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)

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

Most recent news and announcements (View all news and announcements for 2009 or for 2008)

2009-01-18. I just released the January 2009 issue of The Monthly Mean. I had set a self-imposed goal of sending out this newsletter between the first and the fifth of every month, but my decision to spend all of Christmas break away from work and my website set my schedule back markedly. I'm hoping to get back on schedule for the February issue.
2009-01-05. I'm switching my bibliography software from EndNote to Zotero. Zotero allows me to more easily capture and store information from the web, but it doesn't yet have the flexibility and customizability of output the EndNote has. I'm going to see if I can get by with a simpler format for my bibliographies on this website. With Zotero, for example, I can't show a link to both the html and pdf versions of a paper. The transition will take a while, but I'm hoping to update and centralize my bibliographies soon.
2008-11-25. The StATS website is back up and running again. The look is somewhat different, so as to match the style of the rest of the Children's Mercy website. The content is pretty much unchanged. They did remove all references to my new website, as is their prerogative. I will gradually correct my links in the new site so that I can link back to all my old content. This will take a while. If you find any errors on my old website (I'm sure you're shocked that Professor Mean would make any errors), please contact me and I'll make the appropriate corrections on the new site.
2008-11-24. I am getting started again on producing illustrated case studies of research ethics. I have a main page for this project and a very early draft of the TGN 1412 trial in PDF format.
2008-11-05. The first issue of the Monthly Mean newsletter was released today. I hope you like it. If you haven't signed up yet, it is easy. I am using a professional service, iContact, so you can be sure that your privacy will be respected and that you will be able to unsubscribe without a lot of hassles.

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

P.Mean: The perils of self-evaluation (created 2009-06-30). A survey by New Scientist magazine examined a phenomenon called "citation amnesia." This is the tendency of researchers to overlook previously published work in the bibliography of their articles. Most of the respondents felt that citation amnesia was a problem. "Indeed, the vast majority of the survey's roughly 550 respondents -- 85% -- said that citation amnesia in the life sciences literature is an already-serious or potentially serious problem. A full 72% of respondents said their own work had been regularly or frequently ignored in the citations list of subsequent publications. Respondents' explanations of the causes range from maliciousness to laziness." There are several problems with this survey, though.
P.Mean: What is the effect of an unmeasured covariate? (created 2009-06-09). Suppose you want to conduct an analysis of covariance, but you have data on some but not all of the covariates. What do you miss out on because of the unmeasured covariate. To understand this, we need to venture in to the world of partitioned matrices.
P.Mean: Institute of Medicine report on conflict of interest (created 2009-05-24). The National Academies Press has announced the release of a report, Conflict of Interest in Medical Research, Education, and Practice, prepared by a special committee of the Institute of Medicine.
P.Mean: Developing a website logo (created 2009-05-22). I'm not big on graphic logos, but the Zotero website asked for one. So I wrote a short R program to create a simple logo.
P.Mean: Data that IRBs should collect about themselves (created 2009-05-22). Somone on the IRBForum (TS) asked about what type of reports that an IRB should provide. There were a lot of good comments. I encouraged a data centric approach to reporting. Here's what I wrote.
P.Mean: Analyzing bad data (created 2009-05-22). A discussion on the MEDSTATS email discussion group centered around a data set involving blood loss. Blood loss was quantified into categories with values of less than 250 ml, 250-500 ml, 500-1000 ml, and great than 1000 ml. The discussion centered on the inefficiencies created when continuous data is reported in categories like these.
P.Mean: NYTimes advice on increasing website traffic (created 2009-05-11). The New York Times has an excellent blog entry on increasing traffic to your website. It is well worth reading if you write a lot of stuff for the web. I had a few additional comments which I added in the comment section of this webpage.
P.Mean: Is this a case-control design (created 2009-04-28). I have a stats study design question. If I were to look at the association of curly hair for instance with a rash on the forehead, I pick a case control study design. When I analyze this I find that 45% of kids in the clinic (surprise) had curly hair. But I look at two groups curly vs non curly and the outcome of interest is the rash on the forehead, instead of cases vs controls so now, has this become an observational study instead of case control? Hope I am making sense, this is only a theoretical question.
P.Mean: Can I use you as a teaching example (created 2009-04-20). I frequently ask people for permission to talk about the projects I am helping them with, as they make great teaching examples. Some people say no, and that's fine. I do offer a discount for paying clients if you let me talk about this work on my web pages. One person raised an important issue when I asked. That person asked me to keep details about his/her organization anonymous if I was illustrating any boneheaded mistakes.

