I'm also confused.  When B says to compute the test statistic for the Null Hypothesis, do we use the formula for t0 given on the bottom of page 104?  Or do we lookup the t-value using the degrees of freedom and the alpha / 2?  What is the t-value we want to be using for the confidence interval in C?  Is it -2.6 or is it 3.18?

For part C, is anyone getting CI = -0.9 +/- 3.1825(0.3464)= -0.9 +/- 1.1025 ?

The +/- 1.1025 seems awfully wide to me. Are my units messed up when calculating SE(B)?

Thanks for the help!

I am getting -2.59808 for Part B. Does a negative t statistic make sense? Because of a negative t statistics I cannot find a p-value for it.

[NEAS: p-value is the same for a negative t as a positive t.]

I got the same answer... it matched the result in Excel. I'm still working on the p-value.

I am getting -2.59808 for Part B. Does a negative t statistic make sense? Because of a negative t statistics I cannot find a p-value for it.

[NEAS: t statisics are positive or negative, depending if the estimated parameter is positive or negatiave. Use the absolute value of the t statistic for the p-value.]

Is there anyway to get the p value in part D by hand?  (without using Excel)

I don't see any examples of this in the book or notes so far.

[NEAS: The p value is the CDF of a standard normal distribution. Before the advent of microcomputers with Excel, statisticians used CDF tables. Textbooks on statistics had the CDF table in the back, and students learned to look up values. The CDF of a normal distribution has no closed form solution, so one can't work out the p-value by pencil and paper.]

I am getting -1.5 (or-150%) for part B and 205.26% for part F...does this make sense?

I got SE(B) is .6 and SE(A) is 15.69%...is that correct?

For the p-value, I use TDIST(x, degrees_of_freedom, tails). x = t statistic; degrees_of_freedom = n - 2; and tails = 1 for strictly > or strictly < tests and 2 for either < or < tests.

wangxy, from module 8, I got SE^2 = .00012 = .012%.

In Excel, I think we want TINV(probability, degrees_of_freedom). Probability = a and degrees_of_freedom = n - 2. I was able to get the t-value in the example on page 105.

Which excel function do I use to get the P value from T value?

I got V(B) = 198, S^2 = 0.0198( from Module 8 assignment), sum of (Xi-X bar)^2 = 0.02*5. Is it correct? 198 seems too high. My B from module 8 equals -0.9, therefore I got my T0= 0.06396.

For homework items D and H, how are we suppose to calculate the p values? Is there a table? In the textbook, the readings for this section don't have a formula or even talk about p values. Also, is there a t table somewhere? How do I get the t value for the confidence interval? Also, how does the hypothesis testing work?

[NEAS: The p-value is the flip side of the critical t-value. If the critical t-value for a significance level of 5% is 1.96, then the p-value for a t-value of 1.96 is 5%. Years ago, we used tables; now we get the significance from Excel of other software. Read the discussion of Type 1 errors, Type 2 errors, and the null hypothesis. Classical regression analysis tests whether a null hypothesis should be rejected at a given significance level. We can never say that a specific hypothesis should be accepted. There is always a range of hypotheses that can not be rejected.

Several student comments below discuss getting t values and p values from Excel. Questions on final exam issues also have responses from NEAS. Excel, R, SAS, and other statistical software have many ways of getting t values and p values. Feel free to comment on the statistical software in this discussion thread.]