statistics 4

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Questions and Answers

In biomedical research, when analyzing the relationship between two categorical variables, the predictor variable (X-axis) influences the subjects by:

Causing a direct linear change in a Y parameter, such as blood pressure.

Causing subjects to fall into two or more categories of outcome. (correct)

Increasing the mean value of a continuous variable.

Decreasing the variance within a specific group.

Contingency tables are used to display results of analyses involving a continuous variable on the Y axis and a categorical variable on the X axis.

False (B)

If you are analyzing the relationship between adding sugar to coffee (yes/no) and energy levels (high/low), which statistical test is most appropriate?

Chi-squared test

When assessing how gender influences the likelihood of having an HIV test, the results are typically displayed in a __________ table.

contingency Signup and view all the answers

Match each statistical test with its appropriate variable types:

T-test = Continuous Y axis, 2 Categories on X axis ANOVA = Continuous Y axis, 3 or more Categories on X axis Chi-squared test = Categorical Y axis, Categorical X axis Signup and view all the answers

In a Chi-squared test, what does the `CHISQ.TEST` function in Excel return?

The p-value (A) Signup and view all the answers

In a Chi-squared test performed in Excel, the observed data should be specified as the second argument in the `CHISQ.TEST` function.

False (B) Signup and view all the answers

When calculating the expected value for a cell in a Chi-squared test, what formula is used?

(Row Total * Column Total) / Grand Total Signup and view all the answers

In a Chi-squared test, if the p-value is less than the significance level, we ______ the null hypothesis.

reject Signup and view all the answers

Match the terms with their descriptions in the context of a Chi-squared test:

Observed Values = The actual data collected from the sample. Expected Values = Values calculated based on the assumption that the null hypothesis is true. P-value = Probability of obtaining test results at least as extreme as the results actually observed, assuming that the null hypothesis is correct. Grand Total = Sum of all observed data. Signup and view all the answers

Fisher's exact test is frequently used in biomedicine due to the typically large sample sizes encountered.

False (B) Signup and view all the answers

When should Fisher's exact test be used instead of the Chi-squared test?

When at least one cell in the contingency table has an expected count less than 5. (D) Signup and view all the answers

If a researcher wants to determine if there's a statistically significant association between different drug dosages and disease recovery using a contingency table, but only wants an overall significance, which statistical tests can be used?

Chi-squared test or Fisher's exact test Signup and view all the answers

For contingency tables larger than 2x2, the Chi-squared test or Fisher's exact test will indicate if at least ______ condition is significant, but not the specific condition.

one Signup and view all the answers

Which software packages are suitable for performing Fisher's exact test when Excel lacks the functionality?

R, Jamovi, and SPSS (D) Signup and view all the answers

A statistically significant result from a Chi-squared test on a larger contingency table (e.g., 4x2) pinpoints exactly which conditions are significantly different from each other. In other words, the test identifies WHICH specific conditions stick out.

False (B) Signup and view all the answers

Match the scenario with the appropriate condition for using Fisher's exact test:

Grand total exceeds 50, every observation exceeds 5 = Not suitable Grand total is 14, every cell is less than 5 = Use Fisher's exact test Grand total is 378, one cell is less than 5 = Use Fisher's exact test Grand total is 378, every cell exceeds 50 = Not suitable Signup and view all the answers

Consider a 2x2 contingency table. Which scenario necessitates the use of Fisher's exact test?

The grand total of all observations is less than 50 and at least one expected cell count is less than 5. (A) Signup and view all the answers

If the 95% confidence interval (CI) for an Odds Ratio (OR) includes 1, what does this indicate?

The result is not statistically significant. (D) Signup and view all the answers

A log(OR) of 1 indicates there is 'no effect'.

False (B) Signup and view all the answers

What is the primary reason Fisher's exact test is used instead of Pearson's chi-squared test in certain situations?

Small sample sizes Signup and view all the answers

For Pearson's chi-squared test to be appropriate, the grand total of observations must exceed ______.

50 Signup and view all the answers

What value represents 'no effect' when using Log(OR)?

0 (C) Signup and view all the answers

Why was the Chi-squared test developed?

To simplify calculations when dealing with large numbers, which can be computationally intensive in Fisher's exact test. (C) Signup and view all the answers

Fisher’s exact test is an approximation, and the Chi-squared test provides the exact p-value.

False (B) Signup and view all the answers

Under what condition should you not use the Chi-squared test and instead opt for Fisher's exact test?

When the grand total of observations is below 50 and/or any cell count is less than 5. (C) Signup and view all the answers

In a Chi-squared test, what does an odds ratio greater than 1 suggest?

