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Statistics for IB Biology Syllabus Topic 1

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1.1.1: Error Bars State that error bars are graphical representations of the variability of dataState that error bars are graphical representations of the variability of data –Graph Pad tutorial Graph Pad tutorialGraph Pad tutorial –Excel instructions Excel instructionsExcel instructions

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Interpreting Statistics is as important as collecting the data http://davidmlane.com/ben/cartoons.html

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1.1.2: Mean and Standard Deviation Calculate the mean and SD of a set of valuesCalculate the mean and SD of a set of values –Mean or μ or x bar = x n –Standard Deviation or S –For this course we will use the sample std. dev., NOT the population std. dev.

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1.1.3: Spread of Values The term standard deviation is used to summarize the spread of values around the mean.The term standard deviation is used to summarize the spread of values around the mean. Sixty-eight percent (68%) of the values fall within one standard deviation of the mean.Sixty-eight percent (68%) of the values fall within one standard deviation of the mean. –1 st SD contains 34% of the data points on each side of mean (34+34=68) –2 nd SD contains 13.5% of the data points on each side of the mean –3 rd SD contains the remaining 2.5% of the data of each side of the mean

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Standard Deviation SD=1 Graphs from: http://www.childrensmercy.org/stats/definitions/stdev.htm SD=2 SD=3

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1.1.4:Comparing Means Explain how the standard deviation is useful for comparing the means and the spread of data between two or more samplesExplain how the standard deviation is useful for comparing the means and the spread of data between two or more samples –What can you conclude when standard error bars do overlap? No surprises here. When SE bars overlap, you can be sure the difference between the two means is not statistically significant. –What can you conclude when standard error bars do not overlap? When standard error (SE) bars do not overlap, you cannot be sure that the difference between two means is statistically significant. T-test is commonly used to compare these groups. –What if you are comparing more than two groups? If two SE error bars overlap, you can be sure that a post test comparing those two groups will find no statistical significance. However if two SE error bars do not overlap, you can't tell whether a post test will, or will not, find a statistically significant difference. ANOVA is commonly used for comparing multiple groups. from - http://www.graphpad.com/articles/errorbars.htm

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Data Never Lies, it just needs the proper explanation http://davidmlane.com/ben/cartoons.html

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1.1.5: T-tests Deduce the significance of the difference between two sets of data using calculated values for t and the appropriate tables.Deduce the significance of the difference between two sets of data using calculated values for t and the appropriate tables. –used for comparing two groups of data (ANOVA for 3 or more) –GraphPad tutorial GraphPad tutorialGraphPad tutorial

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