Find a published research study on a topic that you could use for your DNP project that used an independent t-test and find this information from the study:
Give the purpose/objective/aim of the study exactly as it is written in the study.
What is the population in the study?
What is the independent (treatment or intervention) variable?
What is the dependent (outcome) variable? If there are multiple dependent variables, choose only one for the focus of this discussion. What is its
level of measurement (nominal, ordinal, interval, ratio)? Is it a categorical or continuous variable? You can often determine this as you read the Methods section of the report.
If a hypothesis was stated in the article for the independent t-test, give it here and label it as a Ho or Ha. Write the stated hypothesis as an equation. Write the other hypothesis (the Ho or Ha that was not given) in words and an equation. If a hypothesis was not stated, then restate the purpose/objective/aim as a null hypothesis in words and equation format. Do this for both a null and alternative hypothesis. Again, focus on only one independent variable and one dependent variable. Use the format on pp. 217-218 of Kim et al. (2022) and the handout attached to the announcement for this week.
What are the assumptions for the independent t-test (Kim et al., 2022, p. 217)? Are they met in this study? Provide information given in the study that can be used to determine whether each assumption is or is not met. What information is not given?
What alpha level (level of significance) was used?
What are the groups that were tested?
Give the mean values with the standard deviation for the outcome variable for the groups.
Give the t-statistic, if provided, and p-value for the difference in mean values for the DV you are focusing on.
Specifically state the p-value rule for the results of this study to determine whether to reject or fail to reject the null hypothesis.
Based on the decision made about the null hypothesis, what type of error is possible (Kim et al., 2022, pp. 131-132 and Table 7-3).
What are the usual causes of this type of error? Are any of them present in the methodology for this study?
Give the confidence interval for the difference in mean values, if provided. Use the confidence interval around a difference in mean values rule (given in the Overview in Module 5) to determine whether to reject or fail to reject the null hypothesis.
The effect size for t-test results is reported as a Cohen’s d statistic (Kim et al., (2022, p. 134). Give this value, if given in the study, and interpret what it means (use the guidelines in the Overview in Module5) in terms of the magnitude or clinical meaningfulness (clinical significance) of the result. If not given, determine the clinical significance of the difference in mean values by using your knowledge, critical thinking, and experience with your patients and setting, would you incorporate the intervention or treatment into your practice? Is your evaluation of the clinical significance of the findings consistent with the statistical significance for the findings and the value of the effect size? Explain your rationale.
Find a published research article the used a paired t-test to test the difference in mean values at two different times.
State the null and alternative hypotheses in words and an equation for the outcome variable. You will need to write this from the purpose/objective/aim if a hypothesis is not given.
Describe the two times the dependent (outcome) variable was measured.
Give the two mean values for the outcome variable for the two times.
Give the t-statistic and p-value for the difference in mean values.
Specifically state the p-value rule to determine whether to reject or fail to reject the null hypothesis
Full Answer Section
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Hypotheses:
- H₀: There is no significant difference in mean anxiety levels between the mindfulness-based intervention group and the control group. μ₁ - μ₂ = 0
- Ha: There is a significant difference in mean anxiety levels between the mindfulness-based intervention group and the control group. μ₁ - μ₂ ≠ 0
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Assumptions:
- Independence: Observations within each group and between groups are independent. Information Given: The study states participants were randomly assigned to groups. Information Not Given: Details about how the intervention was delivered and whether there was any potential for cross-contamination between groups.
- Normality: Anxiety levels in each group are approximately normally distributed. Information Given: The study mentions using a Shapiro-Wilk test to assess normality. Information Not Given: The actual results of the normality test (e.g., p-values). Often, if sample sizes are large enough (generally >30 per group), the t-test is robust to minor violations of normality due to the Central Limit Theorem.
- Equal Variances (Homogeneity of Variance): The variances of anxiety levels are equal between the two groups. Information Given: The study mentions using Levene's test for equality of variances. Information Not Given: The results of Levene's test (e.g., p-value).
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Alpha Level: α = 0.05 (commonly used).
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Groups: Mindfulness-based intervention group and control group.
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Means and Standard Deviations: Mindfulness group: M = 35, SD = 5; Control group: M = 40, SD = 7.
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t-statistic and p-value: t = 2.5, p = 0.02.
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p-value Rule: If the p-value is less than the alpha level (0.05), reject the null hypothesis.
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Type I Error: Because the p-value is less than 0.05, the null hypothesis is rejected. A Type I error (false positive) is possible. This means the study found a statistically significant difference when, in reality, no true difference exists in the population.
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Causes of Type I Error: Small sample size, random chance, researcher bias, or problems with the study design/methods. Information Given: The study had a sample size of 60 (30 in each group). This is reasonably good to assume normal distribution. Information Not Given: No information on researcher bias or study design.
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Confidence Interval: 95% CI for the difference in means: [1, 9].
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CI Rule: If the confidence interval for the difference in means does not include zero, reject the null hypothesis. Since the CI [1,9] does not include zero, we reject the null hypothesis.
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Cohen's d: d = 0.6. This is considered a moderate effect size, suggesting the mindfulness intervention had a practically meaningful impact on anxiety levels.
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Clinical Significance: Based on the moderate effect size and the statistically significant results, the mindfulness intervention appears to have a clinically meaningful impact on reducing anxiety. Given the potential benefits and low risk, it would be reasonable to incorporate this intervention into practice. The evaluation of clinical significance aligns with the statistical significance and effect size.
Part 2: Paired Samples t-test
Example Research Question (Hypothetical): Does a pre-operative education session reduce patient anxiety levels before surgery?
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Hypotheses:
- H₀: There is no significant difference in mean anxiety levels before and after the pre-operative education session. μd = 0
- Ha: There is a significant difference in mean anxiety levels before and after the pre-operative education session. μd ≠ 0
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Times of Measurement: Anxiety level (measured using the STAI) was assessed before the education session and again after the session.
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Mean Values: Before: M = 45, After: M = 40.
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t-statistic and p-value: t = 3.0, p = 0.005.
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p-value Rule: If the p-value is less than the alpha level (0.05), reject the null hypothesis.
Remember to replace the hypothetical examples with information from your chosen research articles. Pay close attention to the details provided in the methods and results sections to answer the questions accurately.
Sample Answer
Let's break down how to analyze research studies using t-tests. I'll provide a general framework and examples, as I cannot access external research articles. You'll need to apply this to the specific articles you find.
Part 1: Independent Samples t-test
Example Research Question (Hypothetical): Does a mindfulness-based intervention reduce anxiety levels in nursing students compared to a control group?
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Purpose/Objective/Aim: To evaluate the effectiveness of a mindfulness-based intervention on reducing anxiety levels in nursing students.
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Population: Nursing students enrolled in a Bachelor of Science in Nursing program at [University Name].
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Independent Variable: Type of intervention (mindfulness-based intervention vs. control group).
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Dependent Variable: Anxiety level, measured using the State-Trait Anxiety Inventory (STAI). Level of Measurement: Interval. Continuous variable.