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Inferential Statistics Techniques

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Log-Rank Test

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Used to compare survival distributions of two samples. Formula: The calculation involves event times and survival probabilities, but exact formula is complex and often done with specialized survival analysis software.

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Pearson Correlation Coefficient

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Measures the linear relationship between two continuous variables. Formula:

r=(xixˉ)(yiyˉ)(xixˉ)2(yiyˉ)2r = \frac{\sum (x_i - \bar{x})(y_i - \bar{y})}{\sqrt{\sum (x_i - \bar{x})^2 \sum (y_i - \bar{y})^2}}
where \(x_i\) and \(y_i\) are the values of the two variables.

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Confidence Interval for Mean

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Estimates the interval in which the population mean is likely to lie with a certain level of confidence. Formula for large sample sizes (n>30n>30):

Xˉ±Zασn\bar{X} \pm Z_\alpha\frac{\sigma}{\sqrt{n}}
Formula for small sample sizes (n30n \le 30):
Xˉ±tαsn\bar{X} \pm t_\alpha\frac{s}{\sqrt{n}}
where \(\bar{X}\) is the sample mean, \(\sigma\) and \(s\) are the population and sample standard deviations, respectively, and \(n\) is the sample size.

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Paired T-Test

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Compares means of two related groups (e.g., before-after, matched pairs), used with small sample sizes. Formula:

t=dˉsd/nt = \frac{\bar{d}}{s_d/\sqrt{n}}
where \(\bar{d}\) is the mean of the differences and \(s_d\) is the standard deviation of the differences.

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Wilcoxon Signed-Rank Test

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Compares two related samples to assess differences in their population mean ranks. Formula: The test statistic is based on the sum of signed ranks, but the formula is complex and typically done with software.

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T-Test for Mean (One-sample)

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Used when the sample size is small (n30n \le 30), population variance is unknown, and the data is approximately normally distributed. Formula:

t=Xˉμs/nt = \frac{\bar{X} - \mu}{s/\sqrt{n}}
where \(\bar{X}\) is the sample mean, \(\mu\) is the population mean, \(s\) is the sample standard deviation, and \(n\) is the sample size.

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Chi-Square Test for Independence

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Determines if there is a significant association between two categorical variables. Formula:

χ2=(OE)2E\chi^2 = \sum \frac{(O - E)^2}{E}
where \(O\) represents the observed frequency and \(E\) represents the expected frequency under the null hypothesis.

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Mann-Whitney U Test

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Compares differences between two independent groups when the assumptions for the t-test are not met (e.g., non-normal distributions). Formula: The calculation involves ranking all observations and computing U based on these ranks, but the exact formula is complex and often calculated with software.

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Kruskal-Wallis Test

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Non-parametric version of ANOVA, used for comparing three or more independent samples of different sizes. Formula:

H=12N(N+1)Ri2ni3(N+1)H = \frac{12}{N(N+1)}\sum \frac{R_i^2}{n_i} - 3(N+1)
where \(N\) is the total number of observations, \(R_i\) is the sum of ranks for the ith group, and \(n_i\) is the number of observations in the ith group.

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T-Test for Independent Samples

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Compares means of two independent groups, used when variances are unknown but assumed to be equal, sample sizes may be unequal. Formula:

t=Xˉ1Xˉ2sp1n1+1n2t = \frac{\bar{X}_1 - \bar{X}_2}{s_p\sqrt{\frac{1}{n_1} + \frac{1}{n_2}}}
where \(s_p\) is the pooled standard deviation.

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One-Way ANOVA

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Tests if there are any statistically significant differences between the means of three or more independent (unrelated) groups. Formula:

F=MSbetweenMSwithinF = \frac{MS_{between}}{MS_{within}}
where \(MS_{between}\) and \(MS_{within}\) are the mean squares between and within groups.

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Z-Test for Mean

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Used when sample size is large (n>30n>30), population variance is known, and data is normally distributed. Formula:

z=Xˉμσ/nz = \frac{\bar{X} - \mu}{\sigma/\sqrt{n}}
where \(\bar{X}\) is the sample mean, \(\mu\) is the population mean, \(\sigma\) is the population standard deviation, and \(n\) is the sample size.

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Two-Way ANOVA

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Tests the effect of two independent categorical variables on a continuous outcome variable. Formula: It involves computing F-statistics for each variable and their interaction, but the formula is complex and beyond the scope of a flashcard.

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Simple Linear Regression

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Evaluates the linear relationship between two continuous variables. Formula:

y=β0+β1xy = \beta_0 + \beta_1x
where \(y\) is the dependent variable, \(x\) is the independent variable, \(\beta_0\) is the intercept, and \(\beta_1\) is the slope.

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Spearman's Rank Correlation Coefficient

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Measures the strength and direction of the association between two ranked variables. Formula:

rs=16di2n(n21)r_s = 1 - \frac{6\sum d_i^2}{n(n^2 - 1)}
where \(d_i\) is the difference between the ranks of each observation, and \(n\) is the number of observations.

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