 • November 2nd, 2018

# Statistics

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Overview I have provided you with an excel file (Exam1_data.xlsx) that contains 5 pyrethroid pesticide metabolites measured in dust samples collected in 85 homes and day-care facilities. The file contains two spreadsheets. The first sheet (Metabolite_data) contains the sample data, having concentrations of the metabolites reported in ng/g. Concentrations below the method detection limit are indicated by ‘nd’. The second sheet (MDL_data) contains the method detection limits for each of the metabolites, also reported in units of ng/g. These data are from a research publication that has also been provided to you for added perspective. It is not a requirement to read the paper in detail to perform the tasks associated with this Exam. Exam Instructions 1) Read these instructions completely and review the data set. Based on what you have learned thus far perform the following steps. 2) Detection Frequency and Data Substitution a. Calculate the frequency of detection for each of the analytes. Present the results in tabular form. [5 pts] b. Make a decision regarding the substitution of values that were below the detection limit. This could be one of the analytes or all of them, but your decision will not be none of them. Describe your reasoning for selecting which analytes to substitute the below detection data. [10 pts] c. Substitute the ‘nd’ values using a method of your choosing. Describe your reasoning for selecting the method to substitute the below detection data. [10 pts] d. Calculate the concentration distributions for each metabolite as is, and for where an analyte has substituted values). Present results in a tabular form, using the following percentiles of the distribution (0, 1, 5, 10, 25, 50, 75, 90, 95, 99, 100) and also presenting the arithmetic mean and standard deviation. Describe any differences in the distribution statistics (if any). [30 pts] e. Visually compare and present the two distributions (with and without data substituted) for analytes where you have substituted for the below-detection data using an E-CDF. Describe any differences in the distribution (if any). [15 pts] 3) Evaluation for Outliers a. Approximate the distribution forms using QQ plots to determine normality. [10 pts] b. Based on the distribution form, select an appropriate approach (either a parametric or non-parametric test) to conduct an outlier analysis. Discuss approach selected and the reasoning for its selection. [10 pts] c. Where potential outliers have been identified (if any), calculate new distribution statistics (i.e., means, standard deviations, percentiles) for the new metabolite distribution. Discuss differences to the distributions (with all data and following outlier removal, if any) by comparing their descriptive statistics [10 pts] 4) Provide tables and figures in excel sheets

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