Calculating the Estimated Difference

Oct 13, 2025 by wbrum.org 130 views

Introduction

In statistics, comparing two sample means is a crucial aspect of hypothesis testing and confidence interval estimation. This article will guide you through the process of estimating the difference in two sample means using the given sample data. We will use the provided sample means, sizes, and standard deviations to calculate the estimated difference in the two sample means.

Given Data

Two samples are taken with the following sample means, sizes, and standard deviations:

Sample	Mean ( $\bar{x}$ )	Size ( $n$ )	Standard Deviation ( $s$ )
1	20	50	2
2	38	53	3

Calculating the Estimated Difference

To estimate the difference in the two sample means, we will use the following formula:

\bar{x}_1 - \bar{x}_2 = \text{Estimated Difference}

where $\bar{x}_1$ and $\bar{x}_2$ are the sample means of the two samples.

Plugging in the given values, we get:

20 - 38 = -18

Therefore, the estimated difference in the two sample means is -18.

Calculating the Standard Error

The standard error (SE) is a measure of the variability of the estimated difference. It is calculated using the following formula:

SE = \sqrt{\frac{s_1^2}{n_1} + \frac{s_2^2}{n_2}}

where $s_1$ and $s_2$ are the standard deviations of the two samples, and $n_1$ and $n_2$ are the sample sizes.

Plugging in the given values, we get:

SE = \sqrt{\frac{2^2}{50} + \frac{3^2}{53}}

SE = \sqrt{\frac{4}{50} + \frac{9}{53}}

SE = \sqrt{0.08 + 0.1695}

SE = \sqrt{0.2495}

SE = 0.499

Calculating the Margin of Error

The margin of error (ME) is a measure of the maximum amount by which the estimated difference may differ from the true difference. It is calculated using the following formula:

ME = SE \times Z_{\alpha/2}

where $Z_{\alpha/2}$ is the critical value from the standard normal distribution corresponding to the desired confidence level.

Assuming a 95% confidence level, we get:

Z_{\alpha/2} = 1.96

ME = 0.499 \times 1.96

ME = 0.978

Conclusion

In conclusion, the estimated difference in the two sample means is -18, with a standard error of 0.499 and a margin of error of 0.978. This means that we are 95% confident that the true difference in the two sample means lies within the range of -18 ± 0.978.

Discussion

The results of this analysis suggest that there is a significant difference between the two sample means. The estimated difference of -18 indicates that the mean of sample 1 is lower than the mean of sample 2. This difference is statistically significant, as indicated by the margin of error.

Limitations

This analysis has several limitations. Firstly, the sample sizes are relatively small, which may affect the accuracy of the results. Secondly, the standard deviations of the two samples are different, which may affect the calculation of the standard error.

Future Research

Future research could involve increasing the sample sizes to improve the accuracy of the results. Additionally, the analysis could be extended to include other variables that may affect the relationship between the two sample means.

References

[1] Moore, D. S., & McCabe, G. P. (2013). Introduction to the practice of statistics (6th ed.). W.H. Freeman and Company.
[2] Larson, R. E., & Farber, B. A. (2014). Elementary statistics: Picturing the world with statistics (5th ed.). Cengage Learning.

Appendix

The following is a summary of the calculations performed in this analysis:

Calculation	Formula	Value
Estimated Difference	$\bar{x}_1 - \bar{x}_2$	-18
Standard Error	$\sqrt{\frac{s_1^2}{n_1} + \frac{s_2^2}{n_2}}$	0.499
Margin of Error	$SE \times Z_{\alpha/2}$	0.978

Q: What is the purpose of comparing two sample means?

A: The purpose of comparing two sample means is to determine if there is a significant difference between the means of two groups or populations. This can be useful in a variety of fields, such as medicine, social sciences, and business.

Q: What are the assumptions of the two-sample t-test?

A: The assumptions of the two-sample t-test are:

The data are normally distributed
The data are independent
The variances of the two samples are equal (homoscedasticity)
The sample sizes are sufficiently large

Q: What is the difference between a two-sample t-test and a two-sample z-test?

A: A two-sample t-test is used when the sample sizes are small (less than 30) or when the population standard deviation is unknown. A two-sample z-test is used when the sample sizes are large (greater than 30) and the population standard deviation is known.

Q: How do I choose between a two-sample t-test and a two-sample z-test?

A: To choose between a two-sample t-test and a two-sample z-test, you need to determine the sample size and the population standard deviation. If the sample size is small or the population standard deviation is unknown, use a two-sample t-test. If the sample size is large and the population standard deviation is known, use a two-sample z-test.

Q: What is the formula for the two-sample t-test?

A: The formula for the two-sample t-test is:

t = \frac{\bar{x}_1 - \bar{x}_2}{\sqrt{\frac{s_1^2}{n_1} + \frac{s_2^2}{n_2}}}

where $\bar{x}_1$ and $\bar{x}_2$ are the sample means, $s_1$ and $s_2$ are the sample standard deviations, and $n_1$ and $n_2$ are the sample sizes.

Q: What is the critical value for the two-sample t-test?

A: The critical value for the two-sample t-test depends on the sample size, the population standard deviation, and the desired level of significance. You can use a t-distribution table or a statistical software package to find the critical value.

Q: How do I interpret the results of a two-sample t-test?

A: To interpret the results of a two-sample t-test, you need to examine the p-value and the confidence interval. If the p-value is less than the desired level of significance, you can reject the null hypothesis and conclude that there is a significant difference between the two sample means. If the p-value is greater than the desired level of significance, you cannot reject the null hypothesis and conclude that there is no significant difference between the two sample means.

Q: What are some common mistakes to avoid when performing a two-sample t-test?

A: Some common mistakes to avoid when performing a two-sample t-test include:

Not checking the assumptions of the test
Not using the correct formula or software
Not interpreting the results correctly
Not considering the sample size and population standard deviation

Q: Can I use a two-sample t-test for non-normal data?

A: No, you cannot use a two-sample t-test for non-normal data. The two-sample t-test assumes that the data are normally distributed. If the data are not normally distributed, you may need to use a non-parametric test or a transformation to make the data more normal.

Q: Can I use a two-sample t-test for paired data?

A: No, you cannot use a two-sample t-test for paired data. The two-sample t-test assumes that the data are independent. If the data are paired, you may need to use a paired t-test or a non-parametric test.