Unit 12

Introduction

Welcome to Week 12 of BIO144!

Course book

This week we will be covering Chapter 12: Review: planning and implementing statistical analyses of the course book.

Code walkthrough

The R code of this week’s chapter is in a code walkthrough script, with a video walkthrough of it. Both are linked at the top of the course book chapter. Work through them before the practical: the last section of the script (“Practical toolbox”) shows code that this week’s practical uses but the chapter does not.

Learning objectives

These learning objectives, together with the content of the course book chapter, define what you need to know for the exam.

After this unit, students will be able to:

  1. Write a planning sentence for a described study, stating the question, the type of response variable, the data structure, the explanatory variables, the planned model and the expected residual degrees of freedom.
  2. Choose a model (linear model, binomial GLM, Poisson GLM, mixed model or ordination) from the type of response variable, the explanatory variables and the data structure of a described study.
  3. Identify the experimental unit in a described study, and recognise pseudoreplication.
  4. Explain the roles of replication, randomisation, controls, blocking and balance in study design.
  5. Count the parameters a planned model will estimate, calculate the expected residual degrees of freedom, and judge whether they are enough.
  6. Explain how sample size affects the precision of estimates and the power of a study, and what a power analysis is for.
  7. Decide which terms to include in a model from the question and the design (variables of interest, planned interactions, design variables, potential confounders), and explain why trying many models or using stepwise selection gives misleading p-values.
  8. Check a fitted model before interpreting it, make explicit predictions from it, and plot the predictions together with the data.
  9. Recognise a report that gives both the statistical result and its biological meaning.

Lecture

Please attend the lecture. If for any reason you can’t, please watch the podcast, which is available on OLAT.

Homework, Practical, and Weekly Quiz

Available here. You will need to be on a UZH network to access this link, so if you are not on campus, you will need to connect to the UZH VPN first.