Suppose you have two random variables X,Y ux,Hy,o o3,0xY where Cov(X, Y) = 0x.Y You sample both (1poume n is very very very large.) 5

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Statistics in Science

### Statistical Analysis of Two Random Variables

Suppose you have two random variables \( X, Y \) with the following properties:

\[ X, Y \sim \mu_X, \mu_Y; \sigma_X^2, \sigma_Y^2, \sigma_{XY} \]

where \( \text{Cov}(X, Y) = \sigma_{XY} \).

### Sampling

You sample both and observe:

\[ (x_1, y_1), \ldots, (x_n, y_n) \]

Assume \( n \) is very large.

### Constructing a Test Statistic

Construct a test statistic, \( Z \), for the difference in means \( \mu_X - \mu_Y \), by:

\[ Z = \frac{(\bar{x} - \bar{y}) - \mathbb{E}(\mu_X - \mu_Y)}{\sqrt{\text{Var}(\bar{X} - \bar{Y})}} \]

### Assignment

Complete this equation in terms of the parameters of the original random variables and the sample size \( n \).

### Example Calculation

Suppose you observe sample data:
- \( n = 81, \bar{x} = 50, \bar{y} = 55 \)
- Known values: \( \sigma_X^2 = 25, \sigma_Y^2 = 144, \sigma_{XY} = 34.5 \)

### Hypothesis Testing

Test a two-sided hypothesis that there is no difference in the means of \( X \) and \( Y \).
Transcribed Image Text:### Statistical Analysis of Two Random Variables Suppose you have two random variables \( X, Y \) with the following properties: \[ X, Y \sim \mu_X, \mu_Y; \sigma_X^2, \sigma_Y^2, \sigma_{XY} \] where \( \text{Cov}(X, Y) = \sigma_{XY} \). ### Sampling You sample both and observe: \[ (x_1, y_1), \ldots, (x_n, y_n) \] Assume \( n \) is very large. ### Constructing a Test Statistic Construct a test statistic, \( Z \), for the difference in means \( \mu_X - \mu_Y \), by: \[ Z = \frac{(\bar{x} - \bar{y}) - \mathbb{E}(\mu_X - \mu_Y)}{\sqrt{\text{Var}(\bar{X} - \bar{Y})}} \] ### Assignment Complete this equation in terms of the parameters of the original random variables and the sample size \( n \). ### Example Calculation Suppose you observe sample data: - \( n = 81, \bar{x} = 50, \bar{y} = 55 \) - Known values: \( \sigma_X^2 = 25, \sigma_Y^2 = 144, \sigma_{XY} = 34.5 \) ### Hypothesis Testing Test a two-sided hypothesis that there is no difference in the means of \( X \) and \( Y \).
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