Week 2 Outline

• Review frequency bar chart for showing distributions in Excel

Here's a guide to using Excel to create bar graphs including a frequency bar graph (histogram). Here's a link that uses the Analysis Toolpak.

• Review describing distributions with numbers (Section 1.2)
• Min and max
• Mean (x-bar)
• Median (M)
• Mode (value with the most data elements)
• Quartiles and Percentiles

The 5 number summary of min, max, mean and 1st and third quartile is often shown with a box-plot.

• Measuring spread of quantitative data
• Difference between min and max
• Interquartile range (IQR --- 1.5 * IQR is used to throw out outliers)
• Average difference from the mean
• Variance (s²)-- average squared difference from the mean
• Standard deviation (s)-- square root of the variance

Note that different texts use different formulas for calculating the varience and consequently the standard deviation. In its simplest form, the variance is just an average. That is, the sum of the squares divided by n (the number of data elements). This is sometimes called the population variance. However, our text divides by n - 1. This is sometimes called the estimated variance based on a sample. By some measures, it provides a more accurate estimate of a whole population.

• Review first assignment
• Normal distributions
• Using z-scores for probability predictions

We'll work out a few examples in class.

• Discuss assignment 2
• Data files for discussion
• Service call lengths (from M&M text 5th edition Table 1.1)
• Web Navigation times when given a scenario
• Data collected from class survey
• Historical NASDAQ performance