tailieunhanh - Exploratory Data Analysis_4

Tham khảo tài liệu 'exploratory data analysis_4', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | . Histogram Interpretation Bimodal Mixture of 2 Normals Recommended Next Steps If the histogram indicates that the data might be appropriately fit with a mixture of two normal distributions the recommended next step is Fit the normal mixture model using either least squares or maximum likelihood. The general normal mixing model is M pộl 1 -p 02 where p is the mixing proportion between 0 and 1 and 01 and 02 are normal probability density functions with location and scale parameters A4 ơl 2 and 2 respectively. That is there are 5 parameters to estimate in the fit. Whether maximum likelihood or least squares is used the quality of the fit is sensitive to good starting values. For the mixture of two normals the histogram can be used to provide initial estimates for the location and scale parameters of the two normal distributions. Dataplot can generate a least squares fit of the mixture of two normals with the following sequence of commands RELATIVE HISTOGRAM Y LET Y2 YPLOT LET X2 XPLOT RETAIN Y2 X2 SUBSET TAGPLOT 1 LET U1 estimated value from histogram LET SD1 estimated value from histogram LET U2 estimated value from histogram LET SD2 estimated value from histogram LET P FIT Y2 NORMXPDF X2 U1 S1 U2 S2 P NIST SEMATECH HOME TOOLS AIDS SEARCH BACK NEXT http div898 handbook eda section3 2 of 2 5 1 2006 9 56 39 AM . Histogram Interpretation Skewed Non-Normal Right hW ENGINEERING STATISTICS HANDBOOK TOOLS raids ISEAtCH back NEKT 1. Exploratory Data Analysis . EDA Techniques . Graphical Techniques Alphabetic . Histogram . Histogram Interpretation Skewed Non-Normal Right Right-Skewed Histogram Discussion of Skewness A symmetric distribution is one in which the 2 halves of the histogram appear as mirror-images of one another. A skewed non-symmetric distribution is a distribution in which there is no such mirror-imaging. For skewed distributions it is quite common to have one tail of the .