T- TEST ( Dependent and Independent

T- TEST

(Dependent and Independent

​PRACTICAL RESEARCH 2

BWS SHS​

NEOLMS REFERENCE​

GO TO NEOLMS MODULE 3

READ SECTION 5 AND 6

Some text here about the topic of discussion

Dependent t-test

Note that dof is computed using (npairs -1)

Used when:

1.A comparison of the pretest and posttest scores of the same participants.

2.A comparison of the scores of one group of participants with another group of participants who are matched on one or more extraneous variables​

​

Dependent t-test

Note that dof is computed using (npairs -1)

Used when:

3. A comparison of the scores of the same group of participants under two different conditions.

4. A comparison of the scores of naturally occurring correlated pairs, like twins.

Sample problem

A researcher wants to compare pretest scores with posttest scores on self-compassion from the same 16 participants who received a mindfulness treatment program. Self-compassion is measured by the Self-Compassion Scale (SCS; Neff, 2003), and high scores reflect higher self-compassion.

Multiple Select

How should the hypotheses be written?

• H_a: μ_prescs ≠μ _postscs

• H₀: μ_prescs ≠μ _postscs

• H_a: μ_prescs < μ _postscs

• H₀: μ_prescs =μ _postscs

Multiple Choice

If alpha is set at .05 for a two-tailed test and n pairs is 16, what is the critical value?

• ±2.120

• ±2.131

• ±1.753

• ±1.746

Fill in the Blanks

With:

N =16

Dbar = -26.13

ΣD ⁼ - 418

ΣD² = 15,334

Solve for t stat

Multiple Choice

After comparing the critical value with the computed statistic, the null hypothesis ____

• is rejected.

• cannot be rejected

• is insufficient.

Practice

Suppose a sample of n students were given a diagnostic test before studying a particular module and then again after completing the module. We want to find out if, in general, our teaching leads to improvements in students’ knowledge/skills (i.e. test scores).

Compute for t stat

Dbar = 2.05

Σ D = 41

Σ D ^{2 =} 237

N =20

α =.02

Fill in the Blanks

How should the null and alternative hypotheses be written?

Fill in the Blanks

What is the computed t stat?

Fill in the Blanks

What is the critical value for a two-tailed test with an alpha of .02 and Npairs =20

Fill in the Blanks

After comparing the critical value and the t-stat, the null hypothesis is

Independent T test

The independent t-test is used to test if two sample means are significantly different from each other from two independent samples. This is a between-group analysis. We are testing whether the two means from independent samples are from different populations. The sample means as estimators of the population parameters based upon the sampling distribution of differences between means.

Independent T test

Note that for the independent t-test, the VARIANCE is used instead of the standard deviation. The variance is the square of the standard deviation.

Sample Problem

An independent t-test analysis will be demonstrated comparing a randomly assigned group of 16 participants who received a psychotherapy intervention on their changes in thought suppression to a control group (n=16) who received the treatment later. Thought suppression is measured using the White Bear Suppression Inventory (WBSI) (Wegner & Zanakos, 1994), and high scores represent higher perceived thought suppression.

Multiple Select

How should the hypotheses be written?

• H₀: μ_{psychotherapy}=μ_control

• H_a: μ_{psychotherapy}=μ_control

• H_a: μ_{psychotherapy}≠μ_control

• H₀: μ_{psychotherapy>}μ_control

Fill in the Blanks

If alpha is .02, and n1= 16 and n2= 16, what is the critical value?

Fill in the Blanks

With the given:

X = 39.75, s2 = 95.67, n=16, and for the control group X = 53.06, s2 = 130.73, n=16.

Solve for tstat

Fill in the Blanks

After comparing the computed stat with the critical value, the decision is to:

Practice Problem

Researchers want to examine the effect of perceived control on health complaints of geriatric patients in a long-term care facility. Thirty patients are randomly selected to participate in the study. Half are given a plant to care for and half are given a plant but the care is conducted by the staff. Number of health complaints are recorded for each patient over the following seven days. Compute the appropriate t-test

Fill in the Blanks

Mean1 (self care for plants) = 16.67

S² = 60.68571

Mean2 (staff care for plants)= 27.067

S² = 59.92380952

n1= 15

n2=15

α =0.05

Compute for critical value

Fill in the Blanks

Mean1 (self care for plants) = 16.67

S² = 60.68571

Mean2 (staff care for plants)= 27.067

S² = 59.92380952

n1= 15

n2=15

α =0.05

Compute t stat

Multiple Choice

After comparing t stat with critical value, the null

• should be rejected

• cannot be rejected