STT 231 EXAM 1 STUDY GUIDE 2026/2027 ACCURATE QUESTIONS WITH CORRECT DETAILED SOLUTIONS || 100% GUARANTEED PASS NEWEST VERSION

STT 231 EXAM 1 STUDY GUIDE 2026/2027 ACCURATE QUESTIONS WITH CORRECT DETAILED SOLUTIONS || 100% GUARANTEED PASS NEWEST VERSION 1. case - ANSWER observational units 2. participants - ANSWER humans 3. subjects - ANSWER animals 4. ordinal - ANSWER natural order (short, medium, tall) 5. nominal - ANSWER order does not make sense (eye color) 6. categorical variable - ANSWER places an individual into one of several groups or categories (can't be measured) 7. quantitative variable - ANSWER numerical variable 8. how to display categorical data - ANSWER barplot, mosaic plot 9. how to display quantitative data - ANSWER histogram, box plot, scatterplot 10. Mean Statistic symbol - ANSWER x̄ 11. mean parameter symbol - ANSWER μ 12. Proportion statistic symbol - ANSWER p̂ / pi-hat 13. proportion parameter symbol - ANSWER π 14. standard deviation statistic symbol - ANSWER S 15. standard deviation parameter symbol - ANSWER σ 16. statistic vs parameter - ANSWER statistic: describes sample parameter: describes population 17. explanatory variable - ANSWER A variable that helps explain or influences changes in a response variable. 18. response variable - ANSWER A variable that measures an outcome of a study. 19. confounding variable - ANSWER a factor other than the independent variable that might produce an effect in an experiment 20. A study is conducted on students taking a statistic class. Several variables are recorded in the survey. Which variables are quantitative? A. Type of car the student owns B. Number of credit hours taken during that semester C. The time the student waited in line at the bookstore to pay for his/her textbooks D. Home state of the student E. B and C - ANSWER E. B and C 21. A consumer group surveyed the prices for white cotton extra-long twin sheet sets in five different department stores and reported the average price as $16. We visited four of the five stores, and found the prices to be $12, $15, $17, and $22. Assuming that the consumer group is correct, what is the price of the item at the store that we did not visit? A. $10 B. $14 C. $15 D. $17 - ANSWER B. $14 22. (12+15+17+22+14)/5 = 16 Data on the mileage of 20 randomly selected cars is listed below (ordered for convenience) 23. What is the median mileage for these 20 cars? A. 17.5 B. 19 C. 19.5 D. 20 - ANSWER C. 19.5 24. (Lies in the middle of the 20 values) Which is a quantitative variable? A. Salary B. Religious affiliation C. Grams of fat in a cheeseburger D. A and C E. None of these - ANSWER D. A and C 25. How do we define the types of outliers. - ANSWER -Mild outlier if unit exceeds 1.5*IQR -Extreme outlier if unit exceeds 3*IQR When IQR=Q3-Q1 26. What are the mean and standard deviation of z-scores? Will z-scores change the shape of a histogram? - ANSWER -Mean will be 0 and standard deviation will be +1. Will not change shape of histogram. 27. Suppose you were asked about the proportion of data within a certain interval. How would you determine it? - ANSWER -First find the mean and the standard deviation. -Then we can calculate the z-scores for the interval by subtracting each value of the interval by the mean and then dividing by the standard deviation. -According to Chebyshev's rule, we can then say then say z-score="k" and find the proportion of data based on (1-1/k^2) 28. What information can we gather from a scatter plot? - ANSWER -Its direction (positive or negative) -Its form (linear or non-linear) -Its strength (r-value) -unusual features (outliers or clusters) 29. What is the correlation coefficient? Describe its features. - ANSWER Describes linear association between two quantitative variables. -Its units do not matter and it will not change if data is scaled. -It has direction and magnitude: direction is determined by sign and strength is determined by magnitude. -OUTLIER sensitive 30. What are the regression coefficients of the linear regression model? - ANSWER -a=b1 while b=b0 (y=ax+b) -"regression line of Y on X" -"least square regression of Y on X" 31. What are residual values in relation to the linear regression model? - ANSWER -Values explain by how much predicted values deviate from observed Y-values. -If e=0, then there are no errors -If e=+value, then predicted value is an underestimation -If e=-value, then predicted value is an overestimation 32. What is the coefficient of determination? - ANSWER R^2 value. Measures the fraction of total sample variation in y explained by regression model. The larger the value, the better the fit (e.g. 89% of total sample variation is explained by the model).