# Recent content by mathprof

1. ### Which test for significance?

I have 2 classes. Class #1 takes a pretest and then a posttest on a topic. Class #2, on the same topic, also takes a pretest and a posttest. However Class #2 also watches videos about the topic. I want to test whether there is a significant difference between the two classes of students as it...
2. ### Normal Curve Outliers

Thanks hlsmith. So you are saying that there is no consensus. I understand. Seems to me most choose z>2 (or z<-2) Possibly because of the choice of popular 95% for confidence intervals. I'm curious whether the 1.5*IQR decision for outliers would confirm 2 or 3. Thanks for your response.
3. ### Normal Curve Outliers

Are outliers more than two or three standard deviations from the mean?
4. ### How many standard deviations to determine outliers

Are outliers more than two or three standard deviations from the mean?
5. ### Scatterplot Outliers

Looking for Visual Basic Code to detect outliers in a scatter plot. I suspect that I need to calculate the distances of each point to the regression line. If so, then what? What would the formula involved look like. Thanks.
6. ### Looking For Statistics Tutorial Software Reviewers

No, not videos. Easy to navigate Tutorial software that will work off a USB. 15 minute learning curve. Random problems with always different numbers, step by step solutions. All Topics covered in Intro Stat courses. Descriptive Statistics, Graphs, Correlation, Normal Curve, Central Limit...
7. ### Looking For Statistics Tutorial Software Reviewers

Are you teaching an Introductory Statistics Course. ? I am, at Essex County College in Newark NJ. I have been developing tutorial for this course and need critical reviews from similar faculty. Can you help? Moderator: I am not selling. I just need to know if I am on the right track. If this...
8. ### Why One Sample For Confidence Intervals?

One of many descriptions of the CLT follow: "The Central Limit Theorem (CLT for short) basically says that for (even) non-normal data, the distribution of the sample means has an approximate normal distribution, no matter what the distribution of the original data looks like, as long as the...
9. ### Why One Sample For Confidence Intervals?

As I understand it, The Central Limit Theorem and Confidence Intervals are related. What is the best way to explain why the Confidence Interval formula uses only one sample whereas the Central Limit Theorem uses 'many' samples? Isn't the x-bar in the CI formula the mean of one sample? Don't we...
10. ### App To Find Chi Square sample size

I'm looking for a simple app for my students to use when they are doing a project involving Chi Square and need to estimate the sample size. What's available?
11. ### Is the Null Hypothesis ... ?

If the alternative hypothesis is mu>13 then what is the null? Is it a) mu<=13 or b) mu=13 I've seen both a) & b) so what's the rationale for each one?
12. ### Any Suggestions A Good Discussion Topic For An Online Intro Statistics Course

I'm teaching an online Intro Statistics Course for the first time. This week my Discussion Forum Topic is "How will Statistics be important in the your career choice?" Students are supposed to reply to my Question then they must reply to the responses of two other students. I'm looking...
13. ### need formula can youn help?

find minimum sample size P(s2/sigma2 <1.75) >.95
14. ### observed z ratio

When null hypothesis is population mean 1 = population mean 2 given population s variances and sample sizes and sample means I calculate the SE (standard error=3.51) and DF (degrees of freedom)=40.47 giving me a t=-1.99. Now, p(t<-1.99)=.027 and p(t>1.99)=.027 so my p-value= 0.054. Need...
15. ### Conditional Probability?

What is the probability on a single roll of a pair of dice, that the sum is 6, given that at least one die came up 1? I'm thinking that there are 11 ways to roll the pair with a 1 on at least one die. Of those 11 ways 2 sum to 6 (1&5, 5&1), so my answer is 2/11 Is this correct?