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Review Cards

# Review Cards - Difference Subject 1 151 125 26 Subject 2...

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Bad Adjustment Total Orientation 72 14 86 No Orientation 28 45 73 Total 100 59 159 Difference Subject 1 151 125 26 Subject 2 167 136 31 Subject 3 137 120 17 Average 151.6667 127 24.6667 # ( obs . " exp . ) # Important Terms • Population – Total set of subjects in which we are interested • Sample – A subset of the population for which we have data • Subject – Entities we measure (individuals) Histogram Interpretation How many total students sampled? Which class has highest / lowest frequency? What are those frequencies? How many students have an IQ between 110 and 129? Stem-And-Leaf Plot • A bar chart on its side • “Stem” is all digits except the last one • Last digit is the “leaf” • Ascending order • No commas • If nothing in a row, write the row, but leave it blank Example (HW 2.1-2 2) eBay selling prices 199 210 210 223 225 225 225 228 232 235 Sampling Methods • Simple Random Sampling – Each subject everywhere has an equally likely chance of being selected – Often done with a random number table – Choosing a company somewhere in the U.S. • Systematic – Selecting every “ k -th” subject – Surveying every 10 th person we meet downtown • Convenience – Individuals are easily found (e.g. internet surveys) – Often the “laziest” way, so less reliable answers

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Sampling Methods Skewness Stratified  Sampling Taking  some subjects from  all possible groups Cluster Sampling Taking  all subjects from some possible groups
Outliers • The mean is sensitive to outliers. • The median is resistant to outliers. • When outliers are present, best to use median as measure of central tendency. • Example: average selling price of homes in the U.S. Standard Deviation • The average distance between any data point and the mean of the data. • Measures how much/little the data distribution is spread out. Summ ary Stats Interpr etation Mean – Average of the data set Median (also called Q2) – About 50% of data lie below (and above) his value. Range – Difference between maximum and minimum Max & Min – Highest and lowest points in data set Q1 and Q3 – 25% and 75% percentiles Interquartile Range (IQR) – Difference between Q3 and Q1 B o x - P l o t ( H W 2 . 5 - 2 . 6 ) D i s t r i b u t i

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o n o f t a x e s ( i n c e n t s ) Minimum = 2.6 Q3 = 105 Q1 = 31 Maximum = 206 Median = 55 Construct a box-plot for this data. What proportion of states have taxes… – Greater than 31 cents? – Greater than \$1 05 (105 cents) ? Find the range and the interquartile range (IQR). Box-Plot Outlier Test (HW 2.5-2.6) Any point lying above Q3 + 1.5 x IQR is an outlier. Any point lying below Q1 – 1.5 x IQR is also an outlier. Are there any outliers on this box- plot? Mean & Median (HW 2.3- 2.4) This chart shows the number of grams of protein in various brands of loafs of bread.
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