Regression Calculations
Provide the language for describing "r."
strength of relationship, direction, and shape.
A measurable for a prospective study evaluates the number of new cases for a population at risk
What kind of test statistic evaluates the relationship between groups of categorical data?
Chi Square test statistic.
Find the probability that z > –1
0.8413
An observational study cannot establish ___________, except in only rare circumstances.
Causation.
Provide the interval for "r"
–1 < r < 1
Odds ratios.
Find the degrees of freedom for a chi-square table that has 3 rows by 5 columns.
df: 8
Suppose that the probability that a person over 50 years old chosen at random has high blood pressure is 0.39 and the probability that a person over 50 years old has high blood pressure and is overweight is 0.28. Given that a person over 50 chosen at random has high blood pressure, what is the probability that the person is also overweight?
0.718
Cross-sectional study.
Given the LSRL of y = –2 + 3x, find the residual error for the observed coordinate (4, 20)
10
The probability of testing negative among those who do not have the disease.
Specificity.
Describe the chi-square distribution itself.
Skewed right.
If the data set is normally distributed with a mean of 16 and standard deviation of 3, find the interval for your middle 40% (i.e. the cutoff values).
(14.427, 17.573)
T-Fern believes that ice cream sales are strongly correlated with sunburns, and decides to conduct an observational study. Lily informs him that there's a key confounder, heat, for which he must consider. Explain why heat is a confounder and how that could affect T-Fern's findings.
Heat affects both exposure and outcome; therefore, this lurking variable could distort the data.
On a project where x is defined as the age of a particular type of car in years and y is the Kelly Blue Book value of the vehicle, it is found that the standard deviation of x is 3.5, the standard deviation of y is 4,650 and r = -.91. Interpret the slope in context.
For every year, the value of the car decreased by $1,209.
Among 85 people who developed a disease, 60 of them were exposed to a carcinogen. Among 315 people who did not develop the disease, 175 of them were not exposed to the carcinogen. Find the relative risk for this cohort study.
2.4
Provide the calculation for the test statistic for chi-square goodness of fit.
sum of observed minus expected squared divided by expected.
80% of values are below what value for a normally distributed data set with a mean of 60 and standard deviation of 6.
65.050
How can you raise the power of study? Provide at least one approach to doing so.
Increase sample size, reduce alpha (significance level), use more precise measurements...
Suppose a method of predicting damage of tsunami waves from their destructive force has this LSRL:
log(Damage) = 2 + 0.5 "Destructive Force"
Solve for "Damage."
Damage = 10^(2+ 0.5*DF)
Among 85 people who developed a disease, 60 of them were exposed to a carcinogen. Among 315 people who did not develop the disease, 175 of them were not exposed to the carcinogen. Calculate the odds ratio for this COHORT study.
3.
Provide the formula for expected value of chi square test for independence.
(Row Total x Column Total) / Grand Total
The cutoff for the top 70% is 18 for normally distributed data set with a mean of 24. Find its standard deviation.
11.450
A school has a population that has 800 African-American students and 200 White Students. A study is being done on student perception of the education provided in this school and 80 students are chosen to be in the study, 40 African-Americans and 40 White students. Why is the study problematic?
Bias. We don't know if race is a confounder. there could be other races that are reflected in the population characteristics. You don't have a representative sample.