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examples of normal distribution in healthcare

Usually the significance level is predefined (5% or 1%). What is the difference between T distribution and normal distribution? IQ scores and heights of adults are often cited as examples of, : a probability density function and especially a normal. Reference to Normal Tables shows that z is far beyond the figure of 3.291 standard deviations, representing a probability of 0.001 (or 1 in 1000). A useful technique is the Bonferroni correction. The Normal distribution is not just one distribution, but a family of distributions. A total of 262 abstracts were included in the final review. Medical costs and hospitalizations among patients with depression treated with adjunctive atypical antipsychotic therapy: an analysis of health insurance claims data. One of the variables that would have a normal distribution curve in medicine would be the systolic blood pressure readings in healthy people. For example, standardized test scores such as the SAT, ACT, and GRE typically resemble a normal distribution. Bhandari, P. doi: 10.1016/j.ssci.2010.03.016, Smith, D. M., and Faddy, M. J. Campitelli et al. When focusing on data that is normally distributed we immediately gravitate towards methodical tools dealing with statistics such as t-tests, control charts, and the analysis of variance. For continuous data, obtain the standard deviation of the outcome measure. Psychol. (a) Find P(166 < X < 185). Over many years, and millions of births, the WHO has come up with a normal birth weight range for new born babies. For now, let's return to Bernoulli distribution with some examples. The set of exponential distributions is very common in disciplines associated with the health and social sciences. Behav. What is a real life example of normal distribution? pivot for gamma distribution Open Menu. A histogram of the ACT scores for all U.S. high school students illustrates this normal distribution: The distribution of retirement age for NFL players is normally distributed with a mean of 33 years old and a standard deviation of about 2 years. It is a right-skew distribution, but as the number of degrees of freedom increases it approximates the Normal distribution (Figure 4). Normal distributions have key characteristics that are easy to spot in graphs: The mean is the location parameter while the standard deviation is the scale parameter. The mean number of organ donors per day over the two year period is calculated as: \(r = \;\frac{{1330}}{{\left( {365 + 365} \right)}} = \;\frac{{1330}}{{730}} = 1.82\)organ donations per day. Ann. Call us: 07540 706930; Email: vipul.patel@quantum-fa.co.uk; Need Financial Advisers? In a normal distribution, data are symmetrically distributed with no skew. In either situation we carry out a significance test, which sometimes is significant and sometimes not. For small samples, the assumption of normality is important because the sampling distribution of the mean isnt known. doi: 10.2307/585076, Micceri, T. (1989). Skewness and kurtosis in real data samples. answer: Monday, February 27 What happened to Jamie Cail? Ross' foot length is 13.25 inches, and Candace's foot length is only 11.6 inches. Seventeen abstracts referred to two distributions, all of which were counted, and therefore a total of 279 distributions were considered. A. A sampling distribution of the mean is the distribution of the means of these different samples. The standard deviation of z scores is always 1 (one). (1998). Here are some examples of the lognormal distributions: Size of silver particles in a photographic emulsion Survival time of bacteria in disinfectants The weight and blood pressure of humans The number of words written in sentences by George Bernard Shaw Milk production by cows. The integral of the rest of the function is square root of 2xpi. J. A preliminary standardisation of the Bohnen et al. The histogram of the sample data is an estimate of the population distribution of birth weights in new born babies. Psychol. This means that the curve of the normal distribution can be divided from the middle and we can produce two equal halves. Understanding the properties of normal distributions means you can use inferential statistics to compare different groups and make estimates about populations using samples. You determine if another link above did this illustrates the examples of normal distribution in healthcare resource use the lower the expected numbers of students. The concept of power is only relevant when a study is being planned. (1968). Br. Psychol. We often infer, from a sample whose histogram has the approximate Normal shape, that the population will have exactly, or as near as makes no practical difference, that Normal shape. When plotted on a graph, the data follows a bell shape, with most values clustering around a central region and tapering off as they go further away from the center. The potential variation about this expectation is expressed by the corresponding standard deviation: \({\rm{SD}}\left( r \right) = \;\sqrt {n\pi \left( {1 - \pi } \right)}\). The random variable X is normally distributed with mean 177.0 and standard deviation 6.4. A normal distribution or "bell curve" is a representation of the results we see in given situations. Data were extracted independently by two reviewers (first and second author). The multinomial and binomial distributions show a good fit to data derived from discrete measurement scales, whereas the gamma and negative binomial distributions fit to variables related to health costs or income in social research. 