ISB 208L Nature’s Numbers * Why Use Statistics? Statistics are sets of mathematical equations used to analyze what is happening in the world around us. Statistics also add confidence to the way we report our findings. Quiz Which of the following two graphs will have a greater standard deviation? Explain why. A B * Explain what a small standard error tells us about the averages (means) in comparison to all the values within that data set? Quiz * What Do Standard Errors Tell Us? Standard errors are calculations that show the accuracy of the population mean. Sometimes referred to as ‘Margin of Error’. Are these two data sets statistically similar or different? * Interpreting Standard Errors on Graphs Draw a horizontal line across the graph from each average’s error bar. If ranges overlap, then the differences in the averages are considered insignificant; that is, there is no statistically measurable difference between the two averages. If error bar ranges do not overlap, then the averages are considered significantly different, meaning there is sufficient data to suggest the values differ more than would be expected by chance alone. So what are we actually saying about the data. How would you communicate this to someone? * Graphs can be misleading! * Same Data with Errors Bars * Are these two data sets statistically similar or different? * * Today’s ObjectivesCollect Data & Create a Data TableCreate and Test a HypothesisCalculate & Plot Standard ErrorsAnalyze & Interpret Data Have fun with Madagascar Hissing Cockroaches! * Sexual Dimorphism (Males vs. Females) Sexual dimorphism is an observable difference between males and females of the same species. * Madagascar Hissing CockroachesThey live 2-3 years on average (sometimes up to 5!)They reach a size of 1.5 to 3 inches longThey are dark reddish brown to blackThey are hardy and docile and can easily be handled. Hissing cockroaches have a pair of modified spiracles (the tubes insects use for breathing) that they use to produce the hissing sound that inspired their name. * Testing a Hypothesis: I believe that only male hissing cockroaches hiss. Do not be afraid to handle the specimens, but they are living creatures so handle them carefully. Is this hypothesis Supported or Refuted? Males have more pronounced ‘horns’ * Create a Sexual Dimorphism Hypothesis: Look at the last abdominal segment on the ventral side of both male and female cockroach at your table and create a hypothesis as to which has the longer abdominal segment. Decide as a group whether males or females will have a longer last abdominal segment on average – record your hypothesis on the worksheet. * We are going to measure sexual dimorphism based on the length of the last abdominal segment. 1. Measure (in millimeters) the length of the last abdominal segment on the ventral side of both male & female. 2. Repeat on ...