Statistics

• Averages with Examples [Eric, 10/17/2001]
  My teacher has explained three ways to figure out averages, kind of like weighted avererages, but without the weight...

• Finding Outliers [Stu, 09/11/2001]
  How can you use the range of a set of numbers to determine whether any of the observations were outliers?

• Grade and Test Averages [Adam, 12/02/2001]
  In a class of 21 students the average score on a math test was 77%. If Suzie got 95% and Jack got 78%, find the average grade of the other 19 students.

• Measures of Dispersion [Ivan, 6/30/1996]
  What are the different characteristics of: Range, Mean Absolute Deviation, Standard Deviation, Variance, Quantiles (percentile, decile, quartiles), covariance?

• Questions About Standard Deviation [Morris, 9/20/1995]
  Why does a standard deviation take the square root of the average of the sum of the squared differences between X and X mean instead of the average of the absolute value differences? What is the reasoning behind dividing by n vs. n-1 in the population versus sample standard deviations?

• Sample and Population Standard Deviation [Brook, 03/03/2001]
  What letters represent theoretical and 'real' standard deviation, mean, and variance?

• Weighted Averages [Smith, 11/02/1998]
  Can you explain the concept of weighted averages, with examples?

• Regional Marathon Problem [Yoshida, 1/9/1995]
  Those wanting to participate in a state marathon race must first qualify by running in a regional marathon...If there are to be only 600 runners in the state marathon, what is the slowest time that will qualify a regional runner for the state race?

• Median and Middle [Haldar, 5/15/1996]
  I would like to know how to find the median of two of the same numbers (2 and 2).

• Statistics: Graphs and Pictograms [Fry, 6/6/1996]
  In statistics, what makes a graph a pictogram?

• What Field Studies Small Groups with a Characteristic? [Boston, 6/10/1996]
  What field studies questions like: 1. Take for example that person A has blonde hair. 2. You know that this person is not famous. 3. You also know that (10) people know person A. 4. You would like to know that if (10) people know person A, how many people in a given population also know someone like person A, someone with blonde hair. 5. You really want to know how many people with blonde hair there are in a given population given the answer to #4.

• Proof of Bernoulli's Law [Peter, 6/22/1996]
  I would like to know how one can prove Bernoulli's law of large numbers

• Normal Distribution [SimonFlack, 6/24/1996]
  In six successive independent 'triple jumps' what is the probability that at least one total distance will exceed 18 meters?

• IQ Tests and Standard Deviation [Sets, 7/28/1996]
  On standard IQ tests, the mean is 100, with a standard deviation of 15. Find the percent of people whose IQ scores are greater than 115...

• IQ Scores by Category [Spruill, 7/28/1996]
  Suppose an IQ test is given to a large group of people. Find the percent of people whose IQ scores fall into the following categories...

• Finding the Standard Deviation [Timm, 8/5/1996]
  What is the formula for calculating the standard deviation?

• Binomial Distribution [Chuin, 8/25/1996]
  The mean life of a certain television tube is 1200 hours with a standard deviation of 200 hours... The probability that three machines will be in use on any one day is 0.8,0.7 and 0.6 respectively.

• Winning the Lottery [Zink, 01/30/1997]
  Can you find a formula that predicts the outcome of the lottery?

• Weighted Coin Project [Spivak, 02/01/1997]
  Analyze the results from flipping a non-weighted coin and a weighted coin.

• Covariance [Rizzo, 02/05/1997]
  What does covariance represent?

• Best Line Fit: Least Squares [Litrownik, 03/23/1997]
  What is least squares fitting? How exactly does one do it?

• 20 Golf Players [Mullen, 04/11/1997]
  How do you set up four teams such that the variance in the average team handicap is no more than one or two?

• The First Ace [Klinow, 06/12/1997]
  An ordinary bridge deck of 52 cards is thoroughly shuffled. The cards are then dealt face up, one at a time, until an ace appears. What is the probability that the first ace appears at the kth card or sooner?

• Standard Deviation [Bowell, 07/05/1997]
  Given the average height of a group of students and the standard deviation, find the percentage of students who are taller or shorter than the average.

• Null Hypothesis, Deviation [Amanda, 08/05/1997]
  A statistician believes that on the average the members of a group of people weigh 120 pounds...

• Sample Variance [Murray, 08/08/1997]
  Could you help me understand the sample variance using the data 4,5,2,6,4,3,4 where n = 7 and X = 3.52?

• Student Grades [Hunter, 08/13/1997]
  The grades of the students are normally distributed with a mean of 74 and a standard deviation of 10...

