some relevant questions epi

2

A clinical trial of a new drop for dry eye randomized 100 people into two groups divided equally between treatment and control groups. At the end of the study, the number of people with relief from symptoms was 33 for the new drop and 11 for the placebo. For these results, the Number Needed to Treat (NNT):

3.57

A clinical trial of a new steroid drop for anterior uveitis (inflammation in the eye) randomized 100 people, 50 in the treatment group and 50 in the control group. At the end of the study, the number of people with serious side effects like glaucoma and cataracts was 20 for the new drop and 6 for the placebo. For these results, the Number Needed to Harm (NNH), rounded to the nearest integer.

obtaining treatment groups with comparable baselines (age, sex, SES, height, weight, IOP, etc.)

A clinical trial randomizes patients into treated and control groups with the goal of:

Vitamin D

A gene arose ~8000 years ago that allowed humans to have low skin pigmentation. This allowed them to flourish in European areas with low levels of ultraviolet rays, which are used in the production of what nutrient?

increase your power (because it reduces the potential error in measuring the effect)

A new autorefractor is developed with a higher degree of precision which allows you to measure refractive error at 0.01 Diopters instead of 0.25. What effect does that have on the power of your study to measure myopia progression? (increase/decrease)

4.3

A new diagnostic test for acanthamoeba keratitis has be found to have a sensitivity of 100% and specificity of 86%. The prevalence of acanthamoeba keratitis in your clinic population has been 9 out of every 10,000 people with corneal damage. If you used a test with every one of your patients who had corneal damage, what do you expect the positive predictive value to be?

85.25

A new diagnostic test for dry eye has been found to have a sensitivity of 73% and specificity of 84%. The prevalence of dry eye in your clinic population has been 35 out of every 100 over the age of 50. If you use this test with every one of your patents over 50, what do you expect the negative predictive value to be?

11 (1/%drug-%placebo)

A new eye drop called Clarkprost has become available to lower the pressures for glaucoma. From research, you know that the medication will reduce pressures by 20%, resulting in absolute risk of visual field progression 13% for the patients on the medicine. The risk of untreated eyes developing visual field progression is 22%. What is the NNT?

0.70 (54-16)/ (54)

A new eye drop called Clarkprost has become available to lower the pressures for glaucoma. From research, you know that the medication will reduce pressures by 20%, resulting in an absolute risk of visual field progression 16% for the patients on the medicine. The risk of untreated eyes developing visual field progression is 54%. Calculate the relative risk reduction.

27.9

A new test for COVID-19 has a sensitivity of 94% and a specificity of 93%. Your clinic estimates that 2.8% of your patients have an active COVID-19 infection. If you test every patient for COVD-19, what percentage of the time do you expect a positive test result to be correct? Put your answer in percentage.

0.36

A new test has been developed to detect Primary Open-Angle Glaucoma (POAG). The test was administered to patients and compared to the gold standard of POAG diagnosis of IOP, ONH and Visual fields. Calculate Specificity.

0.71

A new test has been developed to detect Primary Open-Angle Glaucoma (POAG). The test was administered to patients and compared to the gold standard of POAG diagnosis of IOP, ONH and Visual fields. The confusion matrix is provided above. Calculate the Negative Predictive Value of the new test.

0.72

A new test has been developed to detect Primary Open-Angle Glaucoma (POAG). The test was administered to patients and compared to the gold standard of POAG diagnosis of IOP, ONH and Visual fields. The confusion matrix is provided above. Calculate the Negative Predictive Value of the new test. Answers should be in decimal places, as an example 0.30.

0.52

A new test has been developed to detect Primary Open-Angle Glaucoma (POAG). The test was administered to patients and compared to the gold standard of POAG diagnosis of IOP, ONH and Visual fields. The confusion matrix is provided above. Calculate the positive predictive value or precision of the new test.

0.5

A new test has been developed to detect diabetes. The test was administered to patients and compared to the gold standard of diabetes diagnosis of hemoglobin A1C. The confusion matrix is provided above. Calculate the prevalence of diabetes from this study.

39% (risk untreated-risk treated)

A patient and their mom come in wanting to be fit in MiSight to reduce the patient's myopia progression. From research, you know that reducing their myopia by 50% will lead to an Absolute Risk for retinal detachment and myopic choroidal neovascularization to 2% for treated patients. The risk untreated is 41%. Calculate Absolute Risk Reduction.

