Can someone please help me with the Student's T Test?? How do i decide whether i want a 1-tail or 2-tail?

Question

I am pathetic with statistics... for instance, i am trying to work out whether the data that i have obtained for one modified experimental model is greater than another without the modification (i.e. the control model). so do i need a 1-tailed test or 2-tailed test? and what about if the t value is greater than the number in the table (according to degrees of freedom) - does that mean that i reject the null hypothesis (which is that the means are the same)? help!!!!! i'm going nuts!

Answer 1

One Tailed Test: When your research hypothesis states the direction of the difference or relationship, then you use a one-tailed probability.
For example, a one-tailed test would be used to test these null hypotheses: Females will not score significantly higher than males on an IQ test. The null hypothesis (indirectly) predicts the direction of the difference.

Two-Tailed Test: A two-tailed test would be used to test these null hypotheses: There will be no significant difference in IQ scores between males and females.

If you hypothesis is "Experimental model is more than control model", use One-Tailed Test.
If you hypothesis is "Experimental model and control model will not differ very much", use Two-Tailed Test.

This is common for any test, be it T Test, F Test or Chi-square test.

PS.: 1. The one-tailed probability is exactly half the value of the two-tailed probability.
2. Be confident, Statistics is the easiest, once you understand the concepts right.

Answer 2

T test is used when n<30..I am not sure about the 1-tail or 2-tail ..
and for the null hypothesis.. it is to be rejected if the value of t is greater than the value in the table (critical value)... and it is to be accepted if t is less than the critical value...

Answer 3

a million. Use your calculator's Binomial cdf. sort of trials is 80 4 threat of "fulfillment" (i.e. humorous joke) is 0.25 decrease and top values are 19 and 80 4 (i.e. extra advantageous than 18). You get 0.731286 2. A)Use binomial pdf. sort of trials: 7 threat of fulfillment: 9/sixteen x fee: 2 You get 0.106701 B) Use binomial cdf. sort of trials: 7 Prob of fulfillment: 7/sixteen decrease/top values: 0,a million You get 0.114827 C) predicted extensive sort is 9/sixteen * 7 = 3.36. so which you anticipate 3 females, or 3 or 4 females.