P.Mean: Main page for the P.Mean website (created 2008-06-21)

P.Mean Website (created 1997-12-22, reborn at this location 2008-06-21)

News: Sign up for "The Monthly Mean," the newsletter that dares to call itself average, www.pmean.com/news.

Welcome to the P.Mean website. Here are the most important links:

The most recent website entries (View all website entries for 2010, 2009, or 2008)

P.Mean: Using information theory to identify discrepancies within and between text files (created 2010-09-02). I have been experimenting with the use of information theory to identify patterns in text data files. This work in somewhat preliminary, but it has some exciting possibilities. If there are certain patterns that occur frequently at a given column of a text data file (e.g., always the letters "A" or "B"), then these columns become important for looking for aberrant data that might be caused by a typographical error, a misalignment of the row of data, or a deviation from the code book. I want to show some preliminary graphs that illustrate what these patterns look like for some files I am working with. Warning: this is a very large webpage with graphics that extend across dozens of pages!!
P.Mean: Is it ethical to recruit a panhandler that you see on the street into your research study (created 2010-09-01). Someone asked a question about the ethics of approaching a panhandler and sharing information about a research study. I don't know all the details, but apparently, this study was examining veterans of the Iraq war, and this panhandler was holding a sign saying something like please help a veteran of the Iraq war. There was some concern about whether the monetary incentive would be disproportionate for someone who had to beg for a living, or it might be a problem if the panhandler was given money and a flyer about the research study at the same time. I discussed some of my concerns about this study, but it was from the perspective of statistical validity rather than from an ethical perspective.
P.Mean: Pooling different measures of risk in a meta-analysis (created 2010-07-26). Someone on the MEDSTATS email discussion group asked about how to pool results in a meta-analysis where some of the summary measures are reported as odds ratios, others as relative risks, and still others as hazard ratios. There's actually a fourth measure that is commonly used when the outcome measure is binary (live/dead, improved/not improved, relapsed/relapse free, etc.). That is the risk difference, and its inverse, the number needed to treat. Here's what I wrote in response.
P.Mean: What is a Generalized Estimating Equations model? (created 2010-08-19). Generalized Estimating Equations (GEE) are a model for your data that can account for dependence among some of your measurements due to repeated measures, cluster sampling, or a longitudinal data set. It represents an extension of the Generalized Linear Model (GLM). Like the GLM, the GEE model allows you to specify a link function and a mean variance relationship. With the appropriate choice of these two items, you can specify a wide variety of models.
P.Mean: Is Evidence-Based Medicine too rigid (created 2010-08-19). Someone was asking about criticisms of Evidence-Based Medicine (EBM) that the reliance on grading schemes and the hierarchy of evidence was too rigid or was EBM providing some heuristics that could be adapted as needed. This is hard to respond to, but it is an important question. I view checklists and hierarchies as a necessary evil, and that sometimes they are applied too rigidly.
P.Mean: Competing books to the book I am planning to write (created 2010-08-16). I have been asked by several publishers to list competing books to the book I am planning to write. My book is quite different than anything else out there, but perhaps the closest competition would be books that talk about research methods. Here are some possible competitors in that area.
P.Mean: What should clients get from you at the end of the first consulting session (created 2010-08-14). There has been a lot of discussion about the nature and role of consulting on the message boards of the Statistical Consulting section of the American Statistical Association One particularly valuable question was what should you do when starting a new consulting job. Here is an adaptation of one particularly good response.
P.Mean: Glossary for my second book (created 2010-08-11). As I mentioned in an earlier webpage, I am talking to some publishers about writing a second book. Here's a tentative glossary for that book. I'm only including the terms in the glossary for now, but will eventually add definitions.
P.Mean: What's a fair price for SPSS? (created 2010-08-06). There was a discussion on an email discussion group about SPSS about how the SPSS software package was too expensive and how they should consider offering a discount price for the home user. Everyone was in favor of lower prices, of course, and compared the pricing of SPSS to that of Stata and R. In the spirit of debate, I offered a contrarian viewpoint. It also applies to similar complaints I have heard about the pricing of SAS software.
P.Mean: Fighting the claim that any size difference is clinically important (created 2010-08-05). When working with people to select an appropriate sample size, it is important to establish the minimum clinically important difference (MCID). This is a difference such that any value smaller would be clinically trivial, but any value larger would be clinically important. I get told quite often that any difference that might be detected is important. I could be flippant here and then tell them that their sample size is now infinite and my consulting rate is proportional to the sample size, but I don't make flippant comments (out loud, at least). Here's how I might challenge such a claim.
P.Mean: Standard operating procedures for a statistical consulting center (created 2010-07-30). I asked a question on one of the American Statistical Association message boards about how I setting up a consulting service at the University of Missouri-Kansas City (UMKC), where I work part-time. I wanted to develop some SOPs (Standard Operating Procedures) for this center that would supplement the guidance already available on the web. I asked if anyone else had SOPs (or anything similar) that I could look at so I wouldn't re-invent the wheel. I got a lot of responses.