• Ordering Probabilities [Hunter, 08/13/1997]
  The proportion of people who order coffee with their dinner is .9. A simple random sample of 144 patrons of a restaurant is taken...

• More Living or Dead? [Zifkin, 08/14/1997]
  Are there more people living now than have ever died?

• Spearman Rank Correlation Coefficient [Binek, 08/26/1997]
  I would like to get a clear definition of Spearman's Rank and how it is used.

• Scaling Test Scores [Hung Lo, 09/28/1997]
  How do professors and teachers use standard deviation to scale scores?

• Proof of Normal Distribution [Sauter, 10/15/1997]
  Can you explain (and prove) why samples taken from a normally distributed population will also be normally distributed?

• Regression Method [Navarro, 11/18/1997]
  What is the regression method?

• Percentage Less than a Given Value [Green, 11/22/1997]
  If some data are normally distributed, and I know the mean and the standard deviation, how do I find out what percentage of the sample is less than (or greater than) a given value?

• Interquartile Range and Standard Deviation [Dave, 11/24/1997]
  What are some uses of interquartile range and standard deviation?

• Pi and Probability [Leduc, 12/21/1997]
  I'm doing a report for my math class on the relation between pi and probability...

• Large Standard Deviations [Peet, 12/24/1997]
  Is there a way to calculate the percent values derived from the z-table without using the table, i.e. a formula?

• Counting Techniques [Kate, 12/29/1997]
  Find the number of positive divisors of 17640, inclusive of 1 and 17640 itself. Find the number of odd integers between 2000 and 7000 that do not have repeated digits.

• Standard Deviation of Sample [Amerlan, 01/12/1998]
  How can a given sample population have a narrower variance, hence a narrower standard deviation, than the entire population?

• What is a Median? [Sean, 03/03/1998]
  A definition of median, and four examples of calculating medians.

• Calculating and Interpreting Expected and Chi-Square Tables [Kelly, 04/10/1998]
  How do you calculate the expected frequency and chi-square value of a 3-by-3 table?

• Several Probability and Statistics Techniques [Evans, 04/13/1998]
  Examples of binomial distribution, Poisson distribution, significance test, and calculation of confidence interval.

• Interpreting Stemplots [Danilou, 05/11/1998]
  What does a stemplot represent, and how does it relate to the overall population?

• Testing the Difference of Two Averages [Delight, 05/27/1998]
  I am given two averages, and I need to test whether they are statistically different.

• Grocery Store Statistics [Delight, 06/10/1998]
  Can you help me find confidence intervals and test for statistical difference on grocery store service time data?

• Standard Deviation and Conditional Probability [Williams, 07/14/1998]
  If a sample has one element, what is its standard deviation? Also, can you help me with a conditional probability problem?

• Benford's Law [Edwards, 08/06/1998]
  What is Benford's law?

• Representing the Average [Cleatus, 08/18/1998]
  Suppose a, b, and c represent one student's scores on three math tests. Write an expression for the students' average if: a) all three tests count equally; b) the last counts as if it were two.

• The Correlation Coefficient [Krompf, 09/11/1998]
  How do you determine the correlation coefficient of a set of data, and its significance?

• One Tailed, Two Tailed t-Tests [Newman, 09/11/1998]
  What is the difference between a one-tailed and two-tailed t test?

• Understanding Standard Deviation [Basehore, 09/14/1998]
  If two samples have different standard deviations, will the sample with the larger or smaller standard deviation show more variability?

• Graphing Scatter Plots [Alice, 09/26/1998]
  How do I make a scatter plot for height and shoe size? How can I make a graph online?

• Interpolation Polynomials and Linear Regression [Cathala, 10/09/1998]
  I need to find the polynomial of a temperature curve using some data I have gathered.

• Random and Pseudorandom Numbers [Sagebiel, 10/13/1998]
  When are the numbers of a sequence truly random numbers and not pseudorandom?

• Stem and Leaf and Scatter Plots [Curre, 10/13/1998]
  I'm looking for information on stem and leaf plots and scatter plots.

• Yahtzee Probabilities and a State Matrix [Ryan, 12/30/1998]
  In Yahtzee, what are the odds of rolling 5 of a kind within 3 rolls of the dice? What if you reroll all 5 dice each time? Does this involve transition matrices?

• Correlation of a Scatterplot [Rebecca, 02/04/1999]
  Draw a scatterplot that represents no correlation, no positive correlation, and no negative correlation.

• Rating Ski Slopes [Chris, 02/07/1999]
  Can you help me rate the best ski slope value, based on data that I've collected?

• The Power of a Statistical Test [Kohut, 02/11/1999]
  How do you find the power of a test, given the significance level?

