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lec7_jls - BE.104 Spring Biostatistics: Distribution and...

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BE.104 Spring Biostatistics: Distribution and the Mean J. L. Sherley Outline: 1) Review of Variation & Error 2) Binomial Distributions 3) The Normal Distribution 4) Defining the Mean of a population Goals: 1) Understand the concepts that underlie common statistical analyses for EHS studies 2) Evaluate them! Appropriate use? Quality? Meaning? 3) Requires familiarity with operations & mathematics; but not formal training to be a statitician Why do we need statistics in EHS? 1) To organize data for analysis 2) To quantify error 3) To quantify and compare variation 4) To detect differences between populations e.g. affected vs non-affected exposed vs non-exposed 5) To detect relationships 6) To make predictions about events in the future; specifically to estimate risk The Basic Tool for Organization of Population Data: Frequency Plot or Distribution Value of measurement # of occurrences a i b i i c iii d i v e v f v i g v i i Population People Towns “measurements” sample # value
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1) All measurements and observations are samplings (e.g., heart rates, bead numbers, hand measurements) There is an ideal universe of all our measurements that is infinite. We are tying to estimate the characteristic features of this ideal universe of measures. Why? To develop the Best representation of reality. The Best representation of risk, prediction, difference. If we measured body weight, how would the plot look? We expect variability in this measure… its expected variation… remember this type of variance is always present (biological, quantitative, statistical) Now, suppose I gave each of you a ruler (12 inches) and asked you to measure this table. How would the distribution of measurements look? <Graphs> What if I gave you 100 1-foot rulers and asked you to measure them with a 2-ft. ruler? <graph> We called the spread in data variance (mathematical definition later.) Three sources of variance in population distributions: Variance } I) Errors of measurement (quantitative, investigator, seasonal) II) Variation (statistical, sampling, biological, physical) III) "Things are really different. More than one distribution present."
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I)
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lec7_jls - BE.104 Spring Biostatistics: Distribution and...

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