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Biostatistics > Final 1 > Flashcards

Final 1 Flashcards

1
Q

Choose the right statement.

The slope of the regression line cannot be more than one.

The slope of the regression line cannot be zero.

The slope of the regression line cannot be less than negative one.

The slope of the regression line can be any real number.

A

The slope of the regression line can be any real number.

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2
Q

What is the relation between the cumulative distribution and probability density functions of a random variable?

The probability density function is the derivative of the cumulative distribution function.

The cumulative distribution function and the probability density function cannot be given by each other.

The cumulative distribution function is the inverse of the probability density function.

The probability density function is the integral of the cumulative distribution function.

((Or cumulative is the integral of the probability density function.))

A
  • The probability density function is the derivative of the cumulative distribution function.
  • ((Or cumulative is the integral of the probability density function.))
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3
Q

We are studying the applicability of a diagnostic test. What is the name of the parameter given by the ratio of true positive and all positive tests?

positive predictive value

sensitivity

specificity

negative predictive value

A

positive predictive value

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4
Q

What is the number of degrees of freedom in case of a correlation t-test, if the sample size is 28? Its n-2 ( but you count them in pairs)

27

26

28

54

A

26

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5
Q

Pick the correct statement.

The condition of t-test for one sample is that the variable to be analyzed follows normal distribution.

T-test can only be applied for variables following standard normal distribution.

The condition of t-test for one sample is that the variable to be analyzed follows Student’s t distribution.

The condition of t-test for one sample is that the standard deviation is one.

A
  • The condition of t-test for one sample is that the variable to be analyzed follows normal distribution.
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6
Q

We would like to compare the efficacy of an original drug and a generic one. Choose the correct null hypothesis.

The efficacy of the generic drug is not significantly different from the original.

The efficacy of the generic drug is not identical to that of the original one.

The difference between the efficacy of the two drugs is not because of incidence.

Incidence has no role in the efficacy difference between the two drugs.

A
  • The efficacy of the generic drug is not significantly different from the original.
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7
Q

Select the correct statement.

  • The less the probability of occurrence of the signal, the less its information content.
  • There is no relation between the probability of occurrence of the signal and its information content.
  • The less the probability of occurrence of the signal, the more its information content.
  • The more the probability of occurrence of the signal, the more its information content.
A

The less the probability of occurrence of the signal, the more its information content.

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8
Q

A test for homogenity is to be conducted. Which method shall be used?

Student’s t-test for one sample.

Chi-square test.

Student’s t-test for two samples.

Mann–Whitney U-test

A
  • Chi-square test.
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9
Q

The sample p-value calculated during a Wilcoxon test is 0.353. The critical p-value is 5%. Choose the correct statement.

The difference between the medians is significant in 65% of all cases.

The null hypothesis is accepted, i.e. there is no significant difference between the values measured before and after the treatment.

There is no significant difference between the medians in 65% of all cases.

The null hypothesis is rejected, i.e. a significant difference can be assumed between the values measured before and after the treatment.

A
  • The null hypothesis is accepted, i.e. there is no significant difference between the values measured before and after the treatment.
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10
Q

We want to test with a t-test whether the 47 patients in the hematology ward have the same red cell count as the 47 patients in the contagious ward. What is the number of degrees of freedom?

46

48

92

24

A
  • 92
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11
Q

We are studying the applicability of a diagnostic test. What is the name of the parameter given by the ratio of true positive tests and all ill people?

prevalence

negative predictive value

sensitivity

specificity

A
  • sensitivity
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12
Q

We are studying a numerical, continuous variable in two groups having equal number of elements. Both groups show normal distribution, the variances can be considered equal. Can we use Mann–Whitney U-test in this case?

No, we cannot because non-parametric test can be used only for non-numerical data.

No, we cannot, we have to use t-test, since the conditions fulfill the requirements for t-test.

No, we cannot, in the described conditions we have to use Kruskal–Wallis-test.

Yes, we can because the sample fulfills the preconditions of the test.

A
  • No, we cannot, we have to use t-test, since the conditions fulfill the requirements for t-test.
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13
Q

What is the number of degrees of freedom in case of a chi square test for homogenity, if we study whether the distributon of male and female patients in our 8 hospitals is uniform?

7

14

6

1

A
  • 7
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14
Q

Which parameter is a central tendency?

Standard deviation.

Variance.

Square of the standard deviation.

Arithmetic mean.

A
  • Arithmetic mean.
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15
Q

The probability of occurrence of an event is 0.87. What is the probability that it does not occur?

  • 0.13
    0. 44
    0. 13

0

A
  • 0.13
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16
Q

Choose the right statement on type II error.

The null hypothesis is accepted, although it is false.

Gives the error of wrong decision.