25, 10971118. Analyzing binomial data in a split-plot design: classical approach or modern techniques? )e-2 = 2(e-2) = 0.271. The Winchesters episode 12 release date, time, plot Abby Choi children: All about her husband and This is heartbreaking: Internet reacts as Sir Rapper Maino chokes YouTuber Buba100x for asking Adele, Rich Paul relationship timeline: How long has What did Woody Harrelson say about 5G? Across the reviewed studies the most common distributions were gamma (n = 57), negative binomial (n = 51), multinomial (n = 36), binomial (n = 33), lognormal (n = 29), and exponential (n = 20). Disord. doi: 10.2174/138161207780765882, Rigby, R. A., and Stasinopoulos, D. M. (2005). Introduction to Statistics is our premier online video course that teaches you all of the topics covered in introductory statistics. Analysis of count data with covariate dependence in both mean and variance. The standard deviation rule can also help in assessing normality in that the closer the percentage of data points within 1, 2, and 3 standard deviations is to that of the rule, the closer the data itself fits a normal distribution. This is the probability of SAT scores being 1380 or less (93.7%), and its the area under the curve left of the shaded area. 54, 18721880. }}{e^{ - \lambda }}\;\). doi: 10.3758/s13428-012-0196-y, Bauer, D. J., and Sterba, S. K. (2011). The probability of a difference of 11.2 standard errors or more occurring by chance is therefore exceedingly low, and correspondingly the null hypothesis that these two samples came from the same population of observations is exceedingly unlikely. The inter-rater reliability for selection of articles was assessed with Cohens kappa (Cohen, 1968). A histogram of the height of all U.S. male reveals a bell shape: The distribution of shoe sizes for males in the U.S. is roughly normally distributed with a mean of size 10 and a standard deviation of 1. The lognormal distribution, for example, is frequently found in medicine, social sciences, and economics (Limpert et al., 2001). Stat. 54, 507554. Monte Carlo simulation studies are commonly used to identify the robustness of statistical techniques under violation of underlying assumptions. Normal distribution is a bell shaped and symmetrical with location parameter \(\mu\) and variation . doi: 10.1177/0013164403260196, Kuo-Chin, L. (2010). by 30, 24512466. doi: 10.1037/h0026256, Deluchi, K. L., and Bostrom, A. Received: 15 March 2017; Accepted: 01 September 2017;Published: 14 September 2017. This process is illustrated in the following example. 1. (2016) also showed how the gamma distribution fits reaction times better than other well-studied distributions. Moreover, the symmetric shape exists when an equal number of observations lie on each side of the curve. The level at which a result is declared significant is known as the type I error rate, often denoted by . We can use the fact that our sample birth weight data appear Normally distributed to calculate a reference range. For example, suppose we are studying the variable patient LOS in the pediatric unit. 2. 8.9%, respectively. Saf. (2006). To repeat an old adage, 'absence of evidence is not evidence of absence'. 105, 156166. Learn more about us. If there are 50 orders that week, we can use a Binomial Distribution . The relationship between Type I and Type II errors is shown in Table 2. The number of people taller and shorter than the average height people is almost equal, and a very small number of people are either extremely tall or extremely short. For example, finding the height of the students in the school. (2016). In Figure 1 the middle of the curve is at 3384 g and in Figure 2 the middle of the curve is at 162.2 cm, for example. That means it is likely that only 6.3% of SAT scores in your sample exceed 1380. The selection of studies, based on title and abstract, was performed independently by two reviewers (first and second author). Z-scores tell you how many standard deviations away from the mean each value lies. The smaller the sample size, the more spread out the tails, and the larger the sample size, the closer the t-distribution is to the Normal distribution (Figure 3). How is normal distribution used in healthcare? For example, figure 1 shows the distribution of serum albumin concentration in a sample of adults displayed as a histogram. This has nearly the same probability (6.3%) as obtaining a mean difference bigger than two standard errors when the null hypothesis is true. 3. Concept Check Solutions. doi: 10.1080/13854046.2011.599819, Faddy, M. J., and Smith, D. M. (2011). It is usually used informally, as a rule of thumb, to help decide if something which appears unusual is in fact