Data Analysis Flashcards

Of 80 students who play sports, 60 get good grades. Of 120 who don't play sports, 40 get good grades. What fraction of all 200 students get good grades?

Answer: 1/2

Total with good grades = 60 + 40 = 100 out of 200 students = 100/200 = 1/2.

A city's population was 50,000 in 2000 and 80,000 in 2020. What was the percent increase over this period?

Answer: 60%

Percent increase = (80,000 − 50,000)/50,000 × 100 = 30,000/50,000 × 100 = 60%.

A random sample of 500 voters shows 55% support a ballot measure, but the true population support is 52%. What best explains the 3-point difference?

Answer: The difference is due to sampling variability

Random samples naturally vary from the true population value; this difference is expected sampling variability.

Annual sales (in millions) over four years: $4M, $6M, $5M, $8M. What is the mean annual sales?

Answer: $5.75M

Mean = (4 + 6 + 5 + 8) / 4 = 23 / 4 = $5.75M.

A study reports a drug reduces cholesterol by an average of 15 points with a p-value of 0.03. Which conclusion is most appropriate?

Answer: The result is statistically significant at the 0.05 level

A p-value of 0.03 is less than 0.05, so the result is statistically significant at the 5% significance level.

A histogram is right-skewed. Which statement about its mean and median is most likely true?

Answer: Mean > Median

In a right-skewed distribution, the long right tail pulls the mean above the median.

Ice cream sales and drowning rates both rise in summer. A reporter claims ice cream causes drowning. What is the flaw in this reasoning?

Answer: Hot weather is a confounding variable causing both to rise

Hot weather drives both ice cream consumption and swimming activity, making temperature the confounding variable.