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Data Transformation, T-Tools and Alternatives
Lab 1 Instruction Data Transformation, T-Tools and Alternatives
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Topics 1. Describing and Displaying Data 2. Data Transformations
3. Tests for Differences between Two Independent Samples / Two Paired Samples
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1.Displaying and Describing Data
3 principal procedures for describing and exploring continuous data: Analyze Descriptive statistics Frequencies Descriptives Explore
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Frequencies procedure
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Descriptives procedure
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Explore Procedure The Explore procedure in SPSS allows you to obtain descriptive statistics for your data, identify extreme observations, calculate the percentiles of the distribution, and display the data with a variety of plots.
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Explore Procedure
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Explore Procedure
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Explore Procedure
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Boxplots Single group
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Boxplot More than one groups (use labels)
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Boxplot
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Normality Plots – Q-Q Plots
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Describe the data Center: mean; median Spread: s.d.; IQR=Q3-Q1
Shape: symmetric VS skewed (left/right) Outliers: <Q1-1.5*IQR or >Q3+1.5*IQR Normality according to boxplot/QQ plot/Kolmogorov-Smirnov test
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2. Data Transformations Compute Variables e.g. Natural Logarithm Transform
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Natural Logarithm Transformation
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Other Useful Data Transformations
The type depends on the form of the distribution of the variable on the original scale. Some recommended data transformations :
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3. Tests for Differences between Two Paired Samples
used for paired (matched) data Paired-Samples T Test
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Read output
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4. Tests for Differences between Two Independent Samples
Independent-Samples T-Test
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Assume Equal variances or not?! ---- refer to Levene’s test result
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Tips for the assignment Generally~ Read the question carefully
Tips for the assignment Generally~ Read the question carefully. Follow the marking schema
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Q4 & Q8 b Null hypothesis, Alternative hypothesis; value of the Test statistic; p-value; Conclusion; (maybe) Confidence interval. Q8 a&c “the differences in LLSIR on the log scale between normal and hypoplastic lungs” VS “the ratio of mean LLSIR of normal lungs to that of hypoplastic lungs” use antilogrithm, see Page 16 in the instruction
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