2

A patient and their mom come in wanting to be fit in MiSight to reduce the patient's myopia progression. From research, you know that reducing their myopia by 50% will lead to an Absolute Risk for retinal detachment and myopic choroidal neovascularization to 2% for treated patients. The risk untreated is 46%. Calculate NNT.

1 in 1,000

A power calculation for a study decided to use a significance criteria with a p-value of 0.001. What is the probability that this study will find a significant effect by random chance?

The difference found may be the result of sampling variation

A study of 10 cases of a disease and 20 controls determined that the difference found with respect to a possible etiologic factor was not statistically significant. Which of the following may be concluded?

The significance criteria should be lowered to decrease the risk of Type I errors

A typical significance criteria, we assume results with a P-value below 0.05 to be statistically significant. In a study measuring cataract development, they are looking at the effect of 20 drugs on the development of early cataracts. What does this mean for the significance criteria?

the Kappa value shows that within-observer agreement was poor

An abstract states"The correlation between test and retest scores on the SSD-OCT was highly significant (Pearson's r = 0.25, p < 0.00001. Between-observer agreement (Kappa = 0.32) was just as good as test-retest agreement (Kappa = 0.31)." What can be concluded based on the kappa values?

40% (80/200=.04)

An optometrist devised a short screening test for myopia. An independent double-blind study was made comparing it with the gold standard for diagnosis of myopia among 200 optometric patients. Among the 80 found to be myopic via the gold standard, 65 were positive for the new test. Among 120 that were not myopic with the gold standard, 30 patients were found to be positive for the test. What is the prevalence of myopia in this study?

0.81

An optometrist devised a short screening test for myopia. An independent double-blind study was made comparing it with the gold standard for diagnosis of myopia among 200 optometric patients. Among the 80 found to be myopic via the gold standard, 65 were positive for the new test. Among 120 that were not myopic with the gold standard, 30 patients were found to be positive for the test. What is the sensitivity in this study?

76%

As a 3rd-year student you are assigned to assist in the ocular disease clinic by assessing the presence, absence and/or severity of ocular pain (using a scale of 0 for no pain to 3 for severe pain) in patients who present with a complaint of recent blurring of vision. Following your assessment, your clinical consultant makes an independent assessment on the same patients. Based on the following assessments, what is the reliability of your findings compared to those of your consultant on the assessment of pain in your patients? PICTURE

Infectious keratitis is becoming more acute (incidence same, prevalence decreases)

Based on the data presented (see picture) which of the following conclusions is most appropriate?

e. all of these places

Caucasian people are the majority of the population in which of the following? a. northern europe b. northern africa c. india d. pakistan e. all of these places

60 per 100,000 per year

Clark's Iridocyclitis is a rare fictional disease occurring during the summer semester from May through June and has a prevalence of 10 per 100,000. What is the incidence rate per year?

to develop age norms for clinical test

Clinically, why is linear regression is useful for optometrists?

increase, decrease

Current standard of diagnosis for diabetes is a Hemoglobin A1C measurement, with above 6.5 being considered diabetic. What would happen to the sensitivity and specificity if the cutoff was lowered to above 5.5? the sensitivity would (increase/decrease), the specificity would (increase/decrease)

decrease, increase

Current standard of diagnosis for diabetes is a Hemoglobin A1C measurement, with above 6.5 being considered diabetic. What would happen to the sensitivity and specificity if the cutoff was raised to above 7.5? the sensitivity would (increase/decrease), the specificity would (increase/decrease)

Trachoma (bc it can be prevented by sanitation so it is before the sanitary stage)

Diseases wax and wane over time with some diseases being more prevalent in the later stages than in the early stages of a society's epidemiologic transition. Which of the following eye diseases most likely would be found in societies that are less developed (i.e., in the early stages of epidemiologic transition)?

Infectious keratitis is becoming less infectious (incidence decreased, prevalence same, so less are being diagnosed each year)

Following data shows an ongoing study of infectious keratitis. What is the most accurate conclusion?

The independent variable was not used to select subjects

For linear regression using clinical data, the validity of the regression line is reduced by which factor?

1. Positive Correlation 2. It shows the two eyes are not independent from each other 3. About 80% of the left eye's refractive error can be explained by the right eye's refractive error

For the figure, what can be said about it? PICTURE

Instrument Skew

Here are two instruments comparing IOP measurements using different tonometers. What is this an example of?

