# T Score To Z Score Calculator

The standard normal distribution has been well-studied, and there are tables that provide areas underneath the curve, which we can then use for applications. test(VarA, conf. Standard Score (cont) Z-scores are expressed in terms of standard deviations from their means. If we normalize the data into a simpler form with the help of z score normalization, then it’s very easy to understand by our brains. For example, could you imagine telling the parents of a child that their son (or daughter) has an IQ of -1. For the numbers below find the area between the mean and the z. The formula for transforming Z-score into a T-score is a follows: 50 + 10(z). Since this is a common need, someone has already done the coding for you; however, you may still need to install it. A Z-Score is a score that belongs to a standard normal distribution, where the Mean is 0, and the Standard Deviation is 1. By continuing to use this site you consent to the use of cookies on your device as described in our cookie policy unless you have disabled them. The normal for Z-score. your expression is good. The Standard Normal Model: Standardizing Scores For the purposes of this post, we will refer to the data values in a data set as "scores. For example, given a sample mean of 20, an estimated population mean of 22, a sample standard deviation of 3 and a total of 4 observations, you would have a t score of 2. By convention, values greater than |1. What Do I Do With It? You can then take your t-score, 25. Z-Test Two Sample for Means in Excel QI Macros Add-in for Excel Makes Conducting Z tests a Snap When to use the Z-Test two sample for means. Click here to learn more about the t-distribution and t-tests with examples. The Z-Score Calculator uses the following formula: z = (x - μ) / σ. Although normal distributions may have different means and standard deviations, all normal distributions are "bell-curve" shaped, symmetrical with a peak at the mean (see Figure 1 for examples). Your bone density test result also includes a Z-score that compares your bone density to what is normal in someone your age and body size. Z-score calculator, p-value from z-table, left tail, right tail, two tail, formulas, work with steps, step by step calculation, real world and practice problems to learn how to find standard score for any raw value of X in the normal distribution. Karena berdistribusi normal maka bentuk grafiknya sebagaimana disamping dengan nilai rata-rata dan sudah diketahui n mahasiswa = 1000 serta s baku = 10. This second calculator allows you to calculate the z-score for any given cummulative probability level (simply put, for any given value of p). Percentile doesn't mean a lot, but I don't think it's because the tests are skewed. gives Q, the probability that the observed z score is due to chance. A Z-Score is a statistical value that tells you how many standard deviations a particular value happens to be from the mean of the entire data set. Similarly, not all standard scores come from a normal. (ZUSPOP is a good one if you can’t think of anything). Enter a value, population mean and the standard deviation (for the population). If the Z score is zero, this says that the raw score was equal to the mean of raw scores. The area represents probability and percentile values. Then press ·. In this tip, we will demonstrate how to use T-SQL to perform a Z-score normalization. One should take into account these differences when choosing a formula to calculate Z-scores. The following ranges should be used to understand T-scores for osteoporosis:. Z-score to P-value Calculator. Z-score charts typically only go up to 3. 5 as examples of using StatCrunch to find the - score of a given probability of the standard normal distribution. Compute answers using Wolfram's breakthrough technology & knowledgebase, relied on by millions of students & professionals. 0 z-scores (three standard deviations below the average). One internet resource adviced that I need the package Rbasic (does not exist). Very high or very low (negative) z-scores, associated with very small p-values, are found in the tails of the normal distribution. Once measured, the manufacturers’ software uses the BMD to calculate a T-score and/or Z-score. Altman's Z score is probably one of the more famous credit scoring models have survived 30 years of application more than that. The exception is when weight is included to calculate. Z-Score Calculation Example: The mean of a dataset is 20 and the standard deviation is 7. The area represents probability and percentile values. This calculator will compute a Z-score (i. A Z-score serves to specify the precise location of each observation within a distribution. You could view this as a z-score. 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. Cub Training said It was very nice article and it is very useful to SAS OC learners. 2), you don't need to know how the 1. Practice: Calculating z-scores. Note: If you are given the z-score for a question, skip to Step 2. The exception is when weight is included to calculate. n To find the T score, compute the Z score and then multiply Z by 10 and add 50:. 