1Stat 13, UCLA, Ivo DinovSlide 1UCLA STAT 13Introduction toStatistical Methods for the Life and Health SciencesInstructor: Ivo Dinov, Asst. Prof. of Statistics and NeurologyTeaching Assistants:Fred Phoa; Anwer Khan & Jason ShenUniversity of California, Los Angeles, Fall 2005http://www.stat.ucla.edu/~dinov/courses_students.htmlStat 13, UCLA, Ivo DinovSlide 2Administrativez The book for this course -- Statistics for the Life Sciences Homework will be primarily assigned from the text You are responsible for keeping up with reading Some chapters will be covered by reading onlyStat 13, UCLA, Ivo DinovSlide 3Survey – Must Complete Anonymouslyzhttp://moodle.stat.ucla.edu/mod/questionnaire/view.php?id=501zhttp://moodle.stat.ucla.edu/ Æ Resources Æ SOCR Æsocrsurvey05 (password) Æ SOCR Intro SurveyPlease complete this anonymous survey ONCE and provide your candid responses1. Logon using any browser: http://moodle.stat.ucla.edu/2. Go to: Resources3. Click on: Statistics Online Computational Resource (SOCR)4. Enter password: socrsurvey055. Click on: SOCR Intro Survey6. Complete the Survey (Thank you!)7. Close BrowserStat 13, UCLA, Ivo DinovSlide 4UCLA STAT 13to just hear is to forgetto see is to rememberto do it yourself is to understand …(… to go to class is to … comprehend …)Stat 13, UCLA, Ivo DinovSlide 5What is Statistics? A practical exampleMichael Benton & Francisco Ayala, Dating the Tree of Life,Science 2003 300: 1698-1700Molecular vs. Paleontological dating of major branching points in the tree of life are debated Molecular date estimates are up to twice as old (due to statistical bias) as Paleontological dates (missing fossils).Goals: Same as that set out by Darwin: to understand where life came from, the shape of evolution,the place of humans in nature and to determine the extent of modern biodiversity and where it is threatened.Stat 13, UCLA, Ivo DinovSlide 6What is Statistics? A practical examplePlants: The first vascular land plants are found as fossils in the Silurian, and earlier evidence from possible vascular plant spores may extend the range back to the Ordovician, 475 Ma considerably < a molecular estimate of 700 Ma.Birds: Molecular estimates place the split of basal cladesand modern orders at 70 to 120 Ma. The oldest uncontroversial fossils of modern bird orders date from the Paleocene (60 Ma), much younger.Mammals: Molecular dates split of modern placentals in the mid- to Late Cretaceous (80 to 100 Ma). The oldest fossil representatives of modern mammals dated from the Paleocene and Eocene (50 to 65 Ma).2Stat 13, UCLA, Ivo DinovSlide 7What is Statistics? Topics!It is proposed that molecular dates are correct (withconfidence intervals) and that methods exist to correct for that error. However, critics have pointed out several pervasive biasesthat make molecular dates too old. First, if calibration dates are too old, then all other dates estimated from them will also be too old.A second biasing factor is that undetected fast-evolving genes could bias estimates of timing. Empirical and statistical studies of vertebrate sequences suggest that such non-clock-like genes may be detected and that they do not affect estimates of dating. However, statistical tests may have low power and could produce consistently > dates. Stat 13, UCLA, Ivo DinovSlide 8What is Statistics? A practical exampleA 3rdsource of bias relates to polymorphism. Two speciesoften become fixed for alternative alleles that existed as apolymorphism in their ancestral species. A 4thbiasing factor is that molecular time estimates show (skewed)asymmetric distributions,with a constrained (largenumbers) younger left-endand an unconstrained (smaller numbers) olderright-end.Stat 13, UCLA, Ivo DinovSlide 9What is Statistics? Estimate Variation!Data Source Metazoa (Animals)In MYA Bilateria (metazoans except sponges, e.g., anemones) Deuterostomia (backboned animals)Gene (8 G) 1200 ± 100 1001 ± 100 Protein (64 E) 930 ± 115 790 ± 60 590 Gene (4 G) 940 ± 80 700 ± 80 Gene (18 G) 670 ± 60 600 ± 60 Gene (22 G) 830 ± 55 Gene (50 G) 1350 ± 150 (est.) 993 ± 46 Gene (22 G) 659 ± 131 Protein (10 E) 627 ± 51 Gene (MtDNA18S rRNA) 588 min. 586/589 min. molecular estimates are that – basal splits among major animal cladeshappened about 1000 MYAStat 13, UCLA, Ivo DinovSlide 10Statistics Examplez What do you think of when you hear “statistics”?z Definition: Statistics is the science of understanding data and making decisions in the face of variability and uncertainty.z To utilize statistics we need to understand: how the data was collected why it was collected how to analyze and interpret the data APPROPRIATELY!Stat 13, UCLA, Ivo DinovSlide 11Newtonian science vs. chaotic sciencezArticle by Robert May, Nature, vol. 411, June 21, 2001zScience we encounter at schools deals with crisp certainties(e.g., prediction of planetary orbits, the periodic table as a descriptor of all elements, equations describing area, volume, velocity, position, etc.)zAs soon as uncertainty comes in the picture it shakes the foundation of the deterministic science, because only probabilistic statements can be made in describing a phenomenon (e.g., roulette wheels, chaotic dynamic weather predictions, Geiger counter, earthquakes, etc.)zWhat is then science all about – describing absolutely certain events and laws alone, or describing more general phenomena in terms of their behavior and chance of occurring? Or may be both!Stat 13, UCLA, Ivo DinovSlide 12Variation in sample percentages50 60 70 80 90Samples of 20 peopleSamples of 500 peopleSample percentageTarget: True populationpercentage = 69%Poll: Do you consider yourselfoverweight? 1010We are getting closer toThe population mean, asis this a coincidence?∞→nComparing percentages from 10 different surveys each of20 people with those from 10 surveys each of500 people (all surveys from same population).3Stat 13, UCLA, Ivo DinovSlide 13Statistics ExampleExample: A plant ecologist measured the growth response of cotton grass (cm) to four different fertilizer treatments in Northern Alaska. For each treatment, five small 4 ft2 plots were selected, all within the particular field of interest.None N(nitrogen) N + P (phosphorus) N+P+K(potassium)NWhat points seem important from this description?Stat 13, UCLA, Ivo DinovSlide 14Statistics ExampleExample (cont’): The data for the experiment were:Fertilizer
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