Which of the following statements concerning research method

Which of the following statements concerning research methods and t-tests are accurate (Give ALL correct answers)

1-- True False  An independent groups t-test can not be used if the independent variable is simply observed rather than manipulated.

2-- True False  Limiting your sample to include only a certain type of person (e.g., only women or only average intelligence children), has the disadvantage of increasing variation within treatment groups.

3-- True False  In order to make cause and effect conclusions, random assignment must be used in an experiment.

4-- True False  In an independent groups t-test, the null hypothesis is that the two population means are equal.

Solution

(1) False

(2)True

(3)False

(4)True