2 was calculated to find P(Z<1. DEXA bone scan results scores are measured as "T-scores," which is a comparison of a person's bone density with that of a healthy 30-year-old of the same sex. Z = It denotes the Z score value. In another way, it also refers to the number of scores students attained on a test. Formula for T-Score X = Raw score of student Y = Average Score of the whole cohort Z = Standard Deviation. We don't find it because this table doesn't contain negative z-scores. Loading Unsubscribe from Dr. *Note: Application of recommendation may vary according to local requirements. 5 or less at the femoral neck. I have a percentile data set bmiage from the CDC that includes the L,M, and S data---is there a formula in Excel that will calculate the Z-score and the percentile that corresponds to that Z score for a given parameter? I need to be able to determine the child's percentile on a given day based on age and BMI for children age 2 and above. The z-scores are also listed on this normal distribution to show how the actual measurements of height correspond to the z-scores, since the z-scores are simple arithmetic transformations of the actual measurements. Calcu Nation Geometry. 09 z-score is 0. There are two separate charts for z-scores above and z-scores below the mean. Each z-score corresponds to a point in a normal distribution. LARS Score Questionnaire: The aim of this questionnaire was to assess the bowel function using a validated questionnaire. Download this calculator in an excel file or take a Crash course in Z-scores. The calculator allows area look up with out the use of tables or charts. The z-table value for a z-score of 2. For this reason z-scores are often converted to a scale where negative value are not possible. The Boston Children's Hospital Z-Score Calculator allows for the calcuation of the standard score (z-score) of various regressions based on data gathered over the past 12 years on normal children. Early applications of probability involved understanding games of chance, which can be viewed as repetitions of independent events. RAND 36 Score Calculator RAND 36-Item Health Survey v1. However, you may want to remember the mean so write it down if that’s the case. Note that table entries for z is the area under the standard normal curve to the left of z. 5 For 25-yr-olds Z-score and T-score will be the same. 49, so how do I find the probability of a Z-score equaling 4?. The values presented in the graphs above are approximations derived from the work of Abramowitz & Stegun. A negative z-score indicates that the data point is less than the mean, and a positive z-score indicates the data point in question is larger than the mean. 0, when compared to other 80-year-old women, she could very well have a Z score of +1. 5 is not "pre-osteoporosis" or a medical condition, but it is very important for people with low bone density to develop a good plan to prevent bone loss and osteoporosis. As it is very important to use this scoring tool correctly, it is strongly recommended to complete the tutorial before first use. It changes based on operating system, background processes activity and targeted applications. It shows us that the score is equal to the mean, below the mean or above the mean. 95 On the one side, we have 0. Like z-score, t-scores are also a conversion of individual scores into a standard form p-value is the probability that your null hypothesis will be rejected. Feedback appreciated! Available on the Apple App Store. One should take into account these differences when choosing a formula to calculate Z-scores. Presented by Russ Curtis, PhD. If we normalize the data into a simpler form with the help of z score normalization, then it’s very easy to understand by our brains. This site uses cookies to store information on your computer. We looked up the Z Score for -2. In the screencast, the mean values for each scaled score is entered first (i. Z-scores, therefore, are a useful way of standardising values. What if the Z Score is off the Chart? Don’t panic. You need the population standard deviation to calculate a z-score, whereas the t-test makes predictions about the population from the sample statistics, and thus needs no. The basic score on any test is the raw score, which is simply the number of questions a student answered correctly. What I meant by ‘in most situations’ is that the test considers that a given value can be either above or below a given value, so the probability takes that into account and the test is called ‘two-tailed’, as it apparently is in your situation. This second calculator allows you to calculate the z-score for any given cummulative probability level (simply put, for any given value of p). Memory should be splitted in multiple sticks based on architecture of your motherboard. Online Gate Percentile Calculator, How to Calculate Gate Percentile The GATE percentile is calculated as follows: P = ( (N- your rank)/ N) x 100 Where P is percentile and N is total number of candidates appeared for GATE 2012 exam in your stream. wiesen@appliedpersonnelresearch. This wikiHow teaches you how to calculate a Z score in Microsoft Excel. [12] [13] [14] In bone density measurements, the T-score is the standard score of the measurement compared to the population of healthy 30-year-old adults. Given the critical t score from above of 3. We scroll down the left hand column again looking for the corresponding z-score of 2. Now with display of growth needed to maintain percentile. A score that is 30 points below the mean. Your financial well-being is about more than your income or credit score. 