-sided tests. Returns the one-tailed P-value of a z-test. This computation assumes that the number of successes and sample measurements is large enough (normal approximation is used). Using z-Scores to Find Normal Probabilities or Random Variable x Values: If we’re given a value x and need to nd a probability, convert x to a z-score using z = x ˙; use a table of normal probabilities (or software, or a calculator) to get a cumulative probability, and then convert it to the probability of interest. Enter a value, population mean and the standard deviation (for the population). First, enter values for the mean, standard deviation, and data value. Step 1: Write your X-value into the z-score equation. even so, there will be enough inventory to meet demand in 50 percent of cycles. A Z score can be determined by multiplying the Ppk score by 3. From the stated hypothesis, we know that we are dealing with a 1-tailed hypothesis test. Unless otherwise stated, we can assume an alpha level of 0. To inference using sample mean, when the population standard deviation and population mean are known , we can use Z test to interference the population mean from sample mean. Easy to use calculator for converting a P-value to a Z score using the inverse cumulative probability density function (cumulative PDF) of the normal distribution. These are the so -called Z -Score model (1968) and ZETA ® 1977) credit risk model. It will generate the p-value for that Z-statistic. How to Calculate a Z-Score Z-Score Formula. 5 to 20 years of age. WorldCom Test. Calculate the mean and standard deviation. We're told to assume that the scores are a random sample from the third graders in a suburban school. It is the measurement of the number of standard deviations a specific number is above or below a mean. This Z Score calculator finds the Z score by considering a given raw score value, the mean and the standard deviation of the population to which the raw score (standardized random value) belongs. calculate standardized values using a given mean and standard deviation print the data set with the standardized values. If you need precision to more that 6 decimals you are encouraged to consult multiple published tables of Z-Values. A z score table is used in hypothesis testing to check proportions and the difference between two means. 9332 is the proportion in the population above a z-score of -1. The suggested results are not a substitute for clinical judgment. Uses the 2000 CDC Reference for triceps and subscapular skinfold-for-age, to report percentiles and Z-scores on children from 1. In order to calculate the z-score, James first needs to calculate the mean and standard. 39 of the text. * The PFL z-score reflects how many standard deviations (SDs) the patient's PFL is above or below the normal population mean. The ratios rely on the following financial measures. It is a Normal Distribution with mean 0 and standard deviation 1. Test function used to calculate the one-tailed probability value of the Z-Test for two different hypothesized sample means. The step-by-step z-score calculator calculates a z-score based on the z-score formula. He would then calculate the p-value. Which statistical distribution a customer satisfaction survey follows ? Can one treat it normally distributed? If yes, is it possible to calculate Z score of this data using LSL = 0 and USL = 100 ? I am not sure, in what format your data is, but if you have measured customer satisfaction in terms of. , a standard normal score), given an unstandardized raw value, the population mean, and the standard deviation of the population to which the unstandardized value belongs. Why this is important in Six Sigma. 5% (a total of 5% represented by 1–0. Click here for older java version of this applet. Users may refer the below table to choose the corresponding Z-score for the different confidence levels. 1-sample z-test for a population proportion: Input Values : Compare a sample proportion with a hypothesised population value. ) or comma (,) as decimal separators. the z-scores before calculating and interpreting the TSA. Enter the mean, standard deviation, and click the "Calculate" button to see the results. Step 1: Write your X-value into the z-score equation. How do I standardize variables in Stata? | Stata FAQ A standardized variable (sometimes called a z-score or a standard score) is a variable that has been rescaled to have a mean of zero and a standard deviation of one. Please do not use this calculator primary as decision maker than as helping tool to understand performance correlations between different components. This zone (shown in green here) is called the Rejection Region. The procedure is not very good for estimating large z-values. print the data set with the standardized values. This table also shows the value for the average minus two and minus three standard deviations. Notice the inequality points to the left. The standard score shows how far away from the mean a score falls. If you look at the equation for calculating Z is it exactly 3 times the formula for a Cp(u or l) if you put the specs in for calculating Z. Get a Z score for normally distributed data using this online calculator. The Wilcox Sign Test in SPSS. Prerequisites. We have spent some time going through the concepts of hypothesis testing. 975, which gives a z ‐value of 1. 8 means it's likely the company is headed for bankruptcy, while companies with scores above 3 are not likely to go bankrupt. Process Capability Metrics You Don't Have to be a Statistician to Understand Process Capability Metrics like Cp and Cpk. X represents the raw score, x_bar is the mean, z is the z-score and s is the standard deviation. 025 in each of the tails. Within SPSS the. 025 p-value. 