Transcript File
Statistics Day First: • Turn in your Mung Bean Lab • Turn in signed form (safety contract can wait till tomorrow) • Phones: Remind(101): enter 81010 and text @apdcbiolo • Computer: check out Beachbioeyw.com • Go to your class. • Go to Ecology tab (at bottom of “chapters”) • Password LifeRocks! • A “fix” on the first set of objectives is the big hand-out you picked up • Some Q’s were omitted, some added – if you’ve started on the previous one that’s OK, just check off which Q’s you’ve done on this one and continue on… • More Stats Worksheet (the other handout) – Standard Deviation added – notes begin next slide Standard Deviation • In statistics, the standard deviation (SD, also represented by the Greek letter sigma, σ for the population standard deviation or s for the sample standard deviation) is a measure that is used to quantify the amount of variation or dispersion of a set of data values The formula is easy: it is the square root of the Variance. • Variance = The average of the squared differences from the Mean. Example: You and your friends have just measured the heights of your dogs (in millimeters): The heights (at the shoulders) are: 600mm, 470mm, 170mm, 430mm and 300mm. The mean = 394 Now we calculate each dog's difference from the Mean: To calculate the Variance, take each difference, square it, and then average the result: To calculate the Variance, take each difference, square it, and then average the result: So, the Variance is 21,704. • The Standard Deviation is just the square root of Variance, so: • Standard Deviation: σ = √21,704 = 147.32... = 147 (to the nearest mm) Population (our example) vs Sample • When you have "N" data values that are: • The Population: divide by N when calculating Variance (like we did) • A Sample: divide by N-1 when calculating Variance Population Sample