Association Rules - Data Mining for the Masses - page 86

Figure 5-10. Chaning the confidence percent threshold.
Figure 5-11. Four rules found with the 50% confidence threshold.
14) Eureka! We have found rules, and our hunch that Religious, Family and Hobby
organizations are related was correct (remember Figure 5-7). Look at rule number four. It
just barely missed being considered a rule with an 80% confidence threshold at 79.6%.
Our other associations have lower confidence percentages, but are still quite good. We can
see that for each of these four rules, more than 20% of the observations in our data set
support them. Remember that since support is not reciprocal, the support percents for
rules 1 and 3 are the same, as they are for rules 2 and 4. As the premises and conclusions
were reversed, their confidence percentages did vary however. Had we set our confidence
percent threshold at .55 (or 55% percent), rule 1 would drop out of our results, so Family
→ Religious would be a rule but Religious → Family would not. The other calculations to
the right (LaPlace…Conviction) are additional arithmetic indicators of the strength of the
rules' relationships. As you compare these values to support and confidence percents, you
will see that they track fairly consistently with one another.