99 Test scores. Please input degrees of freedom and probability level and then click "CALCULATE". Easy to use calculator for converting a P-value to a Z score using the inverse cumulative probability density function (cumulative PDF) of the normal distribution. For an explanation of the program that produces this output, see Standardizing BY Groups and Replacing Missing Values. Bottom 15% low $$ customers (z-score of the dollar_amt variable less than -1). If you want to calculate the z score based on the raw score, mean, and standard deviation, see Z Score Calculator. P-Value Calculator for Normal Distribution. Body Mass Index (BMI) and Z-Score Calculation in Children Instructions This web page allows you to calculate the body mass index (BMI) of your patients between the ages of 2 and 20 years, as well as the exact BMI percentile and z-score (standard deviation), based on the Center for Disease Control (CDC) growth charts. Contrary to what many people believe, z-scores are not necessarily normally distributed. How to calculate z-score. The values presented in the graphs above are approximations derived from the work of Abramowitz & Stegun. Calculate z from probability Q. PDF | Bone mineral density (BMD) can be measured by a variety of techniques at several skeletal sites. Instructions. The calculator will find the p-value for two-tailed, right-tailed and left-tailed tests from normal, Student's (T-distribution), chi-squared and Fishe P-Value Calculator - eMathHelp eMathHelp works best with JavaScript enabled. How to Calculate a Z-Score Z-Score Formula. qThe Z -score is expresses the number of standard deviations the value x is from the mean qA negative Z -score implies that x is to the left of the mean and a positive Z -score implies that x is to the right of the mean Z Score Equation z = x - x s For a score of 83 from the aptitude data set, z = = 1. To see the connection, find the z*-value that you need for a 95% confidence interval by using. It's free, and only takes a minute to install. How the score for a single letter is calculated is left as a detail for now. Input values should come from DXA instruments made by the Lunar ® or Hologic ® corporations. The calculator will generate a step by step explanation along with the graphic representation of the area you want to find and standard normal tables you need to use. x may or may not be a part of the data set. If an individual scores 72 on Test A and 84 on Test B, which did he do better on?. graph lumped high in the middle and tailing at either end) and doesn't extend to a greater extent on one side than on the other, proceed with parametric stats. 5% in the lower tail. 5 indicates osteoporosis. Examine the table and note that a "Z" score of 0. A z score is defined as the deviate score (the observed score minus the mean) divided by the standard deviation s X - X z = It tells us how far a score is from the mean in units of the standard deviation _____ _____ _____ _____ 6 An Example You have a z score of -1 on the first exam Your score was one standard deviation below the mean on exam 1 ()() 1 5 80 85 s X - X z =− − = = ()() 1 5 75 70 s X-X z = − = =. 025, and a z-score of -3. Press Ctrl+D, which copies the formula in the top cell down through all the other selected cells. zscore¶ scipy. The English scrabble letters have the benefit that they are all contiguous in the Unicode character set. Purpose: The purpose of this program is to calculate z-scores for either sample (i. To see the connection, find the z*-value that you need for a 95% confidence interval by using. Use our Discounted Cash Flow (DCF), Price Implied Expectation, Ben Graham formula, EBIT multiples, Absolute PE, and Earnings Power Value models to triangulate a stock’s intrinsic value. Enter how many in the sample, the mean and standard deviation, choose a confidence level, and the calculation is done live. Thank you very much. Edward Altman who used it predict the likelihood that a company would go bankrupt. The upper value corresponds to 1 – 0. Top 15% high $$ customers (z-score of the dollar_amt variable greater than +1) 2. A normal distribution of scores has a standard deviation of 10. z score value to percentile calculation and formulas. For the biology test, we need to know that the mean was 60 with a standard deviation of 10. For the raw score 98%, z = 1. Parenteral nutrition calculations Enter fluid volume, dextrose, and goals for amino acids and lipids, and will calculate PN composition, GIR, and estimated osmolarity. Weight-for-height percentiles and z-scores are also calculated. So the farther a z score deviates from the mean of zero the more significant, or unusual, it. where z is the z-score, X is the value of the element, μ is the population mean, and σ is the standard deviation. 6% retrospective, 16. This has been a guide to Z Score Formula. Descriptions and formulas for these metrics are described below. Recommended Articles. doc Last printed 4/7/2007 10:47:00 AM Two tails of Z Entries in the table represent two-tailed P values for z statistics. Altman in 1968, is the most widely tested and accepted Bankruptcy predictor in use. The default units are cm and g. The value of 20 has a Z score of 0, which means it is equal to the mean. It's the app that has an icon of a green sheet with an "X" in front 2. The sign of the score indicates whether it is above (positive) or below (negative) the mean, and the value quantifies how many standard deviations the score is from the mean. For math, science, nutrition, history. Please input degrees of freedom and probability level and then click “CALCULATE". The calculator allows area look up with out the use of tables or charts. Cpk = (USL – LSL)/ 6 σ Ppk = (USL – µ) / 3σ. We won't be discussing that in this lesson. We do so by specifying the desired level of conﬁdence using the conf. Normal Distribution Calculations Using Technology All of the calculations that we will do in Math 180A involving the normal distribution can be done using tables. Z-scores base this information on data distribution and using the standard deviation measurements of data to calculate outlier under the understanding that about 68% of measurements will be within one standard deviation of the mean and about 95% of measurements will be within two standard deviations of the mean. The knock about the Z Score is its relative lack of any specific measurable outcomes. Get the free "Z-score Calculator" widget for your website, blog, Wordpress, Blogger, or iGoogle. The z-score, also known as standard score, is a measurement used in statistics. This calculator determines the area under the standard normal curve given z-Score values. 50 or 50%, and a "Z" score of 1, meaning one standard deviation above the mean, lists a probability of 0. It is the measurement of the number of standard deviations a specific number is above or below a mean. You can also use the table below. It is a statistical measurement of a score's relationship to the mean in a group of scores. You'll find that WorldCom's Z-score suffered a sharp fall. z score value to percentile calculation and formulas. Step 1: Write your X-value into the z-score equation. One should take into account these differences when choosing a formula to calculate Z-scores. Thus from the empirical rule we expect 99. The z-scores of 4 and 1 would add to five, for an average z-score of 2. 96 standard deviations.