Cambridge Pre-U Syllabus - Cambridge International Examinations

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64 Notes on the use of statistics in Biology Cambridge Pre-U Draft Candidates should know the distinction between descriptive statistics and statistical tests. They should also appreciate the requirement to choose appropriate statistical methods before planning an investigation in which they will either collect primary data or analyse secondary data. Candidates should have an understanding of the different types of variable and also the different types of data that they may collect or be asked to analyse. These are: Type of variable Type of data Qualitative Categoric Nominal Ordered Ordinal (ranked) Quantitative Continuous Interval (having any value, e.g. 1.0, 2.5, etc.) Discrete Interval (integers only, e.g. 1, 2, 3, etc.) For quantitative data, candidates should understand the difference between a normal distribution and a distribution that is non-normal. Candidates should know appropriate descriptive statistical methods to simplify their data. They should be able to use a calculator and/or spreadsheet program to find the mean, median, mode, total range, interquartile range, standard deviation, standard error and 95%CI. Standard error and 95%CI are useful for expressing the reliability of an estimate of the mean and for putting error bars on graphs. Candidates should understand how to apply these methods and explain their significance for their own data and any given data. Candidates should know when it is appropriate to use a statistical test. They should be able to use statistical tests to test for an association and when to test for the significance of differences between samples. The chisquared (χ 2 ) test is used to test the difference between observed and expected frequencies of nominal data. The chi-squared test allows the evaluation of the results of breeding experiments and ecological sampling. The t-test is of value in much of Biology to test for the significance of differences between samples. Candidates should be able to use Pearson’s linear correlation to test for a correlation between two sets of normally-distributed data and Spearman’s rank correlation to test for a correlation between two sets of data that are not distributed normally. They should know that a correlation does not necessarily imply a causative relationship. These statistical methods are dealt with fully in many books and web sites on statistics for Biology. Candidates are not expected to remember the following equations and symbols. They are expected to be able to use the equations to calculate standard deviations and standard errors (which they may use for error bars on graphs), to test for significant differences between the means of two small unpaired samples and to perform a chi-squared test on suitable data from genetics or ecology. Candidates will be given access to the equations, the meanings of the symbols, a t-table and a chi-squared table. In both the t-test and the chisquared test they should be able to calculate the number of degrees of freedom without any reminders. They should appreciate levels of significance and use calculated (or given) values of t and χ 2 to make appropriate conclusions.
Cambridge Pre-U Syllabus standard deviation standard error t-test χ 2 test Key to symbols S s = M = 2 Σ( x − x) n −1 s n 1 2 x − x t = v = n1 + n2 – 2 ⎛ 2 2 ⎞ ⎜ s s 1 2 ⎟ ⎜ + ⎟ ⎜ n1 n2 ⎟ ⎝ ⎠ 2 ( O − E) 2 χ = Σ v = c – 1 E s = standard deviation x = mean SM= standard error c = number of classes Σ= ‘sum of ’ n = sample size (number of observations) O = observed ‘value' x = observation v = degrees of freedom E = expected ‘value' Candidates should note that, on some calculators, the symbol σ may appear instead of the symbol s. Candidates are not expected to appreciate the difference between sn(σ n) and sn–1 (σ n–1). χ 2 tests will only be expected on one row of data. Questions involving the use of descriptive statistics and the statistical tests described above may be set on Components 1, 2 and 3. The use of a spreadsheet to collate, analyse and present data from an individual or group study could form part of the Optional Formative Assessment. Electronic calculators will be allowed in the examination, subject to the CIE general regulations. 65
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Cambridge Pre-U Syllabus - DRAFT Su
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2 © University of Cambridge Intern
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4 Introduction Cambridge Pre-U Draf
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6 Aims The course aims to: Cambridg
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8 Assessment objectives Cambridge P
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10 Description of Papers Cambridge
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12 Curriculum Content The syllabus
Page 16 and 17: 14 Cambridge Pre-U Draft In the con
Page 18 and 19: 16 1.1 Eukaryotic cell structure Co
Page 20 and 21: 18 1.3 Cell replication Content DNA
Page 22 and 23: 20 1.5 Respiration Content ATP Chem
Page 24 and 25: 22 Cambridge Pre-U Draft Practical
Page 26 and 27: 24 2. THE ORIGIN AND EVOLUTION OF L
Page 28 and 29: 26 2.3 The evolution of life Conten
Page 30 and 31: 28 3. ANIMAL PHYSIOLOGY Section 3 (
Page 32 and 33: 30 3.3 Nerves, muscles and behaviou
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Page 36 and 37: 34 4. THE LIFE OF PLANTS Cambridge
Page 38 and 39: 36 4.3 Reproduction Content Pollina
Page 40 and 41: 38 5. ENVIRONMENTAL STUDIES Cambrid
Page 42 and 43: 40 5.2 Measuring and conserving bio
Page 44 and 45: 42 Cambridge Pre-U Draft Section A
Page 46 and 47: 44 Assessment of skills in Componen
Page 48 and 49: 46 Cambridge Pre-U Draft Candidates
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Page 62 and 63: 60 Appendix 2: Textbooks and IT res
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Page 70 and 71: 68 Appendix 4: Performance Descript
Page 72 and 73: 70 Appendix 5: Additional informati
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