Statistical Tests Using Minitab

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What Statistic Should I Use? Statistical Tests Using Minitab Stats Menu When designing an experiment you should have an idea of how you will analyze the data after it is collected. This way you will not conduct the experiment and then find out you did not collect data in an appropriate way to analyze it. Although not considered statistical tests, the following procedures will be helpful as you begin the analysis of patterns in a data set. Calculating descriptive statistics Making an interval plot Determining the 95% confidence interval Often an experiment is designed to determine the difference caused by an experimental variable. For most of the experiments you will be doing we will assume the data form a normal distribution (bell-shaped curve) and parametric statistics can be used. If the data are not normally distributed you will need to consult with your instructor and use one of the slightly less sensitive, non-parametric statistical tests. A summary of the major tests used in Biology 109 is given below. By clicking on a test name you will be linked to information on when to apply it, how to organize the data in Minitab, and how to interpret the test results. Use back to return to this chart. Stat ->Basic Statistics -> Display Descriptive Statistics -> Variable (select all the columns you want to have the statistics calculated for ). Using a Code Column to Calculate Descriptive Statistics: use this to divide the data in a single column into several treatments based on the codes in the code column. Stat -> Basic Statistics -> Display Descriptive Statistics -> Variable LDC (data column) -> By Variable (after selecting this option) -> LDC (code column) The following information will be displayed in the session window : N = the # of individuals in the sample (the total # of students in the sample). MEAN = the average (e.g. . the average resting pulse rate if you specified C1). MEDIAN = the middle value; 50% of values (e.g. . pulse rates) are above, 50% below the median. If N is an odd #, then the median is, in fact, the middle value; if N is an even #, then the median is half way between the two middle values. TRMEAN = the 5% trimmed mean. First the data are sorted - lowest to highest. Then the lowest 5% and the highest 5% of the values are discarded; the remaining 90% are averaged to give the trimmed mean. Use of the trimmed mean allows one to discard the most extreme values that may fall well outside of the range of the majority of values in the sample. ******Calculating descriptive statistics: use this to summarize data and get a sense of variability. Page 1 of 6 statistics 2009-08-04 http://biology.kenyon.edu/courses/biol09/stats.htm

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STDEV = the standard deviation, the average deviation of the individual measurements from the mean - a measure of how spread out the data are. Recall that for a normal distribution 68% of the data values fall between one standard deviation above and one standard deviation below the mean. SEMEAN
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## This note was uploaded on 04/07/2012 for the course IBE 340 taught by Professor Valerieozaki during the Spring '09 term at Sophia University.

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