1. What is categorical data?
    • Data that fits into categories.
    • It can be nominal (no order implied): Race: Black, White, other
    • or ordered: income: < $20k, $20k-$80k, > $80k.
  2. How do you calculate variance and standard deviation?
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    • Where x bar = average, n = sample size, x2 = sample, and S2 = variance.
    • The standard deviation, S, is the square root of the variance.
  3. What is a normal distribution?
    aka Gaussian distribution, it is simply a symmetrical bell shaped distribution where the mean, median, and mode are all the same number.
  4. What is the standard normal distribution?
    • A normal distribution with a mean of 0 and a standard deviation of 1.  68% of data are within one standard deviation, 95% are within 2 standard deviations, and 99.7% are within 3.
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  5. How can we appraise the normal distribution of a graph?
    • A histogram compares the distribution with a standard deviation curve so you can see how much they deviate from one another.
    • A Q-Q plot compares the individual samples to the average, denoted as a diagonal line (the average) and dots (the individual samples)
    • A Shapiro-Wilk test is a quantifiable test with the null hypothesis: the data are normally distributed.  If p < 0.05, the data are NOT normally distributed.
  6. What is the p-value?
    The probability of obtaining a test statistic at least as extreme as the one that was actually observed, assuming that the null hypothesis is true.
  7. How is this image skewed?
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    The image is left skewed because there are outliers on the left.
  8. What is the difference between screening tests and diagnostics tests?
    • Screening involves classifying asymptomatic people as likely or unlikely to have a disease or condition. (ie, identifies high risk individuals from a healthy population)
    • Diagnostic tests are used to test individuals who are believed to be sick.
  9. Compare primary prevention, secondary prevention, and tertiary prevention.
    • Primary prevention: preventing a disease from occurring
    • Secondary prevention: Preventing symptoms after a disease has its biological onset.
    • Tertiary prevention: Treating symptoms to prevent death or other problems
  10. Compare validity and reliability
    • Validity: Asks if the test is measuring what it is supposed to.  Are the results correct?
    • Reliability: Do we get the same result over and over?
    • A test can be reliable but not valid (consistently gives the wrong results, etc)
  11. Compare internal validity and external validity.
    • Internal validity: Does your test measure what it is supposed to measure?
    • External validity: How well does the test generalize to the population at large?
  12. How do you calculate sensitivity
    • Sensitivity = true positives / (true positives + false negatives)
    • = TP / (TP + FN)
  13. How do you calculate specificity?
    • Specificity = true negatives / (true negatives + false negatives)
    • = TN / (TN + FN)
  14. What is the criterion of positivity?
    • The test value at which we assume a positive result for a test with a scale of result values. Ie, the cut off point.
    • The criterion of positivity affects sensitivity and specificity.
  15. When to optimize tests for specificity or sensitivity.
    • For fatal diseases with no treatment, you want to optimize specificity so that you don’t give someone false bad news (ie, that they have HIV when they don’t).
    • For treatable diseases, we want to optimize the test for sensitivity so that we can catch and treat the diseases.
  16. How do you calculate accuracy?
    Accuracy = (TP + TN)/ (TP + TN + FP + FN)
  17. How do you calculate the positive predictive value?
    • Positive predictive value = TP / (TP + FP)
    • This reflects the probability that a positive test reflects the underlying condition being tested for.
  18. How do you calculate the negative predictive value?
    • Negative predictive value: TN / (TN + FN)
    • A high NPV means that the test only rarely misclassifies a sick person as being healthy
  19. What is a nucleoside and what is a nucleotide?
    • Nucleoside: Nitrogenous base + sugar (eg, deoxyribose).
    • Nucleotide: Nitrogenous base + sugar + phosphate.
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  20. Differentiate between DNA and RNA
    • DNA has Deoxyribose, so the 2nd carbon (the first is the anomeric carbon) has an H instead of OH.
    • DNA is double stranded, providing a longer half life, RNA is single stranded with a shorter half life.
    • DNA: A-T, C-G. RNA: A-U, C-G.
    • Ribonucleotides can also function as second messengers (cAMP, cGMP), energy donors (ATP, GTP), and carriers of electrons for oxidation-reduction reactions (eg, Nicotinamide adenine dinucleotide, aka NAD+))
  21. What is the molecular structure of purines?
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  22. What is the molecular structure of pyrimidines?
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  23. What types of bonds are involved in DNA helices?
    • Phosphodiester bonds form between neighboring 3’ and 5’ hydroxyl groups to form the DNA backbone.
    • Hydrogen bonds between nitrogenous bases (A-T has 2 H bonds, C-G has 3 H bonds) keep the strands together.
    • Van der Waals forces stabilize the double helix structure.
  24. Describe the pathway to nucleotide synthesis
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  25. Describe the pathway through which nucleotides are synthesized from intermediates in the degradative pathway for nucleotides (ie, nucleotide salvage).
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