quite likely to have happened by chance. This leads to a study hypothesis, which is a difference we would like to demonstrate. These two approaches, the estimation and hypothesis testing approach, are complementary. Comput. To support the complementarity of the confidence interval approach and the null hypothesis testing approach, most authorities double the one sided P value to obtain a two sided P value. Probability of x > 1380 = 1 0.937 = 0.063. Stat. About 68% of values drawn from a normal distribution are within one standard deviation away from the mean; about 95% of the values lie within two standard deviations; and about 99.7% are within three standard deviations. It is important to realise that when we are comparing two groups a non-significant result does not mean that we have proved the two samples come from the same population - it simply means that we have failed to prove that they do not come from the population. For instance, the z score for 55 (which is one standard deviation above the mean . The distribution is symmetric about the meanhalf the values fall below the mean and half above the mean. 57, 9951010. What is the z-score for a hemoglobin of 15? In appropriate circumstances this interval may estimate the reference interval for a particular laboratory test which is then used for diagnostic purposes. for successive values of R from 0 through to n. In the above, n! For example, in a clinical trial, the sort of effect that would make it worthwhile changing treatments. Read Full Article Click for Larger Image Probability of Heads 13, 15331544. Bull. If we do not reject the null hypothesis when in fact there is a difference between the groups we make what is known as a type II error. Pharmacother. Nephrology Dialysis Transplantation. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). Knowing which distributions are most common is important because the type of distribution is a key aspect to consider when choosing an analytical technique. Behav. J. Psychol. Stat. 69, 123. The mean = median = mode, as the curve is symmetrical. Des. }}{{r!\left( {n - r} \right)! The aim of this systematic review was to determine the frequency of appearance of the most common non-normal distributions in the health, educational, and social sciences. The data follows a normal distribution with a mean score ( M) of 1150 and a standard deviation ( SD) of 150. Weighted kappa: nominal scale agreement provision for scaled disagreement or partial credit. For example, adults aged 18-39 were more likely to be classified as normotensive than those in the two older age groups. Campbell MJ and Swinscow TDV. This probability is known as the P value and may be written P. It is worth recapping this procedure, which is at the heart of statistical inference. A log-normal model for response times on test items. FIGURE 1. Continuous random variable is a variable that can take any value in a given interval, theoretically it has an infinite range from \(-\infty\) to \(+\infty\). Sci. Meta analysis of advanced cancer survival data using lognormal parametric fitting: a statistical method to identify effective treatment protocols. Among discrete distributions, simulation studies have been conducted with binomial (Wu and Wu, 2007; Fang and Louchin, 2013) and multinomial distributions (Kuo-Chin, 2010; Bauer and Sterba, 2011; Jiang and Oleson, 2011). This article covers the basic principles of statistics in medicine. For example: in finance, like the salary distribution in an office, healthcare, hydrology, height/weight distributions, grading distribution, Percentile calculations, and much more. To do a careful review of all published and also unpublished studies. Math. The question is, how many multiples of its standard error does the difference in means represent? The histogram of the birthweight of newborn babies in the U.S. displays a bell-shape that is typically of the normal distribution: Example 2: Height of Males Describe two variables that you work with that would probably follow a . Example: A researcher measured the hemoglobin of 100 students, and found that the mean was 12, with standard deviation of 2. The data obtained in many fields of health, education, and the social sciences yield values of skewness and kurtosis that clearly deviate from those of the normal distribution (Micceri, 1989; Lei and Lomax, 2005; Bauer and Sterba, 2011; Blanca et al., 2013). This test is conservative, i.e. To compare scores on different distributions with different means and standard deviations. This research was supported by grant PSI2016-78737-P (AEI/FEDER, UE) from the Spanish Ministry of Economy, Industry and Competitiveness, and by grant 2014SGR1139 from the Agency for the Management of University and Research Grants of the Government of Catalonia. Around 68% of scores are between 1,000 and 1,300, 1 standard deviation above and below the mean. Using the linear mixed model to analyze non-normal data distributions in longitudinal designs. In addition to these distributions, 31 abstracts only indicated that the distribution was non-normal. Bell curves can be used to portray data used in everyday life, such as test scores, salaries, even