Abstract: . . .  have contributed to the relative scarcity of evaluation studies that employ time series, at least in the domain of the social sciences 11 . 11 A prototypical example of a research design tailored to the analysis of time-series is a study by Bullinger (1989). This study does not, however, deal with the evaluation of interventions, but rather investigates the effects of atmosphere pollutants and weather factors on psychological Page 27 Joachim Schahn and Gerd Bohner 27 4. Tabular summary All the problems mentioned in section II, as well as possible solutions or controls, are summarized in keywords in . . .
. . .  phase, it is more advisable to average the data in order to enhance their reliability (Schahn and Bohner 1993). These reasons may have contributed to the relative scarcity of evaluation studies that employ time series, at least in the domain of the social sciences 11 . 11 A prototypical example of a research design tailored to the analysis of time-series is a study by Bullinger (1989). This study does not, however, deal with the evaluation of interventions, but rather investigates the effects of atmosphere pollutants and weather factors on psychological Page 27 Joachim Schahn and Gerd Bohner 27 . . .
. . .  interviews. Sometimes this method is preferred for reasons of economy even if observation is possible in principle but involves high effort. In this context, concerns about the credibility of collected responses arise. It is often insinuated that participants are aware of the research question (e.g., environmentally relevant behavior), that a norm to behave in an ecologically responsible manner becomes activated, and that answers are shifted in this direction: thus, answers are "distorted" in a direction that is perceived as "socially desirable" . This argument is often set forth as a case against . . .
. . .  and SocioFile carried out in 1995 and updated in 1998. Page 6 6 Evaluation Research: Methodological Aspects Research questions in the field of environmental protection form only part of the topics usually summarized under the notion " environmental psychology "; furthermore, they can also be found in sociology, educational sciences and economics. Therefore, for the purpose of this article we use the notion " environmental research in the social sciences" without differentiation between the various disciplines. This research is defined predominantly by its topic; the theories and methods that are . . .
. . .  3. Treatment contamination - Problematic only if treatment effects fail to appear - control group interviews 4. Constancy of treatment - Checks of quality and quantity of treatment ("manipulation check") 5. Different baseline values of groups under investigation - Computation of a priori differences and consideration in interpretation (minimal solution) - multiple pretests - attempts to replicate - control of confounding variables (statistically or by "matching") - "multiple baseline design", i.e. delayed repetition of treatment in at least 3 samples 6. Persistence of effe . . .
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