Summary statistics present a statistical and visual overview of independent samples. A side-by-side combined dot-, box-, mean-, percentile- and SD-plot give a visual summary and statistics such as the mean, median, standard deviation, percentiles, quartiles, skewness and kurtosis summarise the sample numerically.
The requirements of the test are:
Data in existing Excel worksheets can be used and should be arranged in a List dataset layout or Table dataset layout. The dataset must contain a continuous scale variable and a nominal/ordinal scale variable containing two or more independent groups.
When entering new data we recommend using New Dataset to create a new 2 variables (1 categorical) dataset ready for data entry.
To start the summary statistics test:
Excel 97, 2000, 2002 & 2003:
Select any cell in the range containing the dataset to analyse, then click Analyse on the Analyse-it toolbar, click Compare Groups then click Summary.
The report shows box and mean plots and summary statistics for the sample. Summary statistics include the number of observations analysed, the mean, median, standard deviation, standard error, min, max and interquartile range (IQR).
Confidence intervals are calculated for the mean and median. The interval shows, for the chosen level of certainty, the range of the true underlying population mean or median.
To change the confidence interval calculated:
Dot plots show individual observations to allow visual assessment of the distribution and clustering of observations, and to spot possible outliers or data entry errors. Observations are plotted on the X axis against a random value on the Y axis to minimise overlapping points.
To show dot plots on the univariate plot:
Box and percentile plots show the non-parametric central tendency, dispersion and distribution shape of the sample. Box plot styles vary between publications, with the most common styles mainly differing in how the whiskers are drawn. The box plot style determines how the whiskers are shown:
The box-plot can be shown as a rectangular box, or notched to show the confidence interval of the median.
To change the box plot:
To hide box plots:
The range between two percentiles can be shown on the box or dot plots (the percentile values are also shown in the percentile table). The range can show where 80%, 90%, 95% or 99% of the observations of the sample lie.
To change the percentiles shown:
Mean and SD plots show the parametric central tendency, dispersion and distribution shape.
The mean plot shows the mean as a vertical line, and optionally, the confidence interval for the mean as a diamond shape.
To change the mean plot:
SD plots are similar to non-parametric percentile plots, but show the parametric dispersion of the sample. They are useful for assessing the symmetry and skew of the distribution, and can show the dispersion of mean ± 1, 2 or 3 standard deviations or a range from the normal distribution.
To change the SD plot:
To hide the mean and/or SD plot: