Here we would like to clarify what we consider a misunderstanding of our concept of robustness [1] and how the lack of robust approaches led to misleading and unsound claims about the absence of climate change in East African Highlands [2,3,4]. We defined robustness as [1, p.32]: "... the confidence in the certainty of one’s result, given that assumptions about such phenomenon might be wrong or untestable, [robustness] can be evaluated through the agreement of results obtained with different methods or with different models used to analyze the data". This well-known epistemological principle can be viewed as the need to support inferences with methods relying on diverse assumptions, as proposed by Levins [5,6]. Because inferences on the lack of warming in East African Highlands were based exclusively on "the Dickey Fuller regression", this approach was absent from previous publications on the topic [2,3,4], as acknowledged by Stern et al. [7]. As we showed in figure 1 of our article [1, p.34], increasing temperature trends can be observed with four different methods from time series analysis for the 1966-1996 period in the grid containing Kericho [from CRUTS 2.1], meaning that our claim about the existence of temperature trends was not an artifact due to the use of a specific method for time series analysis. In that sense, the conclusions about the existence of temperature warming presented in Stern et al. [7], can only be considered robust in light of the results presented elsewhere, for example [1,8].
We would also like to clarify the inaccurate attribution of judgments not presented in our work [1], claimed in [7] from which we quote: “Chaves and Koenraadt [1] claim (incorrectly) that, because only one test - the Q test [reference in 2] - was used to test for serial correlation in the residuals, the procedures used by Hay et al. [2] were not robust." In our piece in the Quarterly Review of Biology we specifically expressed the following concern regarding analyses presented in earlier work [2,3,4], see [1, p. 33]: “The aforementioned studies did not find statistically significant results for deterministic or random trends; however, error assumptions were not tested adequately. Only one portmanteau test for general serial correlation was performed, whereas autocorrelation should be tested for several time lags." Our comment clearly highlighted ""the need for testing temporal autocorrelations for several time lags"", a flaw still present in [7] and a standard procedure in time series analysis [9]. We recognize the effort of Stern et al. [7] to highlight differences in the CRU datasets and the unreliability of Dickey-fuller regression as a tool to find trends in time series analysis (further elaborated in the previous comment by Pascual and Rodo [10]), and, more importantly, to mend unsubstantiated inferences on the lack of increasing temperature trends [2,3,4] in a region that has undergone undeniable signatures of warming [8]. This represents a major advance towards more solid approaches to understand the role of climate on malaria transmission dynamics. Although, decreasing trends in malaria time series have been reported recently [11,12,13], and probably reflect the transient success of malaria control strategies, the demonstrated sensitivity of malaria transmission dynamics to climate [14,15], is a warning about the need to better understand links between climate and malaria. As we highlighted in our Quarterly Review of Biology contribution [1, Table 2, p.38-41], many unknowns plague our understanding of the impact of a changing environment on the different aspects of malaria transmission. This knowledge may prove invaluable to minimize the impact of surprises arising during the implementation of malaria elimination agendas that dismiss the importance of climate on malaria transmission.

Luis Fernando Chaves
Hokkaido University, Japan

Constantianus J. M. Koenraadt
Wageningen University, The Netherlands

References

1. Chaves LF, Koenraadt CJM (2010) Climate Change and Highland Malaria: Fresh Air for a Hot Debate. The Quarterly Review of Biology 85: 27-55.
2. Hay SI, Cox J, Rogers DJ, Randolph SE, Stern DI, et al. (2002) Climate change and the resurgence of malaria in the East African highlands. Nature 415: 905 - 909.
3. Shanks GD, Hay SI, Stern DI, Biomndo K, Snow RW (2002) Meteorologic influences on Plasmodium falciparum malaria in the highland tea estates of Kericho, western Kenya. Emerging Infectious Diseases 8: 1404-1408.
4. Small J, Goetz SJ, Hay SI (2003) Climatic suitability for malaria transmission in Africa, 1911–1995. Proceedings of the National Academy of Sciences 100: 15341-15345.
5. Levins R (1968) Evolution in Changing Environments. Some theoretical explorations. Princeton: Princeton University Press. 120 p.
6. Levins R (2006) Strategies of abstraction. Biology & Philosophy 21: 741-755.
7. Stern DI, Gething PW, Kabaria CW, Temperley WH, Noor AM, et al. (2011) Temperature and Malaria Trends in Highland East Africa. PLoS ONE 6: e24524.
8. Thomson MC, Connor SJ, Zebiak SE, Jancloes M, Mihretie A (2011) Africa needs climate data to fight disease. Nature 471: 440-442.
9. Shumway RH, Stoffer DS (2000) Time series analysis and its applications: New York: Springer. 572 p.
10. Pascual M, Rodo X (2011) Some lessons learnt from the debate on temperature trends and highland malaria. PLoS ONE 6: e24524.
11. Zhou G, Afrane YA, Vardo-Zalik AM, Atieli H, Zhong D, et al. (2011) Changing Patterns of Malaria Epidemiology between 2002 and 2010 in Western Kenya: The Fall and Rise of Malaria. PLoS ONE 6: e20318.
12. John CC, Riedesel MA, Magak NG, Lindblade KA, Menge DM, et al. (2009) Possible Interruption of Malaria Transmission, Highland Kenya, 2007-2008. Emerging Infectious Diseases 15: 1917-1924.
13. Chaves LF, Hashizume M, Satake A, Minakawa N (2011) Regime shifts and heterogeneous trends in malaria time series from Western Kenya Highlands. Parasitology 138: in press.
14. Childs DZ, Boots M (2010) The interaction of seasonal forcing and immunity and the resonance dynamics of malaria. Journal of the Royal Society Interface 7: 309-319.
15. Alonso D, Bouma MJ, Pascual M (2011) Epidemic malaria and warmer temperatures in recent decades in an East African highland. Proceedings of the Royal Society B: Biological Sciences 278: 1661-1669.