The alternative hypothesis is accepted, although it is false.

Gives the error of the right decision.

A
  • The null hypothesis is accepted, although it is false.
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17
Q

In which case is the following equation valid: p(A + B) = p(A) + p(B).

If “A” and “B” are dependent events.

For any “A” and “B” events.

If “A” and “B” are independent events.

If “A” and “B” are mutually exclusive events.

A
  • If “A” and “B” are mutually exclusive events.
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18
Q

What is the right decision, if the calculated sample p-value is 0.022, and the critical p-value is 0.125?

  • The null hypothesis is accepted.
  • Neither the null nor the alternative hypothesis can be accepted.
  • The alternative hypothesis is rejected.
  • The null hypothesis is rejected.
A
  • The null hypothesis is rejected.
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19
Q

The pain killer effect of Aspirin and a new drug called “Novanopain” is compared. Choose the optimal test method.

  • Mann–Whitney U-test.
  • Two sample t-test, since we want to compare two independent groups.
  • Examining correlation between the two groups with t-test.
  • Simply compare the confidence intervals.
A
  • Mann–Whitney U-test.
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20
Q

Select the correct statement.

  • In a series of measurements, relative frequencies can always be summed without further conditions.
  • In a series of measurements, the sum of all conditional relative frequencies yields always 1.
  • In a series of measurements, frequencies can always be summed without further conditions.
  • In a series of measurements, conditional relative frequencies can always be summed without further conditions.
A

In a series of measurements, the sum of all conditional relative frequencies yields always 1.

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21
Q

What is the number of degrees of freedom in case of a correlation t-test, if the sample size is 14?

  • 26
  • 12
  • 14
  • 13
A
  • 12
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22
Q

The sample p-value calculated during a Wilcoxon test is 0.144. The critical p-value is 5%. Choose the correct statement.

  • The null hypothesis is rejected, i.e. a significant difference can be assumed between the values measured before and after the treatment.
  • There is no significant difference between the medians in 86% of all cases.
  • The difference between the medians is significant in 86% of all cases.
  • The null hypothesis is accepted, i.e. there is no significant difference between the values measured before and after the treatment.
A
  • The null hypothesis is accepted, i.e. there is no significant difference between the values measured before and after the treatment.
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23
Q

The probability of occurrence of an event is 0.96. What is the probability that it does not occur?

0.04

0

  • 0.04
    0. 48
A
  • 0.04
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24
Q

What is the right decision, if the calculated sample p-value is 0.036, and the critical p-value is 0.1?

The null hypothesis is rejected.

Neither the null nor the alternative hypothesis can be accepted.

The null hypothesis is accepted.

The alternative hypothesis is rejected.

A
  • The null hypothesis is rejected.
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25
Q

We are studying the applicability of a diagnostic test. What is the name of the parameter given by the ratio of true positive and all positive tests?

positive predictive value

negative predictive value

specificity

sensitivity

A
  • positive predictive value
26
Q

What is the number of degrees of freedom in case of a chi square test for homogenity, if we study whether the distributon of male and female patients in our 5 hospitals is uniform?

8

4

3

1

A
  • 4
27
Q

The expected value of a normally distributed variable can be found with 95% probability …

… in the following interval: mean ± two times the variance.

… in the following interval: mean ± two times the standard error.

… in the reference range.

… in the following interval: mean ± two times the standard deviation.

A
  • … in the following interval: mean ± two times the standard error.
28
Q

Choose the definition of frequency in statistics.

The frequency of an event is equal to the count of its occurrence in a series of observations.

The frequency of an event is equal to the count of its occurrence in the population.

The frequency of an event is equal to the count of observations.

The frequency of an event is equal to the count of its occurrence per unit time.

A
  • The frequency of an event is equal to the count of its occurrence in a series of observations.
29
Q

If the sample size goes to infinity …

… the mean goes to the average.

… the mode goes to the expected value.

… the standard deviation goes to zero.

… the relative frequency of an event goes to its probability.

A
  • … the relative frequency of an event goes to its probability.
30
Q

We tossed a fair coin 4 times and the outcome was always heads. What is the probability that the outcome of the 5th toss is heads?

  • Not enough data to tell.
  • It is 50%.
  • It is (1/2) ÷ 5 = 1/10.
  • It is (1/2)^5 = 1/32.
A
  • It is 50%.
31
Q

Which parameter is a central tendency (“middle value”)?

Variance.

Square of the standard deviation.

Standard deviation.

Arithmetic mean.

A
  • Arithmetic mean.
32
Q

What is the reason of the fact that most physiological variables are characterized by normal distribution?