The exposure is positively associated with the outcome. (B) Signup and view all the answers

In an expected value table for a Chi-squared test, it is acceptable to have fractional values even if the observed data consists of whole numbers.

True (A) Signup and view all the answers

What statistical software packages are mentioned as tools that eliminate the need to manually look up p-values from a Chi-squared distribution table?

R and Excel Signup and view all the answers

In the context of the provided example, the odds of passing the exam after having lunch are calculated as 35/15, which equals ______.

2.3 Signup and view all the answers

If the odds of passing an exam after a meal are 2.3 and the odds of passing before a meal are 1.5, what is the odds ratio?

1.53 (B) Signup and view all the answers

In a Chi-squared test, an odds ratio of exactly 1 between two variables indicates that there is a strong association between them.

False (B) Signup and view all the answers

In the context of a Chi-squared test, what is the purpose of creating an 'expected value table'?

To determine what the values would be if there is no association between the variables. Signup and view all the answers

What does a Relative Risk (RR) of 1 indicate between two conditions?

No difference in risk between the two conditions. (D) Signup and view all the answers

The odds ratio (OR) is calculated by dividing the risk of an event in one group by the total number of events.

False (B) Signup and view all the answers

What is the purpose of using the Chi-squared test in the context of analyzing contingency tables?

to test for significance Signup and view all the answers

In hypothesis testing, a p-value is used to determine the statistical ______ of an observed result.

significance Signup and view all the answers

Match the statistical measure with its appropriate interpretation:

Odds Ratio (OR) = The ratio of the odds of an event occurring in one group versus another. Relative Risk (RR) = The ratio of the probability of an event occurring in an exposed group versus a non-exposed group. Chi-squared test = A test to determine if there is a significant association between two categorical variables. Signup and view all the answers

Why is it important to test the odds ratio (OR) for significance?

To determine if the observed OR is likely due to chance. (B) Signup and view all the answers

Expected values in a Chi-squared test represent the values you would expect to see if there is an effect.

False (B) Signup and view all the answers

In the context of the Chi-squared test, what do observed values represent?

actual counts Signup and view all the answers

Karl Pearson, known for his work on the correlation coefficient, also developed the significance test for ______ tables.

contingency Signup and view all the answers

How does the magnitude of the Chi-squared value relate to the significance of the difference between observed and expected values?

A larger Chi-squared value indicates a more significant difference. (B) Signup and view all the answers

When is Fisher's Exact Test most appropriate compared to the Chi-Squared test?

When sample sizes are small or expected cell counts are less than 5. (B) Signup and view all the answers

A high p-value (e.g., above 0.05) indicates a statistically significant association between the variables being tested.

False (B) Signup and view all the answers

What distribution does Fisher’s Exact Test use to calculate probabilities, instead of approximating with a Chi-Squared distribution?

hypergeometric distribution Signup and view all the answers

Ideally, the expected counts in each cell for a Chi-Squared test should be ________ or more to ensure a good approximation.

5 Signup and view all the answers

Match the statistical test with its appropriate condition for use:

Chi-Squared Test = Large samples with adequate expected frequencies. Fisher’s Exact Test = Small samples or sparse data. Signup and view all the answers

Which of the following is a key assumption for the Chi-Squared test?

The observations should be independent. (D) Signup and view all the answers

In a 2x2 contingency table, what does Fisher's Exact Test calculate?

The exact probability of observing a table as extreme or more extreme, given no association. (C) Signup and view all the answers

In the context of hypothesis testing, what does a low Chi-Squared statistic, resulting in a high p-value, generally indicate?

no significant association Signup and view all the answers

In a Chi-Squared test for a 2x2 table, what does the test primarily assess?

The statistical significance of an association between two categorical variables. (D) Signup and view all the answers

The expected counts in a Chi-Squared test represent the values you would expect to see if there were a strong association between the variables.

False (B) Signup and view all the answers

Write the formula to calculate the expected count for a cell in a Chi-Squared test.

(Row Total * Column Total) / Grand Total Signup and view all the answers

In the Chi-Squared test calculation, the term `(Observed - Expected)^2 / Expected` represents the contribution of each ______ to the overall Chi-Squared statistic.

cell Signup and view all the answers

For a standard 2x2 contingency table, what is the degrees of freedom for the Chi-Squared test?

1 (D) Signup and view all the answers

A small p-value in a Chi-Squared test suggests there is a weak association between the categorical variables.

False (B) Signup and view all the answers

Given a 2x2 table where Group 1 total is 50, Category A total is 60, and the Grand Total is 100, what is the expected count for Group 1, Category A?

30 Signup and view all the answers

Flashcards

T-test

A statistical test used for comparing means between two categories.

ANOVA

Analysis of Variance; a method for comparing three or more groups.