2 The National Institute Of Standards And Technology Nist Offers A Wide Variety Of Standard Reference Materials Srm 1 (81.03 KiB) Viewed 94 times
2. The National Institute of Standards and Technology (NIST) offers a wide variety of standard reference materials" (SRMs) with accurately specified analyte concentrations SRM 3667 is intended "primarily for use in evaluating the accuracy of procedures for the determination of creatinine in human urine." The certified value for creatinine in SRM 3667 is 61.80 mg/dL (concentration units commonly used in dinical chemistry), which we will take as the "true" value, . We will use this standard to test a method with an intrinsic variability (for an experienced analyst) of o = 2.8s mg/dL. a. (1 pt) Table 4-1 lists Gaussian probabilities for incremental values of . Conversely, the bottom row of Table 4-4 lists exact values of that correspond to specified probabilities ("levels of confidence"). For what value of -does exactly 95% of the area under a Gaussian curve lie between Use this multiplier to find the range of measured creatinine concentrations that would indude 95% of the trials from the "parent population" (and a given above. b. (1 pt) Calculate for a trial in which the measured creatinine concentration is 64.7 mg/dL. c. (1 pt) Table 4-1 only indudes : values to the nearest 0.1. Fortunately, accurate areas for any value of z can be determined numerically. The TwoGaussians.xlsx spreadsheet posted to Canvas calculates the area from 0 to the value of : entered in cell H2. Using from part b, calculate the probability that a trial will fall within of the true mean. What is the complementary) probability that a trial will fall outside this range? Sketch Gaussian curves with these areas shaded. d. (1 pt) What is the probability that a trial will give a creatinine concentration below 64.7, mg/dL? What is the complementary) probability that a trial will give a creatinine concentration above 64.7, mg/dL? Again, sketch these areas. 3. You performed the analysis described in question 2. In three trials, you obtained the following creatinine concentrations (all in mg/dL): 69.53, 64.84, 66.72. a. (1 pt) Writing out all work, calculate the experimental mean and standard deviation. Keep two guard digits throughout (unless all trailing digits are exactly zero) to prevent rounding errors from accumulating. [See the Significant Figures handout.] b. (1 pt) Again showing all work, calculate a 90% confidence interval for your measured creatinine concentration and write it as an intermediate result (with guard digits). Does your measurement differ from wat 90% confidence? c. (1 pt) Repeat part b for 95% confidence and explain any change in your conclusion. d. (1 pt) Another student performed the same analysis and in n = 5 trials measured * = 63.43 mg/dL and s = 1.87 mg/dL (not "significantly different from your standard deviation). Does the other student's measurement differ from yours at 95% confidence? Show all work, including the value of fun you used.
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Use this multiplier to find the range of measured creatinine concentrations that would indude 95% of the trials from the "parent population" (and a given above. b. (1 pt) Calculate for a trial in which the measured creatinine concentration is 64.7 mg/dL. c. (1 pt) Table 4-1 only indudes : values to the nearest 0.1. Fortunately, accurate areas for any value of z can be determined numerically. The TwoGaussians.xlsx spreadsheet posted to Canvas calculates the area from 0 to the value of : entered in cell H2. Using from part b, calculate the probability that a trial will fall within of the true mean. What is the complementary) probability that a trial will fall outside this range? Sketch Gaussian curves with these areas shaded. d. (1 pt) What is the probability that a trial will give a creatinine concentration below 64.7, mg/dL? What is the complementary) probability that a trial will give a creatinine concentration above 64.7, mg/dL? Again, sketch these areas. 3. You performed the analysis described in question 2. In three trials, you obtained the following creatinine concentrations (all in mg/dL): 69.53, 64.84, 66.72. a. (1 pt) Writing out all work, calculate the experimental mean and standard deviation. Keep two guard digits throughout (unless all trailing digits are exactly zero) to prevent rounding errors from accumulating. [See the Significant Figures handout.] b. (1 pt) Again showing all work, calculate a 90% confidence interval for your measured creatinine concentration and write it as an intermediate result (with guard digits). Does your measurement differ from wat 90% confidence? c. (1 pt) Repeat part b for 95% confidence and explain any change in your conclusion. d. (1 pt) Another student performed the same analysis and in n = 5 trials measured * = 63.43 mg/dL and s = 1.87 mg/dL (not "significantly different from your standard deviation). Does the other student's measurement differ from yours at 95% confidence? Show all work, including the value of fun you used.