Pages recently receiving major updates

P.Mean: Pilot study (created 1999-09-03, updated 2010-07-08). Dear Professor Mean, I am proposing a research study that will examine a complex intervention of diet, exercise, and behavioral modification for some of my pediatric patients who need to lose weight. I want to collect some data from a pilot study before I start the research study. How do I describe the pilot study in my protocol? -- Sophisticated Sarah
P.Mean: Confidence interval with zero events (created 2001-01-19, updated 2010-07-07). Dear Professor Mean, I was working with a colleague on some confidence intervals for the probability of an adverse event during several different types of operations. One of the proportions was zero, since the event never occurred. My friend computed a confidence interval and it went from zero to zero. I told him that this couldn't be right and computing a confidence interval with zero events is impossible. Isn't that right? -- Killjoy Karlina
P.Mean:: Testing for bimodality (May 3, 2005). This is an update and revision of age on my old site that has some broken links: www.childrensmercy.org/stats/weblog2005/Bimodality.asp. I have talked about bimodality before and it is a rather tricky thing. A recent discussion of tests of bimodality on edstat-l, though, yielded a few promising leads relating to the Dip test of Hartigan.
P.Mean: Design and analysis of pilot studies (created 2004-09-14, updated 2010-07-01). I've corrected a broken link on this article, which was originally published at my old website, www.childrens-mercy.org/stats/weblog2004/PilotStudy.asp. A colleague sent me a very nice paper, Design and analysis of pilot studies: recommendations for good practice. G. A. Lancaster, S. Dodd, P. R. Williamson. J Eval Clin Pract 2004: 10(2); 307-12 that covers some of the same ideas in my web page, Stats: Designing a pilot study. This is a very well researched article and has some excellent recommendations.
P.Mean: Examples of a fishbone diagram (created 2006-03-24). The fishbone diagram (also called the Ishikawa diagram, or the case and effect diagram) is a tool for identifying the root causes of quality problems. It was named after Kaoru Ishikawa, the man who pioneered the use of this chart in quality improvement in the 1960's. Surprisingly, I have had to hunt very hard to find any good examples of a fishbone diagram.
P.Mean: The first three steps in selecting an appropriate sample size (created 2009-07-20). I got an email last week from a client wanting to start a new research project looking at relationships between parenting beliefs and childhood behaviors. The description of the sorts of things to examine was quite elaborate, and it ended with the question "how many families would we need to have any significant differences if they exist?" Unfortunately, all the elaborate information provided did not include the information I would need to answer this question. Justifying a sample size usually involves three steps.

