Statistical Reasoning and Analysis Tony Panzarella Department of Biostatistics Princess Margaret Cancer Center  Tony.Panzarella@uhnres.utoronto.ca September 2014

“Lies, damned lies, and statistics” (British Prime Minister Benjamin Disraeli,1804–1881) “Talked politics, scandal, and the three classes of witnesses—liars, d—d liars, and experts.” (The Life and Letters of Thomas Henry Huxley by L. Huxley, 1900) https://en.wikipedia.org/wiki/Lies,_damned_lies,_and_statistics

Statistics – the new Sexy!? Hal Varian, Google's chief economist, says statistician will be 'the sexy job in the next 10 years.' Chad Schafer explains why. (August 4, 2013, Daniel Marsula/Post-Gazette) http://www.post-gazette.com/opinion/Op-Ed/2013/08/04/The-Next-Page-Data-Driven-Why-statistics-is-sexy/stories/201308040172#ixzz3CFcEr9IV Google’s prediction: What will be the "sexy" job in the next ten years? Here’s a strange prediction from Google’s Chief Economist: “I keep saying that the sexy job in the next 10 years will be statisticians. And I’m not kidding.”

Some Keywords Study Designs, Confounding Pitfalls of Data Analysis Bias (representative sampling, statistical assumptions) Errors in methodology (statistical power, multiple comparisons, measurement error) Interpretation (precision and accuracy, causality, graphical representation) Era of Big Data

Prelude: Design and Analysis Objective: Design the ultimate Intro to PHS talk… and the worst one that I can still get away with… Methods: Identify topic(s), and delivery with visuals Examples; No formula Take-home messages

Correlations, Cluster analysis Source: Sebastian Wernicke, 2010, TedTalks

Nonparametric methods using ranks, Discriminant analysis Source: Sebastian Wernicke, 2010, TedTalks

Confidence Intervals, Associations, Time-to-event analysis Source: Sebastian Wernicke, 2010, TedTalks

Data Mining, Pattern Recognitions Source: Sebastian Wernicke, 2010, TedTalks

Pattern Recognitions (Evidence….Hans Rolling) Source: Sebastian Wernicke, 2010, TedTalks Hans Rolling “The best stats you’ve ever seen, New insights on poverty)

Motivating Example: Smoking & Survival 20-year follow-up study, Wickham in UK (Tunbridge et al. 1977) 1972-1974, one-in-six survey of the electoral roll, largely concerned with thyroid disease and heart disease For simplicity, consider women aged 45 to 75 at the start of the study Smoking status: current smoker (Y/N) 20-year survival info: determined for all women in the study

Smoking & Survival (Cont’d) Protective effect of smoking? (data adapted from Appleton et al. 1996, Am. Stat.)

Smoking & Survival (Con’t) Consider 10-year ranges: 45-54,55-64,65-75 Non-smoking group does better in each case!

Gender Bias, or Not? 1973, UC Berkeley was sued for discrimination against women in graduate school admissions Percent acceptance: Male vs Female, 44% vs. 35%

Gender Bias, or Not? (cont’d) P. J. Bickel, E. A. Hammel, J. W. O'Connell. (1975). Sex Bias in Graduate Admissions: Data from Berkeley. Science 187, (4175). pp. 398-404

Message #1 Be aware of the dangers of ignoring a covariate that is correlated to an outcome variable and an explanatory one. Simpson, E.H. (1951). “The interpretation of Interaction in Contingency Tables”, Journal of the Royal Statistical Society, B, 13, 238-241. Simpson’s Paradox; many other examples

Guard Against Biases

Biases due to … Selection of subjects: web surveys Responses: e.g. question on income Contamination in controls: non-blind study Recall: food-intake Attrition: drop out Reporting: negative findings Publication: meta-analysis Over thirty kinds of biases

Guard Against Biases [BACKUP REFERENCE] Bias in design Concato et al (2001). A nested case–control study of the effectiveness of screening for prostate cancer: research design Concato et al. (2001) reports another type of bias in designs for prostate cancer detection when groups were asymptomatic men who received digital rectal examination, screening by prostate specific antigen and transrectal ultrasound, but there was no ‘control’ group with ‘no screening’. Thus the effectiveness of screening could not be evaluated. Although prostate-specific antigen (PSA) and digital rectal examination (DRE) are commonly used to screen for prostate cancer, available data do not confirm that either test improves survival. This report describes the methodological aspects of a nested case–control study addressing the question of whether PSA screening, with or without DRE, is effective in increasing survival. Potential sources of bias are discussed, as well as corresponding strategies used to avoid them

Possible steps to minimize bias Assess the validity of the identified target population, and the groups to be included in the study in the context of objectives and the methodology. Evaluate the reliability & validity of the measurements required to assess the antecedents and outcomes, also other tools you plan to deploy. Carry out a pilot study and pretest the tools. Make changes as needed. Identify possible confounding factors and other sources of bias; develop an appropriate design that can take care of most of these biases. Use matching, blinding, masking, and random allocation as needed. Analyze the data with proper statistical methods. Use standardized or adjusted rates where needed, do the stratified analysis, or use mathematical models such as regression to take care of biases that could not be ruled out by design. Report only the evidence based the results – enthusiastically but dispassionately

Multiple Testing (Large p & small n)

Data Dredging

“Deming, data and observational studies: a process out of control and needing fixing” Young and Karr (2011) Significance, p116-120.

“Deming, data and observational studies: a process out of control and needing fixing”

Deming, data and observational studies: a process out of control and needing fixing” Young and Karr (2011). Significance, p116-120 Young, S. S. and Yu, M. (2009) To the Editor. Journal of the American Medical Association, 301, 720–721.

Visual Display of Quantitative Information Effectiveness of traffic enforcement in 1955-6, Before vs. After Source (Tufte, 1983)

In the Age of BIG Data Does Big Data make Statistics obsolete? NO! BIG data, Big mistake? (Google Flu) http://www.ft.com/cms/s/2/21a6e7d8-b479-11e3-a09a-00144feabdc0.html#axzz3CHWGduc7

Statistical Truisms Correlation does not imply Causation In fact, causal relationships are among the most significant discoveries from big data that analytics practitioners seek. Finding causes to observed effects would truly be a gold mine of value for any business, science, government, healthcare, or security group that is analyzing big data. Sample variance does not go to zero, even with Big Data

Statistical Truisms (cont’d) Sample bias does not necessarily go to zero, even with Big Data  Sample bias can lead to models with biased results, slanted against the wonderful diversity of the original population Absence of Evidence is not the same as Evidence of Absence  Reference: http://www.amstat.org/publications/jse/v10n3/chance.html 

Acknowledgements Prof. Wendy Lou

Q & A