13% above the mean for a percentile of 84. This z score calculator calculates the z score based on the given raw score, the mean, and the standard deviation. As you read educational research, you’ll encounter t-test and ANOVA statistics frequently. 6% retrospective, 16. For each column I then add another column that is its respective z score relative to the entire population. Z-Score Calculation Example: The mean of a dataset is 20 and the standard deviation is 7. Solved: Hi guys, I'd like to calculate percentile based on z-score. Often it can be useful to transform your raw scores into Z-scores. Now, let's think about how he did on the MCAT. The z-score formula doesn’t say anything about sample size; The rule of thumb applies that your sample size should be above 30 to use it. pdf to calculate the P value. • In the dialog box, enter 200 for Lower Bound, 220 for Upper Bound, 210 for μ and 10 for σ. Unless otherwise stated, we can assume an alpha level of 0. This raw score calculator will find a raw score given a z-score, mean, and standard deviation. 3 has Z-score of +0. Standard Score. A Z-Score is a statistical value that tells you how many standard deviations a particular value happens to be from the mean of the entire data set. The T-test is similar to the Z-test, but generally T-tests are most helpful with a smaller sample size (typically under 30) and when the standard deviation is unknown, whereas Z. In order to record a 'T' score, the golfer must have played in an organized tournament. The Altman Z-Score was published in 1968 by Edward Altman, and measures a company’s financial heatlth. 60 to the right, cumulative area is. 71 : 2nd -2. 2 and need to calculate P(Z<1. Z Score vs T Score. P Value from T Score Calculator. Note the standard, acceptable and perfect score on the chart. It shows us that the score is equal to the mean, below the mean or above the mean. (You should arrive at the same probability,. Using critical value Z Scores on short term averages 5--20 SMA's is a 50/50 win loss rate, a loser for trends and questionable for range trading days. A Z score can be determined by multiplying the Ppk score by 3. Sample question: A candidate for a job takes a written test where the average score is 1026 and the standard deviation is 209. Like z-score, t-scores are also a conversion of individual scores into a standard form p-value is the probability that your null hypothesis will be rejected. Calculate Z-scores for WorldCom using annual 10-K financial reports for years ending December 31, 1999, 2000 and 2001. The scores range from 200 to 800 for every section, and the total is 2400. Percentile : z Score : Percentile : z Score : 1st -2. • If your T-score is -1 or greater: your bone density is considered normal. If the data can be considered normally distributed and a random sample is taken from a population, then as the sample size becomes large, approximately half the z-scores should be negative and half of the z-scores should. This calculator will compute a Z-score (i. The basic score on any test is the raw score, which is simply the number of questions a student answered correctly. pdf to calculate the P value. A scale score is a conversion of the raw score onto a scale that is common to all test forms for that assessment. In educational assessment, T-score is a standard score Z shifted and scaled to have a mean of 50 and a standard deviation of 10. Where: z is the standard score or Z-score, x is the raw score to be standardized, μ is the mean of the population, σ is the standard deviation of the population. You would need to use the mean and the standard deviation and the z-score of 1. 13% above the mean for a percentile of 84. , 100% correct) is scaled to be reported as 99, and the minimum possible score is scaled to be reported as 0 (zero). For large samples (~>30), they become the same thing. The normal for Z-score. Osteoporos Int 2003 14:13-8. Both T-scores and Z-scores are derived by comparison to a reference population on a standard. We will use T-SQL's AVG() function to calculate the mean and the. It changes based on operating system, background processes activity and targeted applications. A score of zero is associated with very low risk. The mean Z-score, though less commonly used, has the advantage of describing the nutritional status of the entire population directly without resorting to a. To standardize, I've used z-score method that calculates z-score on the total ultimate score , and then took a cue from IQ tests that use mean 100 and std deviation of 15 to arrive at a standardized score for any given individual. The standard score (more commonly referred to as a z-score) is a very useful statistic because it (a) allows us to calculate the probability of a score occurring within our normal distribution and (b) enables us to compare two scores that are from different normal distributions. There are plenty of algorithms around to do that calculation, but I need to do a reverse lookup. Finding the z-Score of the Standard Normal Distribution We selected Q7. You can use our z-score calculator to determine this value for you. 5 at the femoral neck or spine after appropriate evaluation to exclude secondary causes; Low bone mass (T-score between -1. Step 3: find the Z score. This second calculator allows you to calculate the z-score for any given cummulative probability level (simply put, for any given value of p). Enter the three values, then you will get an answer and step-by-step explanation on how you can convert a z-score to a raw score yourself. Supply a vector of scores, and scale() returns a vector of z-scores along with, helpfully, the mean and the standard deviation. You can manually enter the total score, or choose to have GradeBook calculate the total score automatically. Z-score = -0. The score range is from 0 to 5. In Part 1 of the series, we demonstrated how a regression-based normative (RBN) equation can be embedded in a spreadsheet to calculate an estimated IQ score. Standardizing is just like changing units (for example, from Fahrenheit to Celsius). If the z score is positive it is above the mean, than you know that the answer must be higher than 50%. Bone Density T-Score. 5 means that your statistic is 2. If we normalize the data into a simpler form with the help of z score normalization, then it’s very easy to understand by our brains. If you already know the 1. Z score tables sometimes only go up to 3. I hope this helps,. For your English score, the average score for your group was 83. The essential difference between a z-score and t-test is that the z-score provides and requires information about the ___ whereas the t-test makes estimates from the ___. I just got my T score result, but she didn't give me a Z score. Z-benchmark) A benchmark sigma (z-bench) score offers an fair comparison for products or processes. Where: z is the standard score or Z-score, x is the raw score to be standardized, μ is the mean of the population, σ is the standard deviation of the population. In this context, a T Score of 50 is precisely average, with a normal range of roughly 40 to 60. There are the diverse application of z-score across fields if applied properly. 5\)? Using the formula above, we find that \[ T = 50 + 10Z = 50 + 10 \times 2. The bone density test results have two different reports, the T-score and the Z-score. While many tests utilize similar methods to derive their scores, it is also important to note that each test is different and scoring methods may not be the same from one test to another. T-scores have a mean of 50 and standard deviation of 10. This online calculator calculates z score from p value. Between Expected and Actual Academic Achievement Scores: A Step-by-Step Tutorial Jim Wright, Syracuse City Schools (Last upated: 24 Nov 02) Introduction. This gives us a critical Z score of: 1. test(VarA, conf. A z-score less than 0 represents an element less than the mean. The simplest method is to define the scores as an array, in the same order as the letters: int[] letterScore = {1, 3, 3, 2 4, 10}; Then your whole for-cycle gets reduced to. Again, this can be accomplished in one call using scale(). If your t-score is higher than the number listed in the. 5 Z Scores 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. Calculate Z-scores Version: 2019. In this case, the mean would be 2 + 4 (add the two middle numbers), which equals 6. 13% above the mean for a percentile of 84. Standard normal score (Z-score): where x is the raw score to be standardized, μ is the population mean, and σ is the population standard deviation. You could view this as a z-score. A score that is 30 points below the mean. So now we have all ingredients to calculate the z-score which is defined as follows: This means, for every measurement just subtract the mean and divide it by standard deviation. 33 Low Average. 0 z-scores (two standard deviations below the average) and -3. T-scores are another type of standardized score, where 50 is average, and about 40 to 60 is usually considered the average range. 25 Since a T-score is calculated in this example as: T= 50+10z T= 50 + 12. Z score tables sometimes only go up to 3. 0, when compared to other 80-year-old women, she could very well have a Z score of +1. Arrange the scaled scores in order from highest to lowest. As you read educational research, you’ll encounter t-test and ANOVA statistics frequently. The Z score allows you to calculate the probability that a normally distributed random variable x will fall within a desired. org) Comparing with z-scores. I hope this helps,. So what DXA score means I have osteoporosis?. If your t-score is higher than the number listed in the. c) This woman's BMD measurements were below the mean for her age and ethnicity. 