The null hypothesis can be stated as follows: "The heights of Q. rubra and Q. alba seedlings are not different three months after germination." There are two alternative hypotheses. "Three months after germination Q. rubra will be taller than Q. alba seedlings," and "Three months after germination Q. rubra will be shorter than Q. alba seedlings." Other wording could be used for any of these statements, as long as the wording precisely conveys the intended meaning.
Before the digital age, statistical calculations had to be done by hand. You won't have to do that, but to understand the rationale behind the test it helps to look at how it was done. First you have to choose a type of t test to run and choose the number of tails. Criteria for making these choices will be presented a little later. Once you have chosen a type there are two steps to conducting "Student's" t test (if you do the calculation by hand). Step one requires that you use the data to generate a number, called a statistic. In this case we calculate a t statistic. The formulas below are for a t test for independent samples, assuming equal variances.
where,
The quantities X, S, and n refer to the mean, standard deviation, and number of data points for a data set. You won't have to do these calculations. Just be aware of how the t statistic is influenced by the data. For example, what happens to the value of t if...
...the difference between means is greater?
...either standard deviation is smaller?
...the total number of data points n is greater?