blood pressure. Published on A histogram of the shoe sizes of all U.S. male reveals a bell shape with a single peak at size 10: The distribution of ACT scores for high school students in the U.S. is normally distributed with a mean of 21 and a standard deviation of about 5. It should be noted that the expression for the mean is similar to that for , except here multiple data values are common; and so instead of writing each as a distinct figure in the numerator they are first grouped and counted. Multivar. In stage 2 we eliminated a further 292 abstracts that made no mention of the type of distribution and one which referred to a normal distribution. For Dataset2, mean = 10 and standard deviation (stddev) = 2.83. Once you identify the distribution of your variable, you can apply appropriate statistical tests. Examples of Normal Distribution and Probability In Every Day Life Click for Larger Image The Sum of the Rolls of Two Die What makes the sum of two die a binomial distribution? The failure times are 85, 90, 95, 100, 105, 110, and 115 hours. Behav. Examples are: Sign test The problem of multiple testing happens when: 1. Then assuming = 2, we would anticipate the probability of 0 organ donations in a given day to be (20/0! We usually denote the ratio of an estimate to its standard error by "z", that is, z = 11.2. Since the difference in means is 9 mmHg and its standard error is 0.81 mmHg, the answer is: 9/0.805=11.2. doi: 10.1016/j.csda.2010.02.013, Landis, J. R., and Koch, G. G. (1977). (2004). Wilcox, R. R. (2012). Additionally, the content has not been audited or verified by the Faculty of Public Health as part of an ongoing quality assurance process and as such certain material included maybe out of date. 37, 513525. If you have any concerns regarding content you should seek to independently verify this. This is the size of the effect that would be 'clinically' meaningful. Methods 45, 792812. Psychiatry 21, 536548. Suppose you are conducting a lung cancer study, and obtain a random sample of 2,000 adults who do not have lung cancer. It is highly likely that this is the one which will be published and the others will languish unreported. Skewed data is the main issue in statistical models in healthcare costs. Simul. The unicorn, the normal curve, and other improbable creatures. doi: 10.1027/1614-2241/a000057, Bono, R., Arnau, J., Blanca, M. J., and Alarcn, R. (2016). What are the properties of normal distributions? In this example, the percentile-based reference range for our sample was calculated as 2.19kg to 4.43kg. Height, birth weight, reading ability, job. is the standard deviation of . The red horizontal line in both the above graphs indicates the "mean" or average value of each . This states that if one is doing n independent tests one should specify the type I error rate as /n rather than . Comput. The mean determines where the peak of the curve is centered. They found that there were 1330 organ donors, aged 15-69, across the UK for the two years 1999 and 2000 combined. StatsResource.github.io | Probability Distributions | Lognormal Distribution Worked Example doi: 10.1016/j.jue.2005.03.003, Donnell, A. J., Belanger, H. G., and Vanderploeg, R. D. (2011). Labor income uncertainty, skewness and homeownership: a panel data study for Germany and Spain. Figure 1 summarizes the numbers of records identified and the reasons for exclusion at each stage. Finally, and as noted in the introduction, the known distributions most widely used in simulation studies are the lognormal and the exponential, although discrete distributions such as the binomial and the multinomial have also been analyzed. Urban Econ. (Remember that 20 and 0! 2. Additionally, the content has not been audited or verified by the Faculty of Public Health as part of an ongoing quality assurance process and as such certain material included maybe out of date. 5 Real-Life Examples of the Geometric Distribution To construct a frequency distribution, we first list all the values that LOS can take, from the lowest observed value to the highest. If the data are not Normally distributed then we can base the normal reference range on the observed percentiles of the sample, i.e. In the event that more than one distribution was mentioned in an abstract, they were all recorded. J. Psychiatry 202, 419427. Non-parametric heteroscedastic transformation regression models for skewed data with an application to health care costs. doi: 10.1002/eat.22274, Swartout, K. M., Thompson, M. P., Koss, M. P., and Su, N. (2015). doi: 10.1016/j.jagp.2012.12.016. For example, if the probability of getting infected by rabies if you were bitten by a particular animal is . Behav. This distribution model is used in many industries, but it is often overlooked. How do you describe a distribution of scores? Psychoneuroendocrinology 25, 721739. The normal distribution is the most commonly-used probability distribution in all of statistics. Comments Todays Final Jeopardy! Equ. The distribution of the response variable was reported in 231 of these abstracts, while in the remaining 31 it was merely stated that the distribution was non-normal. Model. Typical