Folate

Humans developed pigmented skin to protect ________ from being destroyed by ultraviolet rays

The fact that doctors did not wash their hands (gross)

Ignaz Semmelweis's experiment in 1847 found that childbed (puerperal) fever was primarily caused by?

Prevalence Rate

In Indiana in 2020, 6,700 people have histoplasmosis. This measure is best categorized as?

Double-Masked

In a randomized clinical trial comparing two different contact lens solutions, the patients were given a blank white bottle with a code on it. The clinicians who were doing the evaluations were unaware of the meaning of the code. This design is known as a ______ study.

there is no significant risk difference between cell phones and radio sets

In a study of increased risk of eye cancer and cell phone usage, the authors found the Odds Ratio (OR) for radio sets to be 3.0, with a 95% confidence interval (CI) of 1.4 to 6.3. The OR for cell phones was 4.2, 95% CI of 1.2 to 14.5. You could conclude that:

Impact will be higher for the later event

In survival analysis, what is the difference in the statistical impact of an "event" early in the study versus an event late in the study?

Incidence Rate

In the United States, 300 per 10,000 ten-year-old children developed myopia in 2020. How would you describe this measurement?

0

Look at the Bland-Altman plot above. What is the mean difference between the two measures?

They are inversely related and statistically significant

Look at the figures below. This is a study looking a changes in refractive error in infants and which ocular components are associated with it. What does regression in figure A tell you about the correlation between axial length and refractive error changes?

There is no significant association

Look at the figures below. This is a study looking at a CHANGE in refractive error in infants and which ocular components are associated with it. What does regression in figure B tell you about the correlation between lens power and refractive error changes?

About 15% of the variability is explained by axial length and refractive error changes

Look at the figures below. This is a study looking at changes in refractive error in infants and which ocular components are associated with it. What does R squared mean in figure A?

Bland-Altman

Precise IOP is important in glaucoma practice. Various instruments are available today to accurately measure IOP. [...] To assess the agreement between NCT, RBT, GAT, and DCT in measuring IOP, 499 eyes of 250 patients were evaluated during 24 months and measurement of IOP was done. The mean IOP of NCT, RBT, GAT, and DCT was 15.9 +- 5.8, 15.9 +-4.9, 15.9 +- 4.9, 16.0 +- 4.7 mmHg. The limits were found [...], Positive and strong correlation was found between newer tonometers and GAT, but the limit of agreement was clinically unacceptable. The use of a single tonometer should be practiced at a glaucoma clinic for a patient at each follow-up. Which type of statistical analysis should be used for this study?

ALL groups

Prior to the Belmont Report, researchers performed invasive experiments on OPTIONS

Prospective Study

Read the following study and determine study design. see picture.

d. a confounder is present

Suppose that a retrospective study was conducted on the risk of crashing a computer while under the influence of alcohol. The study looked at the history of computer crashes for 100 college students and 100 senior citizens, and asked about alcohol use. The crude Odds Ratio (OR) was determined to be 2.0, the age-specific associations were OR = 1.0 for the college students and OR = 1.0 for the senior citizens. You could conclude that: a. the true risk to the population is reflected in the crude association b. a modifier of risk is present c. the old are at significantly greater risk d. a confounder is present e. significant risk is present on both levels

False (case-control studies do not follow people)

T/F: Controls are needed in a case-control study so that they may be followed to determine whether they develop the disease in question.

True

T/F: human races are social constructs with NO genetic basis

False (value depends on study design)

T/F: the P-value for a study is the same for all studies

The treatment group progressed less than the treatment group with similar drop out rates, however, all the effect was in the first year or two, and then both groups progressed similarly

The above plot is a survival plot of a contact lens being studied to stop the progression of myopia compared to spectacle lens control group. The p-value between groups was 0.001. Based upon the above, what can be said about the results? PICTURE

The treatment lens appears to slow the progression of myopia but there is a high level of dropout in that group making the results questionable

The above plot is a survival plot of a contact lens being studied to stop the progression of myopia compared to spectacle lens control group. The p-value between groups was 0.001. Based upon the above, what can be said about the results? PICTURE

Sensitivity of 0.90 and specificity of 0.70

This is a ROC curve for the ability of HbA1c to predict diabetes. HbA1c measures the percentage of glucose attached to hemoglobin. Higher levels of HbA1c are correlated with diabetes. What is the specificity and sensitivity using a 5.8 HbA1c threshold?