Interesting articles, books, quotes, or websites added to this site recently. (View all interesting articles, books, quotes, and websites for 2010, 2009 or 2008)

Celia Brown, Richard Lilford. The stepped wedge trial design: a systematic review. BMC Medical Research Methodology. 2006;6(1):54. Abstract: "BACKGROUND: Stepped wedge randomised trial designs involve sequential roll-out of an intervention to participants (individuals or clusters) over a number of time periods. By the end of the study, all participants will have received the intervention, although the order in which participants receive the intervention is determined at random. The design is particularly relevant where it is predicted that the intervention will do more good than harm (making a parallel design, in which certain participants do not receive the intervention unethical) and/or where, for logistical, practical or financial reasons, it is impossible to deliver the intervention simultaneously to all participants. Stepped wedge designs offer a number of opportunities for data analysis, particularly for modelling the effect of time on the effectiveness of an intervention. This paper presents a review of 12 studies (or protocols) that use (or plan to use) a stepped wedge design. One aim of the review is to highlight the potential for the stepped wedge design, given its infrequent use to date. METHODS: Comprehensive literature review of studies or protocols using a stepped wedge design. Data were extracted from the studies in three categories for subsequent consideration: study information (epidemiology, intervention, number of participants), reasons for using a stepped wedge design and methods of data analysis. RESULTS: The 12 studies included in this review describe evaluations of a wide range of interventions, across different diseases in different settings. However the stepped wedge design appears to have found a niche for evaluating interventions in developing countries, specifically those concerned with HIV. There were few consistent motivations for employing a stepped wedge design or methods of data analysis across studies. The methodological descriptions of stepped wedge studies, including methods of randomisation, sample size calculations and methods of analysis, are not always complete. CONCLUSION: While the stepped wedge design offers a number of opportunities for use in future evaluations, a more consistent approach to reporting and data analysis is required." [Accessed September 1, 2010]. Available at: http://www.biomedcentral.com/1471-2288/6/54.
Michael A Hussey, James P Hughes. Design and analysis of stepped wedge cluster randomized trials. Contemp Clin Trials. 2007;28(2):182-191. Abstract: "Cluster randomized trials (CRT) are often used to evaluate therapies or interventions in situations where individual randomization is not possible or not desirable for logistic, financial or ethical reasons. While a significant and rapidly growing body of literature exists on CRTs utilizing a "parallel" design (i.e. I clusters randomized to each treatment), only a few examples of CRTs using crossover designs have been described. In this article we discuss the design and analysis of a particular type of crossover CRT - the stepped wedge - and provide an example of its use." [Accessed September 1, 2010]. Available at: http://faculty.washington.edu/peterg/Vaccine2006/articles/HusseyHughes.2007.pdf.
Keith A. McGuinness. Of rowing boats, ocean liners and tests of the ANOVA homogeneity of variance assumption. Austral Ecology. 2008;27(6):681-688. Abstract: "One of the assumptions of analysis of variance (ANOVA) is that the variances of the groups being compared are approximately equal. This assumption is routinely checked before doing an analysis, although some workers consider ANOVA robust and do not bother and others avoid parametric procedures entirely. Two of the more commonly used heterogeneity tests are Bartlett's and Cochran's, although, as for most of these tests, they may well be more sensitive to violations of the ANOVA assumptions than is ANOVA itself. Simulations were used to examine how well these two tests protected ANOVA against the problems created by variance heterogeneity. Although Cochran's test performed a little better than Bartlett's, both tests performed poorly, frequently disallowing perfectly valid analyses. Recommendations are made about how to proceed, given these results." [Accessed August 19, 2010]. Available at: http://onlinelibrary.wiley.com/doi/10.1111/j.1442-9993.2002.tb00217.x/abstract.
Patricia Keith-Spiegel, Joan Sieber, Gerald P. Koocher. Responding to Research Wrongdoing : A User Friendly Guide. Excerpt: "Every once in awhile a product comes along that is destined to make a difference. This Guide is such a product. Informed by data generated through surveys and interviews involving more than 2,000 scientists, the Guide gives voice to those researchers willing, some with eagerness and others with relief, to share their stories publicly in their own words. There are stories from scientists who want to do the right thing, but are unsure how to go about it or concerned about negative consequences for them or their junior colleagues. There are accounts from researchers who took action, and are keen to share their successful strategies with others. On the flip side, there are those who hesitated and now lament not having guidance that might have altered the course of past events." [Accessed August 14, 2010]. Available at: http://www.ethicsresearch.com/images/RRW_7-17-10.pdf.
