## 2 Methods
In our study, \"Smoking\", \"Surgery\" (Surgical intervention) and \"Childish\" (Childish diseases) are the least important factors and sperm concentration of males regarding these factors remain in the normal range, but a clear negative trend is observed in Figure 2. Therefore, men with borderline semen quality who wish to have children should quit smoking, and avoid surgical intervention as much as possible. ## 5 Conclusions

In this research, a supervised ensemble learning algorithm (_i.e._, Clustering-Based Decision Forests) is proposed. The proposed algorithm preprocesses the data by removing majority Tomek Links, clustering majority samples into subsets, and bagging the minority samples. Experiment results on real fertility diagnosis dataset have shown that this algorithm outperforms decision trees, support vector machines, random forests, multilayer perceptron neural networks and logistic regression by a noticeable margin. In this study, we also use Clustering-Based Decision Forests to calculate variables' importance scores. The resulting top five important factors affecting semen concentration found in this study are age, serious trauma, sitting time, the season when the semen sample is produced, and high fevers in the last year. This may help to explain the seminal concentration problems in infertile males or set conditions to screen semen donor candidates. Case-control studies are needed to further identify the role of these life habits or health factors in male's semen quality. Due to lack of data, some possible limitations may exist in this research and the major concern refers to sample size. A larger sample size can increase the confidence in the associations observed. Our future research plans to enlarge the datasets to verify the observed relations. ## Acknowledgements

This work was supported in part by the National Natural Science Foundation of China (No.11271374 & No. 61003233). The authors thank all reviewers for their valuable and constructive comments, which greatly improved the quality of this paper. ## Author Contributions

The work presented here was carried out in collaboration between all authors. [PERSON] and [PERSON] defined the research theme; [PERSON] and [PERSON] designed the algorithm; [PERSON] carried out the experiments and analyzed the data; [PERSON] and [PERSON] interpreted the results and wrote the paper. ## Conflicts of Interest

The authors declare no conflict of interest. ## References

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