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

Ward A. The role of causal criteria in causal inferences: Bradford Hill's "aspects of association". Epidemiologic Perspectives & Innovations. 2009;6(1):2. Available at: http://www.epi-perspectives.com/content/6/1/2 [Accessed June 24, 2009]. Abstract: As noted by Wesley Salmon and many others, causal concepts are ubiquitous in every branch of theoretical science, in the practical disciplines and in everyday life. In the theoretical and practical sciences especially, people often base claims about causal relations on applications of statistical methods to data. However, the source and type of data place important constraints on the choice of statistical methods as well as on the warrant attributed to the causal claims based on the use of such methods. For example, much of the data used by people interested in making causal claims come from non-experimental, observational studies in which random allocations to treatment and control groups are not present. Thus, one of the most important problems in the social and health sciences concerns making justified causal inferences using non-experimental, observational data. In this paper, I examine one method of justifying such inferences that is especially widespread in epidemiology and the health sciences generally - the use of causal criteria. I argue that while the use of causal criteria is not appropriate for either deductive or inductive inferences, they do have an important role to play in inferences to the best explanation. As such, causal criteria, exemplified by what Bradford Hill referred to as "aspects of [statistical] associations", have an indispensible part to play in the goal of making justified causal claims.
Lazic S, Mason S, Michell A, Barker R. Visualising disease progression on multiple variables with vector plots and path plots. BMC Medical Research Methodology. 2009;9(1):32. Available at: http://www.biomedcentral.com/1471-2288/9/32 [Accessed May 29, 2009]. Description: This paper shows how to use vector plots to display longitudinal changes in individual patients.
SAS Institute. Ten Great Reasons Why A Statistician Should Update to SAS 9.2. Available at: http://support.sas.com/rnd/app/da/stat_top10.html [Accessed May 26, 2009]. Description: I have not used SAS in ten years, but it helps to know what I am missing. The latest version of SAS has generalized linear mixed models, quantile regression, and Markov Chain Monte Carlo solutions for several procedures. SAS has also implemented certain model selection approaches like LAR and LASSO.
American Statistical Association. Making Sense of Statistical Studies. Available at: http://www.amstat.org/education/msss/?nl=0509 [Accessed May 20, 2009]. Excerpt: Are hot dogs unhealthy? What percent of people wear their seat belts when driving? Which works better-a low-fat diet or a low-carbohydrate diet? Would most teenagers return an extra $10 they received in incorrect change at a store? Does listening to music hurt students' concentration and ability to study? How are peoples' heights and foot lengths related? These are just a few examples of the types of questions students will explore in Making Sense of Statistical Studies (MSSS). The module consists of 15 hands-on investigations that provide students with valuable experience in designing and analyzing statistical studies. It is written for an upper middle-school or high-school audience having some background in exploratory data analysis and basic probability.
Gunnes N, Seierstad T, Aamdal S, et al. Assessing quality of life in a randomized clinical trial: Correcting for missing data. BMC Medical Research Methodology. 2009;9(1):28. Available at: http://www.biomedcentral.com/1471-2288/9/28 [Accessed May 20, 2009]. Excerpt: Use of proper methodology developed for analysing data subject to missingness is necessary to reduce potential estimation bias. The quality of life of patients receiving radiation therapy with concurrent chemotherapy (docetaxel) appears somewhat worse than that of patients receiving radiation therapy alone in the period during which treatment is given. The conclusions are robust for the choice of statistical methods.
Mills E, Chan A, Wu P, et al. Design, analysis, and presentation of crossover trials. Trials. 2009;10(1):27. Available at: http://www.trialsjournal.com/content/10/1/27 [Accessed May 20, 2009]. Excerpt: Reports of crossover trials frequently omit important methodological issues in design, analysis, and presentation. Guidelines for the conduct and reporting of crossover trials might improve the conduct and reporting of studies using this important trial design.
Coory M, Wills R, Barnett A. Bayesian versus frequentist statistical inference for investigating a one-off cancer cluster reported to a health depart- ment. BMC Medical Research Methodology. 2009;9(1):30. Available at: http://www.biomedcentral.com/1471-2288/9/30 [Accessed May 19, 2009].
Elhai JD, Calhoun PS, Ford JD. Statistical procedures for analyzing mental health services data. Psychiatry Research. 2008;160(2):129-136. Available at: http://www.ncbi.nlm.nih.gov/pubmed/18585790 [Accessed May 19, 2009].
Flom PL, Cassell DL. Stopping stepwise: Why stepwise and similar selection methods are bad, and what you should use. Available at: http://www.nesug.org/proceedings/nesug07/sa/sa07.pdf [Accessed April 24, 2009].
Moerman C, Deurenberg R, Haafkens J. Locating sex-specific evidence on clinical questions in MEDLINE: a search filter for use on OvidSPTM. BMC Medical Research Methodology. 2009;9(1):25. Available at: http://www.biomedcentral.com/1471-2288/9/25 [Accessed April 16, 2009]. Abstract: Background Many recently published clinical studies report sex-specific data. This information may help to improve clinical decision-making for both sexes, but it is not easily accessible in MEDLINE. The aim of this project was to develop and validate a search filter that would facilitate the retrieval of studies reporting high quality sex-specific data on clinical questions. Methods A filter was developed by screening titles, abstracts and Medical Subject Headings (MeSH) in a set of 80 high quality and relevant papers, 75 of which were identified through a review of clinical guidelines and five through other means. The filter, for use on OvidSPTM, consists of nine command lines for searching free text words in the title, abstract and MeSH of a paper. It was able to identify 74/80 (92.5%) of the articles from which it was derived. The filter was evaluated in a set of 622 recently published original studies on Alzheimer's disease and on asthma. It was validated against a reference of 98 studies from this set, which provided high quality, clinically relevant, sex-specific evidence. Recall and precision were used as performance measures. Results The filter demonstrated 81/98 (83%) recall and 81/125 (65%) precision in retrieving relevant articles on Alzheimer's disease and on asthma. In comparison, only 30/98 (31%) recall would have been achieved if sex-specific MeSH terms only had been used. Conclusion This sex-specific search filter performs well in retrieving relevant papers, while its precision rate is good. It performs better than a search with sex-specific MeSH. The filter can be useful to anyone seeking sex-specific clinical evidence (e.g., guideline organizations, researchers, medical educators, clinicians)
Ethgen M, Boutron I, Steg PG, Roy C, Ravaud P. Quality of reporting internal and external validity data from randomized controlled trials evaluating stents for percutaneous coronary intervention. BMC Medical Research Methodology. 2009;9(1):24. Available at: http://www.biomedcentral.com/1471-2288/9/24 [Accessed April 16, 2009]. Abstract: Background Stents are commonly used to treat patients with coronary artery disease. However, the quality of reporting internal and external validity data in published reports of randomised controlled trials (RCTs) of stents has never been assessed. The objective of our study was to evaluate the quality of reporting internal and external validity data in published reports of RCTs assessing the stents for percutaneous coronary interventions. Methods A systematic literature review was conducted. Reports of RCTs assessing stents for percutaneous coronary interventions indexed in MEDLINE and the Cochrane Central Register of Controlled Trials and published between January 2003 and September 2008 were selected. A standardized abstraction form was used to extract data. All analyses were adjusted for the effect of clustering articles by journal. Results 132 articles were analyzed. The generation of the allocation sequence was adequate in 58.3% of the reports; treatment allocation was concealed in 34.8%. Adequate blinding was reported in one-fifth of the reports. An intention-to-treat analysis was described in 79.5%. The main outcome was a surrogate angiographic endpoint in 47.0%. The volume of interventions per center was described in two reports. Operator expertise was described in five (3.8%) reports. The quality of reporting was better in journals with high impact factors and in journals endorsing the CONSORT statement. Conclusions The current reporting of results of RCTs testing stents needs to be improved to allow readers to appraise the risk of bias and the applicability of the results.
Wuensch K. Stepwise Regression = Voodoo Regression. Available at: http://core.ecu.edu/psyc/wuenschk/StatHelp/Stepwise-Voodoo.htm [Accessed April 16, 2009]. Excerpt: It is pretty cool, but not necessarily very useful, and just plain dangerous in the hands of somebody not well educated in the multiple regression techniques, including effects of collinearity, redundancy, and suppression. Here are some quotes from others I have collected from the now departed STAT-L.
Shahen B. Orwik : The Open Science Platform. Available at: http://orwik.blogspot.com/ [Accessed April 16, 2009].

