advertisement

Common Mistakes made in Chapter 1 – 6 #1 – Marginal distribution is always out of the TOTAL and only uses the #’s in the MARGINS not the body of the table. females males TOTALS cats 25 6 31 dogs 15 30 45 TOTALS 40 36 76 #2 – The mean is pulled in the direction of the skewness. This is skewed right so MEAN > MEDIAN #3 – Segmented Bar graphs must all be 100% tall. If the segments areas are EQUAL then the variables are independent. #4 – When discussing DISTRIBUTION talk about: SHAPE: Unimodal, Bimodal, Multimodal, Symmetric, Skewed Left, Skewed Right, Uniform CENTER: median, mean SPREAD: Range, IQR, Standard Deviation UNUSUAL CHARACTERISTICS: gaps, outliers #5 When data is skewed or has outliers use Median and IQR. When data is symmetric and unimodal use mean and standard deviation ( or range) #5 – Know how to find OUTLIER FENCES: Left Fence: Q1 – 1.5IQR Right Fence: Q3 + 1.5IQR #’s that fall outside the fences are considered outliers # 6 – Measures of Position: 5 # summary and Mean Measures of Spread: Adding/Subtracting(SHIFT) Multiplying/Dividing (RESCALING) Range, IQR, Standard Deviation Measures of Position CHANGE amount you + or CHANGE amount you • or / Measures of Spread DON”T CHANGE CHANGE amount you • or / Histograms are for QUANTITATIVE VARIABLES ( involve units) Bar Graphs are for CATEGORICAL VARIABLES ( group according to trait)