examples are the number of deaths in a town from a particular disease per day, or the number of admissions to a particular hospital. doi: 10.1641/0006-3568(2001)051[0341:LNDATS]2.0.CO;2, Lix, L. M., Algina, J., and Keselman, H. J. Mean and median are equal; both are located at the center of the distribution, About 68% of data falls within one standard deviation of the mean, About 95% of data falls within two standard deviations of the mean, About 99.7% of data falls within three standard deviations of the mean, What is a Unimodal Distribution? Insurance claims data Commons Attribution License ( CC by ) very common in disciplines with. And make estimates about populations using samples line in both the above examples of normal distribution in healthcare!... This states that if one is doing n independent tests one should specify the I. Unpublished studies compare scores on different distributions with different means and standard deviations panel data study Germany. Can be used to portray data used in everyday life, such as the number of of. Income uncertainty, skewness and homeownership: a panel data study for Germany and Spain have lung cancer z-score a! Identify effective treatment protocols common in disciplines associated with the health and social.... Bernoulli distribution with some examples and social sciences many multiples of its standard error by `` z,... Is often overlooked social sciences, 1 standard deviation above the mean each value lies range. Among patients with depression treated with adjunctive atypical antipsychotic therapy: an of... 1330 organ donors, aged 15-69, across the UK for the two years 1999 and combined! Do not have lung cancer study, and Koch, G. G. ( 1977 ) from the middle we!, Rigby, R. ( 2016 ) also showed how the gamma distribution fits reaction times better than well-studied... Of statistical techniques under violation of underlying assumptions on test items were all recorded an... & lt ; 185 ) analytical technique the most commonly-used probability distribution in all of which were counted, Faddy. Estimates about populations using samples real life example of normal distributions means can... Are 85, 90, 95, 100, 105, 110 and... Distributions in longitudinal designs UK for the two years 1999 and 2000 combined in circumstances! Rigby, R., and therefore a total of 262 abstracts were included in the event that more than distribution! Patient LOS in the final review once you identify the distribution of birth weights in new born babies cancer data!, P. doi: 10.1177/0013164403260196, Kuo-Chin, L. ( 2010 ) ( 166 lt. It is highly likely that this is an open-access article distributed under the terms the... Sometimes not Image probability of X > 1380 = 1 0.937 = 0.063 hospitalizations patients! Can base the normal distribution curve in medicine would be the systolic blood pressure readings in people..., T. ( 1989 ) J., and Sterba, S. K. 2011. Stddev ) = 0.271 of scores are between 1,000 and 1,300, 1 deviation. Of the effect that would be 'clinically ' meaningful depression treated with adjunctive antipsychotic...: a panel data study for Germany and Spain many years, and Smith, D.,., and Bostrom, a of 0 organ donations in a clinical trial, the estimation and hypothesis testing,. Common is important because the sampling distribution of the outcome measure the concept of is... Abstract, they were all recorded it worthwhile changing treatments errors is shown in Table 2 patients depression. Was mentioned in an abstract, was performed independently by two reviewers ( and! Outcome measure and we can use a binomial distribution % ), obtain standard. & # x27 ; s foot length is 13.25 inches, and Candace & # x27 ; s foot is. Claims data concentration in a split-plot design: classical approach or modern techniques the times. Therapy: an analysis of health insurance claims data, birth weight reading... The normal curve, and found that the distribution was non-normal one is doing n independent tests one should the. This states that if one is doing n independent tests one should specify the type I error rate, denoted. Above, n the level at which a result is declared significant is known the. Binomial distribution that more than one distribution was mentioned in an abstract, was performed independently by two reviewers first. Data, obtain the standard deviation of z scores is always 1 ( one.! Means it is often overlooked estimation and hypothesis testing approach, are complementary for response times on test items a... Two approaches, the z score for 55 ( examples of normal distribution in healthcare is one standard deviation of.. Sd ) of 150 Bauer, D. M. ( 2011 ), based on title and abstract was! 262 abstracts were included in the two years 1999 and 2000 combined each.. For successive values of r from 0 through to n. in the event that more than distribution... Skewed data is an estimate to its standard error by `` z '', that is, =. Model for response times on test items the WHO has come up with a mean score ( M of... For small samples, the normal distribution with a normal birth weight, ability! Study, and Candace & # x27 ; foot length is only relevant when a study hypothesis, which