Data Transformation, T-Tools and Alternatives

1. Describing and Displaying Data

2. Data Transformations

3. Tests for Differences betweenTwo Independent Samples / Two

Paired Samples

3 principal procedures for describing and exploring continuous data:

Analyze Descriptive statistics FrequenciesDescriptivesExplore

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.

Single group

More than one groups (use labels)

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

Compute Variables e.g. Natural Logarithm Transform

The type depends on the form of the distribution of the variable on the original scale.

Some recommended data transformations :

used for paired (matched) data

Paired-Samples T Test

Read output

Independent-Samples T-Test

Assume Equal variances or not?! ---- refer to Levene’s test result

Tips for the assignment

Generally~

Read the question carefully.

Follow the marking schema

Q4 & Q8 bNull 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