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The validity and practical utility of observational medical research depends critically on good study design, excellent data quality, appropriate statistical methods and accurate interpretation of results. Statistical methodology has seen substantial development in recent times. Unfortunately, many of these methodological developments are ignored in practice. Consequently, design and analysis of observational studies often exhibit serious weaknesses. The lack of guidance on vital practical issues discourages many applied researchers from using more sophisticated and possibly more appropriate methods when analyzing observational studies. Furthermore, many analyses are conducted by researchers with a relatively weak statistical background and limited experience in using statistical methodology and software. Consequently, even 'standard' analyses reported in the medical literature are often flawed, casting doubt on their results and conclusions. An efficient way to help researchers to keep up with recent methodological developments is to develop guidance documents that are spread to the research community at large. These observations led to the initiation of the strengthening analytical thinking for observational studies (STRATOS) initiative, a large collaboration of experts in many different areas of biostatistical research. The objective of STRATOS is to provide accessible and accurate guidance in the design and analysis of observational studies. The guidance is intended for applied statisticians and other data analysts with varying levels of statistical education, experience and interests. In this article, we introduce the STRATOS initiative and its main aims, present the need for guidance documents and outline the planned approach and progress so far. We encourage other biostatisticians to become involved.

We have studied the activity of recombinant human gamma-interferon and recombinant human tumor necrosis factor alpha against four human ovarian cancer i.p. xenografts OS, LA, HN, and DO derived from primary tumor material. In the OS xenograft all control mice died by 42 days and therapy starting 7 days after tumor cell injection with 5 X 10(4) units recombinant human gamma-interferon or 1 microgram recombinant human tumor necrosis factor alpha alone had no significant effect on cumulative survival in three separate experiments. However, a combination of the two agents resulted in 85% cumulative survival at 150 days. This combination therapy also significantly increased survival of mice treated as late as 21 days after tumor cell injection. In the LA xenograft (where control mice were all dead by 23 days) therapy with either agent alone, or a combination, more than doubled survival time of mice. In the HN xenograft all control mice were dead at 22 days whereas either therapy alone or in combination gave +85% cumulative survival at 100 days. In a fourth xenograft, DO, survival of mice in the combination therapy group was significantly increased. Thus these two biological therapies, alone or in combination, show significant activity against human ovarian cancer cells.