5\)? Using the formula above, we find that \[ T = 50 + 10Z = 50 + 10 \times 2. For math, science, nutrition, history. 06 oz and with SD = 0. On some z-tables you will find that the area corresponding to 1. The score range is from 0 to 5. Computing Z-scores using SPSS. If the Z score is zero, this says that the raw score was equal to the mean of raw scores. 00 is equal to. The result is a z -score which may be compared in a 1-tailed or 2-tailed fashion to the unit normal distribution. The Z score allows you to calculate the probability that a normally distributed random variable x will fall within a desired. 96, you are 95% confident that that Variant Recipe is different than the Control Recipe. We don't find it because this table doesn't contain negative z-scores. Practically speaking, Ppk can be determined by dividing the Z score by three. Just enter your p-value, which must be between 0 and 1, and then hit the button below. 2 was calculated to find P(Z<1. Z scores, or standard scores, indicate how many standard deviations an observation is above or below the mean. There’s no relation to IRR here. If you choose to work with t statistics, you may need to transform your raw data into a t statistic. zscore (a, axis=0, ddof=0) [source] ¶ Calculate the z score of each value in the sample, relative to the sample mean and standard deviation. I need to calculate the T-SCORE Values that would represent the Values of 100 T-SCORE Value 90 T-SCORE Value 80 T-SCORE Value 70 T-SCORE Value 60 T-SCORE Value 50 T-SCORE Value 40 T-SCORE Value 30 T-SCORE Value 20 T-SCORE Value 10 T-SCORE Value 0 T-SCORE Value based on the data that I have in Column J. At the two extremes value of z=oo [right extreme] and z=-oo[left extreme] Area of one-half of the area is 0. Finding the z-Score of the Standard Normal Distribution We selected Q7. 5, you would say that the result is 2. In statistics, a Z score is the number of standard deviations a data point appears on a standard distribution curve of the entire dataset. 5 standard deviations. Enter required numbers for the population mean and the standard deviation and hit Calculate. In educational assessment, T-score is a standard score Z shifted and scaled to have a mean of 50 and a standard deviation of 10. Using Excel, find the z-score that corresponds to the. 5 as examples of using StatCrunch to find the - score of a given probability of the standard normal distribution. 5 in our Normal Distribution Tables with Z Scores so you don't have to! First, note that a Z Score of 2. 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. Z-Score to Percentile Calculator Enter a z-critical value and get the area under the normal curve (a percentage). They are extracted from open source Python projects. To calculate the correct score of a football match Comment/Request Would kindly request the results to be processed now [2] 2018/01/07 03:30 Male / 60 years old level. Most experts recommend using Z-scores rather than T-scores for children, teens, women still having periods and younger men. This concept was adapted to the business and finance world by Dr. So, for this example, the median is 3. Use this Student’s T distribution table to find T critical value given confidence level and degrees of freedom. Z-score, sometimes called standard score, is a measurement of how many standard deviations a point is away from the mean of its data set. Generally applied with sample sizes <30. For example, given a sample mean of 20, an estimated population mean of 22, a sample standard deviation of 3 and a total of 4 observations, you would have a t score of 2. Karena berdistribusi normal maka bentuk grafiknya sebagaimana disamping dengan nilai rata-rata dan sudah diketahui n mahasiswa = 1000 serta s baku = 10. Edward Altman who used it predict the likelihood that a company would go bankrupt. Default is 0. You'll find that WorldCom's Z-score suffered a sharp fall. Coronary calcium score may contribute to risk assessment in people at risk for future cardiovascular events. SPSS Excel one sample T Test. The z-score that corresponds to the 90th. We can calculate the girl's exact z-score by using the formula:. The significance of the correlation coefficient is calculated by using a single sided t-test, following Cohen. How to convert a t score from a z score (psychometrics) Converting raw scores to z scores and t. With this z-score calculator, if you are working with a sample of data, you can introduce the Mean of your data and the Standard Deviation, and when you introduce a score to transform, you will get a Z-Score back. Standard Scores have a. Standard Score. Cpk = (USL. • If your T-score is -2. The sign of a z score tells us the position of the score relative to the mean; Positive z scores: raw scores above the mean; Negative z scores: raw scores below the mean; Example Consider a distribution of raw scores with: Mean = 10, s. SAT scores do not range from 0% to 100%. Z-score Calculator. 