Gerald P. Koocher, Patricia Keith-Spiegel. Peers nip misconduct in the bud. Nature. 2010;466(7305):438-440. Excerpt: "What do researchers do when they suspect a colleague of cutting corners, not declaring a conflict of interest, neglecting proper oversight of research assistants or 'cooking' data? In one study1, almost all said that they would personally intervene if they viewed an act as unethical, especially if it seemed minor and the offender had no history of infractions." [Accessed August 14, 2010]. Available at: http://www.ethicsresearch.com/images/Nature_Opinion_-_Koocher_Keith-Spiegel.pdf.
M. Castillo. Authorship and Bylines. American Journal of Neuroradiology. 2009;30(8):1455-1456. Excerpt: "From the ancient Greeks to Shakespeare, the question of authorship often arises. The issue of appropriate article authorshiphas always been of special interest to editors of scientific journals. In the biomedical sciences, as the complexity and funding of published studies increases, so does the length of the byline. Although a previous American Journal of Neuroradiology Editor-in-Chief already addressed this issue, I think it is time to revisit it.1 From my own experience, articles can be categorized according to the number of authors as follows: fewer than 2 authors (Editorials, Commentaries, Letters), fewer than 5 authors (Case Reports and Technical Notes), 5�10 authors (retrospective full-length articles), 10�15 (prospective, often grant-funded articles), more than 15 authors (reports of task forces, white papers, etc). Among so many authors, it is not uncommon to find individuals whose contributions are minimal and many times questionable. Who actually did enough work to be listed as an author? In other words, who can claim ownership rights in a particular intellectual property?" [Accessed August 14, 2010]. Available at: http://www.ajnr.org/cgi/reprint/ajnr.A1636v1.pdf.
R A Parker. Estimating the value of an internal biostatistical consulting service. Stat Med. 2000;19(16):2131-2145. Abstract: "Biostatistical consulting is a service business. Although a consulting biostatistician's goal is long-term collaborative relationships with investigators, this is the same as the long-term goal of any business: having a group of contented, satisfied customers. In this era of constrained resources, we must be able to demonstrate that the benefit a biostatistical consulting group provides to its organization exceeds its actual cost to the institution. In this paper, I provide both a theoretical framework for assessing the value of a biostatistical service and provide an ad hoc method to value the contribution of a biostatistical service to a grant. Using the methods described, our biostatistics group returns more than $6 for each dollar spent on institutional support in 1998." [Accessed August 14, 2010]. Available at: http://www.ncbi.nlm.nih.gov/pubmed/10931516.
Richard Horton, Richard Smith. Time to redefine authorship. BMJ. 1996;312(7033):723. Excerpt: "Physicists do it by the hundred; scientists do it in groups; fiction writers mostly alone. And medical researchers? Rarely now do they write papers alone, and the number of authors on papers is increasing steadily.1 Under pressure from molecular biologists, the National Library of Medicine in Washington is planning to list not just the first six authors in Index Medicus but the first 24 plus the last author.2 Notions of authorship are clearly in the eye of the beholder, and many authors on modern papers seem to have made only a minimal contribution.3 4 5 Few authors on modern multidisciplinary medical papers fit the 19th century notion of taking full responsibility for every word and thought included, and yet the cumbersome definition of authorship produced by the International Committee of Medical Journal Editors (the Vancouver Group) is based on that concept.6 The definition produced by editors seems to be out of touch with what is happening in the real world of research, and researchers and editors need to consider a new definition. The BMJ, Lancet, University of Nottingham, and Locknet (a network to encourage research into peer review7) are therefore organising a one day meeting on 6 June in Nottingham to consider the need for a new definition. All the members of the Vancouver Group will be there, and everybody is welcome." [Accessed August 14, 2010]. Available at: http://www.bmj.com/cgi/content/full/312/7033/723.
R A Parker, N G Berman. Criteria for authorship for statisticians in medical papers. Stat Med. 1998;17(20):2289-2299. We organize a statistician's potential scientific and intellectual contributions to a medical study into three types of activities relating to design, implementation and analysis. For each type, we describe high-level, mid-level and low-level contributions. Using this framework, we develop a point system to assess whether authorship is justified. Although we recommend discussion and resolution of authorship issues early in the course of any project, our system is especially useful when this has not been done. [Accessed August 14, 2010]. Available at: http://www.ncbi.nlm.nih.gov/pubmed/9819828.
LiquidPub. Liquid Publications: Scientific Publications meet the Web. Excerpt: "The LiquidPub project proposes a paradigm shift in the way scientific knowledge is created, disseminated, evaluated and maintained. This shift is enabled by the notion of Liquid Publications, which are evolutionary, collaborative, and composable scientific contributions. Many Liquid Publication concepts are based on a parallel between scientific knowledge artifacts and software artifacts, and hence on lessons learned in (agile, collaborative, open source) software development, as well as on lessons learned from Web 2.0 in terms of collaborative evaluation of knowledge artifacts." [Accessed August 10, 2010]. Available at: http://project.liquidpub.org/.