The most recent personal entries (View all personal entries for 2008 and 2009)

Steve, Cathy, and Nicholas -- Nicholas the scientist (created 2009-04-29). At Nicholas's school, there is an afterschool program called "Science Stars." We weren't sure if Nicholas would like this, but we signed him up. It has been very successful in at least one aspect, he now says it's his favorite part of school. Until recently, his favorite parts of school were either gym or recess. Here are some pictures of Nicholas at Science Stars.
Steve, Cathy, and Nicholas -- Nicholas the traveler, part 1 (created 2009-02-15). Nicholas has always been a very good traveler. He was adopted from Russia, so as a two year old, he got to experience a lot more traveling than many adults.
Steve, Cathy, and Nicholas -- Nicholas the roller blader (created 2009-01-14). During Christmas break, students at Nicholas's school were given a coupon for a free admission to a roller skating session at Skate City. Nicholas loves skating (meaning roller blades, not ice skating). We both took him on December 30, but Steve, having done skating with Nicholas before, wisely decided to let Nicholas do all the skating and he'd do the watching. It's not that I fall down less than Nicholas does, it's that when I fall, it is farther to the ground, and my weight produces greater momentum. Nicholas just picks himself back up and keeps going. Cathy had skated a lot as a child, and rented some skates to go out with Nicholas.
Steve, Cathy, and Nicholas -- Nicholas the artist (created 2008-12-05). Until just recently, Nicholas has not taken a great interest in art projects. There was a recent project, though, that inspired him. The students in his classroom were all asked to color a turkey as a special character. Nicholas chose a Spiderman turkey.

The most popular pages, excluding home page and various archive pages (last checked 2008-11-17)

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 2009-06-30.