5 at the femoral neck or spine) and a 10-year probability of a hip fracture ≥ 3% or a 10-year probability of a major osteoporosis-related fracture ≥ 20% based on the US-adapted WHO algorithm. 40 0 z z With. A T-score (with capital "T"), is a type of normalized score, usually used for test scores, that has a population mean of \(\mu = 50\) and a population standard deviation of \(\sigma = 10\). There’s not a lot left, but there is some. The calculator will return Student T Values for one tail (right) and two tailed probabilities. The mean for a curve ofZ scores is also always 0, and the SD is always 1. For T score, 10and=50 Formula for converting z scores to T scores is: Tz So T101. 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. The calculator allows area look up with out the use of tables or charts. My doubt is : The current situation: when a candidate takes a test , he doesn't know it's of 3 categories. A Z score of 3 refers to 3 standard deviations. Finding z- and t-scores for Confidence Intervals 1. Like z-score, t-scores are also a conversion of individual scores into a standard form p-value is the probability that your null hypothesis will be rejected. Altman's Z score is probably one of the more famous credit scoring models have survived 30 years of application more than that. Student Quincy has a z-score of +2. 5?! With!proportion,!we!can. Selecting two-sided provides the area above Z and below -Z. A z-score specifies the precise location of each X value within a distribution. In educational assessment, T-score is a standard score Z shifted and scaled to have a mean of 50 and a standard deviation of 10. X = The value to be standardized. If you can't find BR's scale,this is the scale from AAMC CBT #10, it should serve as a good reference point. Heller on t score z score osteoporosis: Usually the change in a psa value from one to the next is more concerning than the sole value itself. 2) [assuming from context you know that Z is a standard normal random variable. It takes account of the size of j(x) and weights its value accordingly. Quotes are not sourced from all markets and may be delayed up to 20 minutes. Question 4: Find the T score for above problem when z = -1. If we normalize the data into a simpler form with the help of z score normalization, then it’s very easy to understand by our brains. Dexa centers who perform studies on children have software to generate both values. How to convert a t score from a z score (psychometrics) Converting raw scores to z scores and t. What z-score would be assigned to 6? To 14? To. Parents and teachers fill out the score sheets based on observations they make as they interact with the child in his environment. What is a Z-score? A z-score shows you the distance between an observed score and the mean in units of standard deviations. 1 standard deviations, deviations above the mean, above the mean. 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. This means that Z= 0:253 corresponds to the 40th percentile, that is, P(Z< 0:253) = 0:40. 0 lists a probability of 0. However, the calculator below can calculate z score for arbitrary p value. com/watch?v=dtLLh5ura6g Parts: See also: Create z-scores - SPSS. 6% risk of adverse cardiac event. (A z-score and a t-score are examples of test statistics. This stanadrd Z-score helps to decide whether to keep or reject the null hypothesis. McCall in the 1920's and are just one of many scales. So what DXA score means I have osteoporosis?. Comparison Data - Z-score Applications These Java™ applets will calculate Z-scores and percentiles based on age and sex for certain body composition parameters. Also, a Detection Theory calculator is available, as well as an normal curve range visualization tool. The value of 20 has a Z score of 0, which means it is equal to the mean. [12] [13] [14] In bone density measurements, the T-score is the standard score of the measurement compared to the population of healthy 30-year-old adults. DAP:IQ Standard Percentile Score T-score z-s(ore Stanine. The normal for Z-score. Calculate Z-Scores in Stata. Finding the z-Score of the Standard Normal Distribution We selected Q7. H 1: parameter < value. 6 The LARS consists of five questions and can be used to generate an overall score that translates into no LARS (score 0-20), minor LARS (21-29), and major LARS (30. Z-score bisa berupa bilangan positif atau negatif. Internalizing Problems The Internalizing Problems composite scale T score is 56, with a 90 percent confidence-interval range of 51-61 and a percentile rank of 75. Take a look at your scaled scores on the chart to judge your performers. Like z-score, t-scores are also a conversion of individual scores into a standard form p-value is the probability that your null hypothesis will be rejected. 5 Based on the normal curve, a t-score of 60 is exactly 1 standard deviation above the mean, which means it is 34. n To find the T score, compute the Z score and then multiply Z by 10 and add 50:. Most commonly used in a z-test, z-score is similar to T score for a population.