Lecture6-note - The project A simple study of pine tree...

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1 Bio7 project A statistical study of pine tree needles at UCI Copyright Brigitte Baldi 2006 © The project A simple study of pine tree needles. Learning objectives: Conduct your own field biology project, from beginning to end Apply what you learn in class concretely Apply more than one topic learned in class to a single problem. Your project report is due the last of week in class. It should contain graphs + about 1-2 pages of text & equations ( as a guideline ). Observational study 2 species required Pine needles length Î Is there a difference in mean needle length between the 2 species? Pine trees, cones, and needles Cones Needles Phase 1: Study design & data collection Preliminary study: Explore the factors influencing your response variable in nature Walk around and observe different pine trees Gather a few needles from different parts of a tree Then sit down and think… Define your data collection procedure How many needles, from how many trees, where? Think about why you make those choices How will you ensure the randomness of your samples? Collect data Choose an appropriate sample size ( discussed after midterm ) Be careful to keep the needles in well labeled containers Questions Why would you need to gather more than one needle for each species? What kind of variability do you see when taking a tour of campus? What do you think affects pine needle length? What can you do to average out the effect of confounding variables? How do you plan on designing your study? What will you control for?
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2 Design Number of trees? Trees chosen how? Number of branches? Branches chosen how? Number of needles? Needles chosen how? Species A sample design (same design for species B) Method used to get an SRS Decide on your study design. Æ How many trees, how many branches, how many locations … ? Æ Which choices will be random and which ones will be systematic? Æ What will you do to make sure each sample is a Simple Random Sample? Make a diagram of these choices (look back at chapters 8-9). As with any study / experiment, always always plot your raw data first. Æ What type of graph? Make a graphical summary that can help you describe your sample distributions. Æ What type of graph? Look for unexpected trends or values. If any, try to find out why. Choose an appropriate numerical summary for a comparative graph. Phase 2: Exploratory data analysis Define your hypotheses and select the corresponding statistical test Summarize the whole picture, taking everything into account Conclude __________________ Don’t hesitate to seek help and ask questions Office hours, email, after class All necessary information on the website (Project page) We’ll discuss this project again as we progress through the class Phase 3: Statistical tests / conclusions Scatterplots After plotting two variables on a scatterplot, we describe the relationship by examining the form , direction , and strength of the association. We look for an overall pattern … Form: linear, curved, clusters, no pattern Direction: positive, negative, no direction
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