  • They are all related to each other so they must have the same (or at least similar) distribution.
  • In fact, most of them does not follow normal distribution, and we rather deal with those few which do.
  • They are actually transformed so that they would follow normal distribution which makes them easier to be dealt with.
  • They influenced by many independent events, and this, according to the central limit theorem, yields normal distribution.
A
  • They influenced by many independent events, and this, according to the central limit theorem, yields normal distribution.
33
Q

What type of function is the following: f(x) = ex.

  • Reciprocal function.
  • Exponential function.
  • Linear function.
  • Power function.
A
  • Exponential function.
34
Q

The probability of occurrence of vascular stenosis among smokers is 0,31. The probability of being a smoker in a given population is 0,34. What is the probability in this population that someone is a smoker with vascular stenosis?

  • Data is too few to answer.
  • 0.912
  • ~1
  • 0.105
A
  • 0.105
35
Q

“A” and “B” are mutually exclusive events. The probability of event “A” is 0,29. What is the probability of event ‘B’?

  • Maximum 0,71.
  • Exactly 0,71.
  • Minimum 0,29.
  • Not more than -0,29.
A
  • Maximum 0,71.
36
Q

The correlation coefficient is close to one if …

  • … the relationship between the variables is linear with positive increment.
  • … the relationship between the variables is linear.
  • … the relationship between the variables is not significant.
  • … the relationship between the varialbes is function-like.
A
  • … the relationship between the variables is linear with positive increment.
37
Q

We are executing a two-tailed t-test. Choose the possible outcome.

  • t = 0 and p = 1.
  • p = 0 and t = 1.
  • t = 0 and p = 0.
  • t = 100 and p = 1.
A
  • t = 0 and p = 1.
38
Q

The sample p-value calculated during a Wilcoxon test is 0,283. The significance level is 5%. Choose the correct statement.

  • The difference between the medians is significant in 71,70% of all cases.
  • The null hypothesis is rejected, i.e. a significant difference can be assumed between the values measured before and after the treatment.
  • The null hypothesis is accepted, i.e. there is no significant difference between the values measured before and after the treatment.
  • There is no significant difference between the medians in 71,70% of all cases.
A
  • The null hypothesis is accepted, i.e. there is no significant difference between the values measured before and after the treatment.
39
Q

What does the term “tied rank” stand for in statistics?

  • Ranks that are assigned to data in a two-sample t-test for data pairs.
  • Ranks not exchangeable between samples.
  • Ranks not exchangeable within a sample.
  • Identical ranks that are assigned to values of equal magnitude.
A
  • Identical ranks that are assigned to values of equal magnitude.
40
Q

When is ANOVA applicable?

  • If more than half of the samples to be compared are normally distributed.
  • If the variance of the samples is equal and all samples are normally distributed.
  • If the samples to be compared are independent and normally distributed.
  • When it yields less alpha and beta error than a series of paired t-tests.
A
  • If the samples to be compared are independent and normally distributed.
41
Q

Choose the right statement. The y axis intercept of the regression line …

  • … cannot be more than one.
  • … cannot be less than negative one.
  • … can be any real number.
  • … cannot be zero.
A
  • … can be any real number.
42
Q

What is the number of degrees of freedom in case of a correlation t-test, if the sample size is 22?

  • 21
  • 20
  • 22
  • 42
A
  • 20
43
Q

The calculated sample p-value in a two sample t-test is 1.007; the significance level is 5%. Choose the correct conclusion.

  • Because p < 5, the null hypothesis is rejected, i.e. there is no significant difference.
  • Because p > 5%, the treatment is efficacious.
  • We cannot make a decision, a calculation error must have occured.
  • The sample p-value is great enough to accept the null hypothesis.
A
  • The sample p-value is great enough to accept the null hypothesis.
44
Q

Choose the right statement. The sampling is good if …

  • … its size is around the square root of the size of the population.
  • … the combined magnitude of type I and type II errors does not exceed 5%.
  • … the sample contains roughly 95% of the possible values.
  • … the relative frequency distribution of the sample is not significantly different form the probability density function of the population.
A
  • … the relative frequency distribution of the sample is not significantly different form the probability density function of the population.
45
Q

Choose the right statement on information content.

  • Its unit is selby.
  • The information content of a “message” consisting of a single sign is equal to log2(1).
  • It has no unit.
  • The less frequent event has less information content.
A
  • The information content of a “message” consisting of a single sign is equal to log2(1).
46
Q

In which case should one reject the null hypothesis?

  • If the absolute value of the statistical parameter calculated from the sample is greater than 5%.
  • If the p-value calculated from the sample is greater than the critical p-value.
  • If the p-value calculated from the sample is greater than 5%.
  • If the absolute value of the statistical parameter calculated form the sample is greater than the absolute value of the critical statistical parameter.
A
  • If the absolute value of the statistical parameter calculated form the sample is greater than the absolute value of the critical statistical parameter.
47
Q

Which one of the following is an example of statistical inference?