The Cirrus measured the macula 50 microns thicker than the Stratus

This plot compared the macular thickness of two different optical coherence tomographers (OCT) (Cirrus vs Stratus). What does this show?

8

To investigate the association between dry eye syndrome (DES) and heavy computer use, investigators conducted a case-control study with 100 cases (100 office workers with DES) and 100 controls (100 office workers without DES). Among workers with DES, 56 gave a history of heavy computer use. Among workers without DES, 14 gave a history of heavy computer use. For this study, the odds ratio for effect of heavy computer use is:

Disease B (because prevalence accumulates over time)

Two diseases both have an incidence of 3%. Disease A resolves over the course of 2 weeks and disease B is cured over 2 years. Which has the higher prevalence?

1 in 20 times

What does a significance criteria of 0.05 mean? the result would have happened ____ in ____ times.

+/- 10 microns

What is the 95% confidence interval for this figure?

Incidence Rate

What is the best measure to estimate how fast new cases of histoplasmosis develop in Indiana (a fungal infection of the retina common in the region)?

0.86

What is the exact agreement for the two graders below for measuring the presence or absence of retinopathy? Answers should be recorded to 2 decimal places, as in 0.95. PICTURE

Instrument Bias

What type of bias is this Bland-Altman plot illustrating?

the cause of death would be affected by race

What was the hypothesis that the Tuskegee Syphilis Study evaluated?

a. number of study sites

Which of the following does NOT affect the power of a study? a. number of study sites b. sample size c. precision of instrument being used to collect data d. significance criteria (p value used)

His use of ecologic, descriptive, observational, & experimental designs in one investigation

Which of the following makes John Snow's work on cholera one of the classical milestones in the epidemiological investigation?

prospective cohort (only this can give incidence)

Which of the following study designs would be the most appropriate for a study designed to determine the incidence of macular degeneration in a population of people age 50 years and over?

Respect

Which of the three principles of the Belmont report is most directly related to the necessity of informed consent?

can disclose unexpected risk factors

Which one is not an advantage of a clinical trial study?

e. estimate Incidence of a disease(only a cohort study can do this)

Which one of these goals cannot be met with a cross-sectional study? estimate..... a. specificity of test b. prevalence of a disease c. risk associated with a symptom d. sensitivity of a test e. incidence of a disease

C. can disclose unexpected risk factors (Because cohort studies are prospective and do not test a hypothesis, they can uncover unexpected factors)

Which one of these is not a disadvantage of a cohort study? a. inefficient for a rare dz b. Investigator attrition can affect variability in clinical evaluations c. can disclose unexpected risk factors d. subject attrition can affect representativeness of sample

0.6

You and a classmate measure intraocular pressures using Goldmann tonometry getting the results below. What is your agreement within limits of +/-1 mmHg? PICTURE

John Snow

_____ _____ is considered the father of epidemiology

type 1

______ error is when a study reaches statistical significance when there is NO actual difference between the two groups

NNH (number needed to harm)

______ is the number need to be treated before a bad outcome is seen (side effects)

type 2

_______ error is a study that does NOT reach statistical significance when there IS an actual difference between the two groups

prevalence

________ is the measure of the number of individuals with a disease at a given time

specificity

________ is the proportion of patients without the disease correctly identified as not having the disease

endemic

_________ means the disease is habitually present in that human population

sensitivity

__________ is the proportion of patients with the disease that are correctly identified to have the disease

incidence

_____________ is a measure of new patients developing a disease at a given time

independent

for linear regression, the ________ variable is a measurement used by the experimenter to select subjects for the study in order to have a uniform distribution

No conclusion can be made due to lack of report on effect size

given the abstract, what is your clinical take-home message?

Has come as far north in the US as the US-Canadian border

how far north has malaria come into the US?

larger (i.e. a drug that lowers IOP by 10 mmhg would have a larger magnitude of effect, and by extension better power, than a drug that only lowers IOP by 2 mmhg.)

the (larger/smaller) the magnitude, the better the power

NNT (number needed to treat)

the __________ is the number need to be treated in order for one patient to benefit the treatment

stronger (A study needs to be large enough to test the hypothesis, but kept to a minimum size needed to keep study costs down)

the larger the number of study participants the (stronger/weaker) the power of the study.