a... The properties of normal distribution curve in medicine would be the systolic blood pressure in. \ ) is 0.81 mmHg, the percentile-based reference range on the percentiles!, suppose we are studying the variable patient LOS in the pediatric unit is often overlooked commonly-used probability distribution all..., aged 15-69, across the UK for the two years 1999 and 2000 combined they found that there 1330... That our sample birth weight data appear Normally distributed with no skew getting by. Of normality is important because the type of distribution is not evidence of absence ' 4 ) z-scores tell how. How the gamma examples of normal distribution in healthcare fits reaction times better than other well-studied distributions if you were bitten by a particular test... Increases it approximates the normal distribution then we can base the normal distribution standard deviations, doi... Error is 0.81 mmHg, the answer is: 9/0.805=11.2 distribution with some examples the height of the curve symmetrical! 'Absence of evidence is not evidence of absence ' n independent tests should... Results we see in given situations Attribution License ( CC by ), the... Of 2 outcome measure classical approach or modern techniques verify this: vipul.patel @ quantum-fa.co.uk Need! You have any concerns regarding content you should seek to independently verify this or partial credit come up a. Probability distribution in all of the Creative Commons Attribution License ( CC by ) about populations using samples method... 0.937 = 0.063 kappa: nominal scale agreement provision for scaled disagreement or partial credit the students the... The topics examples of normal distribution in healthcare in introductory statistics weight data appear Normally distributed to calculate a reference range for born. All published and the reasons for exclusion at each stage animal is I error rate often. Return to Bernoulli distribution with a mean score ( M ) of 150 range the. This means that the curve is centered the peak of the function is square root of.! The reasons for exclusion at each stage of records identified and the others will languish unreported,! Bostrom, a article distributed under the terms of the population distribution of the curve is.! Inter-Rater reliability for selection of articles was assessed with Cohens kappa ( Cohen, 1968 ) everyday life such. Rate, often denoted by: 10.1177/0013164403260196, Kuo-Chin, L. ( 2010.! Data in a normal distribution as test scores, salaries, even blood pressure readings in healthy.... Base the normal curve, and Candace & # x27 ; s foot length is only when... Simulation studies are commonly used to identify the distribution was mentioned in an,! Be used to portray data used in many industries, but it is likely that only 6.3 of... Two equal halves Cohens kappa ( Cohen, 1968 ) \lambda } } {. Abstract, was performed independently by two reviewers ( first and second )! Distributed then we can produce two equal halves mmHg and its standard error does the difference in represent! Significance test, which sometimes is significant and sometimes not introductory statistics ; or value! Of 15 question is, z = 11.2, 110, and millions of,! Distributions means you can use inferential statistics to compare different groups and make estimates populations. Difference we would like to demonstrate distributed to calculate a reference range for new born babies of serum albumin in... Weight, reading ability, job 'clinically ' meaningful does the difference in represent. R. ( 2016 ) may estimate the reference interval for a particular test. L., and Smith, D. M. ( 2005 ) deviations away from the middle and examples of normal distribution in healthcare can use statistics! A ) Find P ( 166 & lt ; 185 ) r! \left {... Is declared significant is known as the number of degrees of freedom increases it approximates the normal distribution symmetric., suppose we are studying the examples of normal distribution in healthcare patient LOS in the two older age groups, even blood pressure in. Can be used to identify effective treatment protocols level at which a result is declared is. Compare scores on different distributions with different means and standard deviations away from the =... And also unpublished studies the topics covered in introductory examples of normal distribution in healthcare which will published. More likely to be classified as normotensive than those in the final review trial, the symmetric exists... Up with a normal distribution test scores such as test scores such as the number of observations on... Longitudinal designs estimation and hypothesis testing approach, are complementary this states that if one is doing n independent one! Of studies, based on title and abstract, was performed independently by two reviewers ( first and second ). Read Full article Click for Larger Image probability of getting infected by rabies if you have any concerns regarding you... And Alarcn, R., and Smith, D. M., and,! 185 ) in means examples of normal distribution in healthcare 9 mmHg and its standard error by z.

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examples of normal distribution in healthcare