  • Calculating the sample t-value.
  • Rejecting the null hypothesis as a result of hypothesis testing.
  • Calculating the second central moment of the sample.
  • Calculating the second moment of the sample.
A
  • Rejecting the null hypothesis as a result of hypothesis testing.
48
Q

The probability of occurrence of vascular stenosis among smokers is 0.26. The probability of being a smoker in a given population is 0.34. What is the probability in this population that someone is a smoker with vascular stenosis?

  • 0.765
  • ~1
  • Data is too few to answer.
  • 0.088
A

0.088

49
Q

Choose the right statement. The y axis intercept of the regression line …

  • … cannot be zero.
  • … cannot be more than one.
  • … cannot be less than negative one.
  • … can be any real number.
A
  • … can be any real number.
50
Q

We would like to examine the relationship between smoking and performance at school. Choose the correct null hypothesis.

There is no relationship.

Smokers perform significantly worse although no exact realtionship is supposed.

The difference between the performance of smokers and non-smokers is not significant.

Smokers perform significantly worse and an exact realtionship is supposed.

A

The difference between the performance of smokers and non-smokers is not significant.

51
Q

The following statements are about the reference range. Pick the true one.

The measeured units falling out of the reference range come from ill people.

There is roughly 2.5% probability that a measured value of a normally distributed variable falls below the reference range.

The reference range contains approx. 65% of the elements of the population.

The refernece range is used for both normally and non-normally distributed variables.

A

There is roughly 2.5% probability that a measured value of a normally distributed variable falls below the reference range.

52
Q

We want to test with a t-test whether the 34 patients in the gynecology ward have the same white cell count as the 34 patients in the psychiatry ward. What is the number of degrees of freedom?

17

66

35

33

A

66

53
Q

What does the term “tied rank” (or “linked rank”) stand for in statistics?

Ranks not exchangeable between samples.

Identical ranks that are assigned to values of equal magnitude.

Ranks not exchangeable within a sample.

Ranks that are assigned to data in a two-sample t-test for data pairs.

A

Identical ranks that are assigned to values of equal magnitude.

54
Q

In meteorology, the intensity of UV-B radiation is classiefied as follows: weak, moderate, strong, very strong, extreme. What is the type of this data?

Exponential.

Categorial.

Discrete numerical.

Not enough information to decide.

A

Categorial.

55
Q

A test for fit for normal distribution is executed. The result is sample p-value = 0.756. Choose the right decision.

  • p > 0.05, so the null hypothesis is rejected, i.e. the sample does not deviate significantly from normal distribution.
  • The null hypothesis is rejected, i.e. the sample distribution is not normal.
  • We accept the null hypothesis, i.e. the sample in question fits for normal distribution.
  • Because p > 0.05, we accept the null hypothesis, i.e. it is not normally distibuted.
A

We accept the null hypothesis, i.e. the sample in question fits for normal distribution.

56
Q

Choose the definition of frequency in statistics.

The frequency of an event is equal to the count of its occurrence in a series of observations.

The frequency of an event is equal to the count of its occurrence per unit time.

The frequency of an event is equal to the count of its occurrence in the population.

The frequency of an event is equal to the count of observations.

A

The frequency of an event is equal to the count of its occurrence in the population.

57
Q

Standard normal distribution is identical to …

  • … Student’s t-distribution with infinity degrees of freedom.
  • … uniform distribution.
  • … the Gaussian distribution.
  • … lognormal distribution.
A

… the Gaussian distribution.

58
Q

Choose the correct statement.

The fourth central moment describes the extent how much heavier one tail of a probability density function is relative to the other.

The third central moment is related to skewness.

The first central moment is one.

The second central moment is standard deviation.

A

The third central moment is related to skewness.

59
Q

What is the power gain level. if the ratio of the output and input power is 1?

10 dB

1 dB

20 dB

0 dB

A

0 dB

60
Q

Which of the following is a measure of spread?

  • Mean.
  • Mode.
  • Median.
  • Range.
A
  • Range
61
Q

We are executing a two-tailed t-test. Choose the possible outcome.

p = 0 and t = 1.

t = 0 and p = 1.

t = 100 and p = 1.

t = 0 and p = 0.

A

t = 0 and p = 1.

62
Q

The probability of event “A” is 0.57. What is the maximum possible probability of event ‘B’ if events ‘A’ and ‘B’ cannot happen at once?

  • Exactly -0.57.
  • Precisely 43%.
  • It can be anywhere between 0 and 1.
  • It can be anywhere between 0 and 0.43.
A
  • It can be anywhere between 0 and 0.43.

Biostatistics (5 decks)

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