The American Association of Individual Investors (AAII) On-Line Discount Broker Survey polls members on their experiences with discount brokers. As part of the survey, members were asked to rate the quality of the speed of execution with their broker as well as provide an overall satisfaction rating for electronic trades. Possible responses (scores) were no opinion (0), unsatisfied (1), somewhat satisfied (2), satisfied (3), and very satisfied (4). For each broker summar scores were computed by calculating a weighted average of the scores provided by each respondent. A portion of the survey results follow (AAII website, February 7, 2012). Brokerage Speed Satisfaction Scottrade, Inc. 3.4 3.4 Charles Schwab 3.2 3.7 Fidelity Brokerage Services 2.5 2.6 TD Ameritrade 2.4 2.0 E*Trade Financial 2.4 2.2 Vanguard Brokerage Services 2.4 2.9 USAA Brokerage Services 2.9 3.2 Thinkorswim 3.4 3.4 Wells Fargo Investments 3.9 3.4 Interactive Brokers 3.9 3.8 Zecco.com 2.8 2.4 a. Select a scatter diagram for these data with the speed of execution as the independent variable.
Inverse Normal Distribution
The method used for finding the corresponding z-critical value in a normal distribution using the known probability is said to be an inverse normal distribution. The inverse normal distribution is a continuous probability distribution with a family of two parameters.
Mean, Median, Mode
It is a descriptive summary of a data set. It can be defined by using some of the measures. The central tendencies do not provide information regarding individual data from the dataset. However, they give a summary of the data set. The central tendency or measure of central tendency is a central or typical value for a probability distribution.
Z-Scores
A z-score is a unit of measurement used in statistics to describe the position of a raw score in terms of its distance from the mean, measured with reference to standard deviation from the mean. Z-scores are useful in statistics because they allow comparison between two scores that belong to different normal distributions.
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