Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
10.6 Representing variation graphically Teacher notes OCR Biology A Comparing two populations – a statistical approach Specification reference 4.2.2 (f) Learning outcomes After completing the worksheet students should be able to: understand the reasons for selecting statistical routines to analyse data carry out one statistical analysis (t-test) with confidence. Introduction Variation between individuals provides many opportunities for experimental studies. These experimental approaches often generate large amounts of data which need to be analysed. There are a range of methods, graphical and statistical, which can be used in such an analysis. Selecting the correct approach is often an area which causes difficulties for students. Once the appropriate methods have been selected students find it difficult to apply the routines correctly. The aim of this sheet is to explain where each test might be most appropriate, and to give a detailed explanation of one such test. Teacher notes This sheet assumes a knowledge of variation but does not really cover the topic. It is focused more on how to carry out a statistical routine. First list the types of routines commonly encountered, and use the summary table to identify clear features which distinguish when each of the tests are used. The support sheet provides a partially worked example of the students t-test. Work through this with the students. You may choose not to construct a graph depending on time, but it is a useful visual start before approaching the statistics. Discuss the fact that the graph indicates two distinct groups, but cannot provide convincing evidence. The students t-test is approached in a step by step manner. The answers are supplied below to help you support the student. Work through the example either individually or as a class. Finally the exam-style questions are short and approach aspects of the test. Answers Task Graphing the data. Shell Height (cm) Sheltered beach population Exposed beach population 1.51 – 1.75 0 1 1.76 – 2.00 1 3 2.01 – 2.25 1 4 © Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original 1 10.6 Representing variation graphically Teacher notes OCR Biology A Shell Height (cm) Sheltered beach population Exposed beach population 2.26 – 2.50 3 3 2.51 – 2.75 4 2 2.76 – 3.00 3 2 3.01 – 3.25 3 0 3.26 – 3.50 1 0 Graph should show two distinct populations. Table of values. Sheltered beach Number of animals tested (n1) Exposed beach 17 Number of animals tested (n2) 15 Mean ( x 1) 2.76 Mean ( x 2) 2.26 Standard deviation(σ1) 0.374 Standard deviation(σ2) 0.870 Standard deviation squared (σ12) 0.140 Standard deviation squared (σ22) 0.137 t 3.76 degrees of freedom 30 probability of less than 0.001 Questions 1 2 d mean a There is no significant difference between the digit size for the two populations of birds. Any difference is due to chance. b t 2.036 c d degrees of freedom 75 Any two of: the probability is less than 0.05, reject the null hypothesis there is a significant difference between the bird populations the differences are not due to chance. © Oxford University Press 2015 (1 mark) (1 mark) (2 marks) (1 mark) (1 mark) (1 mark) (1 mark) www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original 2