Analysis | Visual | Segment | Impact on Target
This new feature allows comparing a segment with a selected benchmark (either the entire data set, or another segment). The comparison is done in terms of Impacts, a term combining the difference of the observable variables' mean values and their effect on the Target node.
The Impactfor each observable variable is computed as follow:
is the analyzed segment,
is the benchmark,
is the mean value of on the data set defined by the segment or the benchmark,
is the effect of on the Target node, evaluated on the benchmark.
Four types of effects are available:
Null Value Assessment
This option allows estimating if the segment and benchmark mean values are significantly different. Two tests are proposed for answering this question:
- a Frequentist one, NHST t-test, the Null Hypothesis Significance Testing with the Welch's two-sample, two tailed t-test, and
- a Bayesian one, BEST, described in the paper by John K. Kruschke, "Bayesian Estimation Supersedes the t-test", Journal of Experimental Psychology: General, 2013.
Below is the Bayesian network used in the BEST approach. We are assuming that the samples follow a Student's t-distribution. The segment and the benchmark have their ownand , but they share the same .
The default Confidence Level has been set to 95%. This is the same for both tests.
As for the Bayesian test, the Region of Practical Equivalence (ROPE) on the Effect size around the null value has been set by default to [-0.1, 0.1].
The null value is declared to be rejected if the 95% Highest Density Interval (HDI) falls completely outside the ROPE.
You can use Window | Preferences | Tools | Statistical Tools to modify:
- the confidence level (for both the t-test and BEST),
- the Monte Carlo Markov Chain parameters that are used for inference in the Bayesian network described above,
- the ROPE size that defines an interval centered at 0, i.e. 0.2 defines the interval [-0.1, 0.1]