• Spearman's Rank Correlation [Bobby, 02/17/1999]
  Where does the 6 in the formula of Spearman's rank correlation come from?

• Calculating Percentage Errors [Brandy, 02/20/1999]
  How do you calculate percent error from a set of data that includes predicted values and observed values?

• Mean and Standard Deviation [Maria, 03/01/1999]
  Prove that the mean (u) and standard deviation (s) for a binomial distribution are np and the square root of (npq).

• Randbin [Robert, 03/14/1999]
  Consider an airplane that has 113 seats... what is the probability that at most 113 will check in?

• Lifespan Probability [Dye, 03/26/1999]
  The probability that a general population will live past 85 is estimated to be 5.4 percent...

• How Many Samples? [Carboni, 03/30/1999]
  For a continuous operation, how does one determine the necessary number of samples so that the mean of the samples represents the mean of the whole?

• Standard Normal Random Variable [lowe, 04/19/1999]
  Find each of the following for a standard normal random variable Z...

• Hypothesis Testing [Long, 04/22/1999]
  Why when the p-value is lower does the null hypothesis value fall more easily in the 95% confidence interval?

• Batting Averages [Caleb, 05/07/1999]
  How do you calculate batting averages? Do you have to average the new hit into all the previous hits?

• Significant Difference? [Rita, 05/08/1999]
  A research question: does mean delivery time differ for boy babies and girl babies?

• Standard Deviation [Rob, 05/17/1999]
  What is standard deviation?

• Binomial and Normal Distribution [Emma, 06/09/1999]
  Could you please tell me the difference between normal approximation to binomial distibution and normal distribution?

• New Pension Plan [Mcgraw, 07/15/1999]
  Is there an relation between age and an employee's opinion of the new plan?

• What is the Regression Line? [Alison, 08/09/1999]
  Determining the line that is as close as possible to passing through all the points on a scatterplot.

• Expectation and Hypothesis Testing [Wright, 08/24/1999]
  Four problems related to expectation and hypothesis testing in statistics.

• Statistics of Grouped Data [McCabe, 09/12/1999]
  Can you show me how to find the mean, standard deviation, variance, and median class of grouped data?

• Arrangements of Letters [Kevin, 09/14/1999]
  In how many ways can the letters in UNUNSUAL be arranged? For those arrangements, how many have all 3 U's together?

• Quartiles and Interquartile Range [Newton, 10/27/1999]
  What is interquartile range? How do you calculate Q1, Q2, and Q3?

• Averaging Averages [Francis, 11/09/1999]
  How can I average the results of a survey sent to 5 different departments if I only have averages from each department?

• Finding a Formula That Fits the Data [Mullen, 01/26/2000]
  How can I find a formula that fits a chart of tensile strength data I've collected?

• Box and Whisker Plots [Martinez, 02/13/2000]
  Can you explain how to make and use box and whisker plots?

• Analyzing Survey Results [Davis, 05/04/2000]
  How can I determine a ranking of priority (1st, 2nd, 3rd, etc.) for the results of a satisfaction survey that asked people to rank, in order of importance, seven factors?

• Box and Whisker Plots [Ashley, 05/18/2000]
  If there is an odd number of points in a data set, is the median considered to be part of the subgroup used to find the upper (or lower) quartile?

• Chi-Squared Test for Independence [Leanna, 05/24/2000]
  A hospital commissioned a study to see if there was a difference between the quality of care provided by hospital-trained and tertiary- trained nurses. How can I tell if the two events are independent?

• Poisson as a Limit to a Binomial Distribution [Sykes, 05/29/2000]
  How do I prove that the limit of a binomial distribution with large n and small p is a Poisson distribution?

• Mode of a Uniform Distribution [Kennedy, 09/06/2000]
  What is the mode of a set of numbers, if none of the numbers repeat themselves? What about a set like {1,1,2,2,3,3}?

• Finding Outliers [Caitlin, 09/28/2000]
  How is the 1.5*IQR criterion used to find outliers in statistics?

• Standard Deviation of Grouped Data [Laura, 10/16/2000]
  How do I find the standard deviation of grouped data in a frequency table? Also, how many significant digits should the mean of a data set have?

• Local Modes and Bimodal Distributions [Laura, 10/22/2000]
  What does it mean if a frequency distribution shows two peaks?

• Runs Batted In and Earned Run Average [Tara, 10/26/2000]
  How do you calculate RBI for a player on a baseball team? Also, how do you find a pitcher's ERA?

• Outliers in a Box-And-Whisker Plot [Tucek, 12/07/2000]
  Would a point that is exactly 1.5 times the IQR away from the inner or outer quartiles be considered an outlier?

• Standard Deviation for Variance? [Lobmayer, 01/25/2001]
  I would like to calculate a measure of the reliability of my data. The best would be the standard deviation of variance. Does such measure exist?

• Ice Skating Scoring [Johnny, 01/27/2001]
  Why does the U.S. Figure Skating Championship use only five scores out of the seven given by judges?

• Stock Market Scam [Gray, 02/08/2001]
  Every Monday a firm sends you a letter correctly predicting the behavior of a given stock over the coming week. In the 8th letter the firm offers to sell you more predictions for a fee. You refuse. Why?

• The Law of Large Numbers [Rothstein, 02/08/2001]
  Can you give me a brief explanation of the law of large numbers?

• Find the Mode of a List [Gon, 02/26/2001]
  Is it possible to use other statistical measures to find the mode of a list of numbers, without knowing the numbers themselves?

• Outliers [Ben, 03/14/2001]
  What is the definition of an outlier?

• Which is the Best Description? [Notesetine, 03/25/2001]
  Which best describes the number of times "Popular Song" was played on the radio per day: the range, the median, the mode, or the mean?

• Examples of Weighted Averages [Thomas, 03/26/2001]
  Can you tell me what is meant by "weighted average," and give me some examples of when and how weighted averages are used?

• Arithmetic vs. Geometric Mean [Mark, 03/27/2001]
  When is it appropriate to use the arithmetic mean, and when the geometric mean?

• Mean, Average, and Standard Deviation [Matthew, 04/18/2001]
  Why is the average of means of three groups not always equal to the mean of the three groups put together?

• Rolling a Die 600 and 5000 Times [Tory, 06/03/2001]
  Toss a die 600 times, 5000 times. How many times does each number come up? Approximately how many would you expect?

• Bayesians and Frequentists [Ellen, 08/21/2001]
  What is the difference between Bayesian and "regular" statistics?

• Statistical Bias [Kendra, 09/27/2001]
  Suppose that insted of choosing random samples of 25 students from a population of 100 students, you selected the first 25 students for the first sample, the next 25 students for the second sample, and so on. How might this sampling procedure bias the statistical results?

• Distribution of Chi-square and F [Mike, 12/03/2001]
  Do chi-square and F have a mathematical relation?

• What Does AVERAGE Mean? [John, 12/05/2001]
  Can someone explain what average is? For example what is the average rainfall in New York? I understand the formula needed to find the average, but what is the meaning of average?

• Averaging Kelly's Test Scores [Brittney, 01/07/2002]
  Kelly's average score on 4 tests is 85.5. The average of her 3 highest scores is 87, and her two lowest scores are the same as each other. What is the average of her two highest test scores?

• Ratioing Errors [Rich, 01/07/2002]
  How do you calculate the error bars for ratios?

• Manipulated and Responding Variables [Katie, 01/13/2002]
  What are manipulated variables and responding variables?

• Statistics - t-test [Pierre, 01/15/2002]
  I am comparing scores of basketball games to see if playing at home is an advantage over playing away.

• Mode, Mean, and Median in Stemplots [Linda, 02/21/2002]
  How do I find a mode, mean, and median, using a stem/leaf plot?

• Significance of Handwashing Frequency [Adam, 02/23/2002]
  I need to determine whether the absence of an observer makes a statistically significant difference. I think I need to use a chi- squared test...

• Simpson's Paradox [Emily, 02/27/2002]
  What exactly is Simpson's Paradox (a.k.a. Stein's Paradox)?

• Random and Systematic Errors [Richard, 03/05/2002]
  What are 'random errors' and 'systematic errors'?

• Central Limit Theorem [Stephanie, 03/08/2002]
  The probability that a drug is effective in any one patient is 62%. Find the probability that, of the next 200 patients, at least half (or more) will survive.

• Finding a Mean in a Survey [Lisa, 03/13/2002]
  Question submitted via WWW:I have to figure out how to get a mean from a group of numbers after extracting a certain group of survey respondents...

• Population Densities [Hannah, 03/17/2002]
  Given population data, how many people would have to move from Connecticut to Wyoming to make the population densities the same?

• Re-Calculating the Standard Deviation [Gareth, 03/20/2002]
  How can I re-calculate the standard deviation of a set of values when I insert a new value but I don't know what the existing values are?

• Calculating Percentage of Errors [Rod, 03/21/2002]
  You have items to be picked off a shelf every day. You pick one item a day and check it against the order. You wish to asign a percentage to the error in wrong items and/or number of items.