The most recent personal entries (View all personal entries)

Steve, Cathy, and Nicholas -- Nicholas shoots some pictures for his "me collage" (created 2010-08-29). One of Nicholas's first homework assignments was to cut out some pictures from magazines and newspapers that could be combined into a "me collage." This would go on his writing binder and when Nicholas was out of ideas for writing assignments, his teacher could point to one of the pictures in the collage and suggest that he write about that. Nicholas and Cathy took some pictures with our digital camera to supplement the ones he found in the newspaper. Here are those pictures.
Steve, Cathy, and Nicholas -- Nicholas goes whale watching (created 2010-07-08). While in Juneau, we took a whale watching cruise. Here are some pictures of a humpback whale and other wildlife that we encountered during the cruise.
Steve, Cathy, and Nicholas -- Nicholas carries a big chunk of the Mendenhall glacier (created 2010-07-08). While in Juneau, we took a bus tour to Mendenhall Glacier. It was the first glacier that I saw on our Alaska tour, and it was quite impressive. Pieces of the glacier had fallen off into Mendenhall Lake and Nicholas found one that had drifted ashore. At first, I told Nicholas that he needed to leave the chunk of ice right there. But then we found that the park rangers had taken another chunk of ice from the lake and were displaying it near the visitors center. So Nicholas wanted to bring them his own chunk of ice.
Steve, Cathy, and Nicholas -- Letters I've written to the Kansas City Star (created 2010-07-02). One of my goals in life is to get a letter published on the Opinion pages of the Kansas City Star on a regular basis. They don't like to publish from any one writer more often than once a month. So far I've had mixed success, but I thought it would be interesting to post all of these letters on my website, both the ones that got published and the ones that didn't. I tried to note which efforts were successful and which were not, but I may not be 100% accurate.
Steve, Cathy, and Nicholas -- Nick makes his own Father's Day card (created 2010-07-01). We were on vacation in Alaska during Father's Day and I'm just getting around to posting various pictures of the trip. One thing unrelated to Alaska, but still worth showing is the Father's Day card that Nicholas made for me.
Steve, Cathy, and Nicholas -- Pictures of the Back Porch Cloggers (created 2010-06-08). In January of 2000, I took lessons on Appalachian Clogging from a group called the Back Porch Cloggers. I persisted through the entire fifteen weeks, graduated and then took the beginning courses a second time as well as continuing with the advanced group. Eventually, I got good enough that I was invited to be part of the performing group. The performing group would go monthly to various locations such as local festivals and to nursing homes and perform some of the more advanced dances. The leader of the Back Porch Clogges, John Hardin, retired in 2006, but the members of the group still kept meeting irregularly to keep practicing the dances so we wouldn't forget them. We also found time to hold several performances at the Deanna Rose Children's Farmstead. We do a few dances and then invite the children up (and any brave adults) to practice a few very simple clogging steps. Here are some pictures from a performance last year. I'll try to identify all the dancers, but will not name anyone who is hidden behind another dancer.

The most popular pages, excluding home page and various archive pages (last checked 2009-12-06)

This work is licensed under a Creative Commons Attribution 3.0 United States License. This page was written by Steve Simon and was last modified on 2010-09-02.