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How to perform a two-sample t-test?

To conduct a two-sample t-test, follow these steps to ensure clarity and precision in your calculations.

A two-sample t-test is employed to compare the means of two independent samples, helping to ascertain whether they differ significantly. The first step involves calculating the means and standard deviations of both samples.

  1. Calculate the Means and Standard Deviations: Begin by calculating the mean (xˉ1\bar{x}_1 and xˉ2\bar{x}_2) and standard deviation (s1s_1 and s2s_2) for both samples.

  2. Compute the Pooled Standard Deviation: Next, you will calculate the pooled standard deviation (sps_p) using the following formula:

    sp=(n11)s12+(n21)s22n1+n22s_p = \sqrt{\frac{(n_1 - 1)s_1^2 + (n_2 - 1)s_2^2}{n_1 + n_2 - 2}}

    In this formula, s1s_1 and s2s_2 represent the standard deviations of the two samples, while n1n_1 and n2n_2 denote the respective sample sizes.

  3. Calculate the T-Statistic: Following this, compute the t-statistic (tt) using the formula:

    t=xˉ1xˉ2sp1n1+1n2t = \frac{\bar{x}_1 - \bar{x}_2}{s_p \cdot \sqrt{\frac{1}{n_1} + \frac{1}{n_2}}}

    Here, xˉ1\bar{x}_1 and xˉ2\bar{x}_2 are the means of the two samples, n1n_1 and n2n_2 are the sample sizes, and sps_p is the pooled standard deviation.

  4. Determine the Degrees of Freedom: Next, calculate the degrees of freedom (dfdf) using the formula:

    df=n1+n22df = n_1 + n_2 - 2
  5. Find the P-Value: Finally, consult a t-distribution table or utilize a calculator to determine the p-value corresponding to your calculated t-statistic and degrees of freedom. If the p-value is less than your predetermined significance level (typically set at 0.050.05), this indicates that the means of the two samples are significantly different from one another.

By following these steps, you will effectively perform a two-sample t-test and interpret its results accurately.

Answered by: Prof. David Martin
A-Level Physics Tutor
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