5 - community medicine mcqs - 31 to 40

Question 31 : Advantages of random sampling for studying the general human population include:

A. it can be applied to any population.
B. likely errors can be estimated.--------------------------- *
C. estimates obtained are not biased---------------------. * * Right
D. it is easy to do.
E. the sample can be referred to a known population.------------- * * Right

Question 32 : In a case-control study to investigate oral contraception and breast cancer:

A. cases would be women with breast cancer. *
B. controls would be given oral contraception.
C. cases would be given oral contraception.
D. women with breast cancer would be randomly allocated to be cases or controls.
E. controls would be observed for several years to see how many developed breast cancer.

Question 33 : In a case-control study, patients with lung cancer had a highly significantly lower cholesterol level than did controls. This provides strong evidence that:

A. low cholesterol causes lung cancer.
B. there is evidence for a relationship between low cholesterol and lung cancer in the sampled population. * * Right
C. low cholesterol is not related to lung cancer.
D. low cholesterol and lung cancer always go together.
E. low cholesterol is a risk factor for the development of lung cancer.

Question 34 : The paired t test is:

A. impractical for large samples.
B. equivalent to a chi-squared test.
C. suitable for very small samples.--------------------------------------- * * Right
D. used for independent samples.
E. requires the assumption that differences between paired observations follow a Normal Distribution. *

Question 35 : For a t test for two independent samples to be valid:

A. the numbers of observations must be approximately the same in the two groups.
B. the standard deviations of observations must be approximately the same in the two groups.---------------------- *
C. the means must be approximately the same in the two groups.
D. the observations must be from distributions which are approximately Normal.--------------------------------- * * Right
E. the sizes of samples the must be small.

Question 36 : A simple linear regression equation:

A. always describes a line which goes through the origin.
B. always describes a line with zero slope.
C. is not affected by changes in the units in which variables are measured.
D. describes a line which goes through the point defined by the means of the two variables. * * Right
E. is affected by the choice of dependent variable. ----------------------------------- *

Question 37 : The product-moment correlation coefficient between two variables, r:

A. must lie between -1 and +1 inclusive.------------------------------ *
B. can only have a valid significance test carried out when one variable follows a Normal Distribution.---------------- * * Right
C. is expected to be zero when there is no relationship between the variables.
D. depends on which of the two variables is chosen to be the dependent variable.
E. measures the magnitude of the change in one variable associated with a change in the other.

Question 38 : The standard chi-squared test for a 2x2 contingency table is not valid unless:

A. all the expected frequencies are greater than five.----------------------- *
B. both variables are continuous.
C. at least one variable is from a Normal Distribution.
D. all the observed frequencies are greater than five.
E. the sample size is at least 100.

Question 39 : To analyse the relationship between blood pressure and height in a sample of students, we could use:

A. paired t test
B. correlation coefficient--------------------------- *
C. chi-squared test
D. regression-------------------------- *
E. two sample t test

Question 40 : In a case-control study, 101 stroke patients were compared with 137 healthy controls. Among the results were: Cigarette smoking by stroke patients and healthy controls - Ever smoked? Cases: 71 yes, 30 never, 101 total; Controls: 36 yes, 101 never, 137 total; Chi-squared = 45.5, 1 degree of freedom, P less than 0.0001, Odds ratio = 6.6 (95% confidence interval = 3.8 to 11.8)

A. These data would be unlikely if smoking and stroke were unrelated. * * Right
B. It is estimated that the relative risk of stroke for ever-smokers compared to never-smokers is 6.6. * * Right
C. In the population from which cases and controls come, the odds ratio is estimated to lie between 3.8 and 11.8.----------------- Right *
D. We can conclude that smoking causes stroke.
E. There is good evidence that smokers have an increased risk of stroke. * *
Right

4 - biostatistics notes

BIOSTATISTICS NOTES

POPULATION: Universe of all units being studied.
If we want to study lung cancer among Indians, then the study population will be all Indians.
If we want to study lung cancer among Indian women, then the population will be all
Indian women.

SAMPLE: Subset of the population
RANDOM SAMPLE: Each member of the population has an EQUAL CHANCE of being chosen for the sample

SAMPLING METHODS (#5 is nonrandom)
#1 Simple Random Sample
#2 Systematic Sample
Example:
Rank 100 people by age
Beginning with the 5th person, choose every tenth
i.e. Choose the 5th,15th,25th ... 85th,95th persons

#3 Stratified Sample: Composition of the sample reflects composition of the population
Indian Population
Bengalis 60%
Punjabis 25%
Kashmiris 10%
Others 5%
Stratified Sample of 1000 Indians
Bengalis 600 (60%)
Punjabis 250 (25%)
Kashmiris 100 (10%)
Others 50 (5%)

#4 Cluster Sample (used for immunization studies)
ü Divide population into groups
ü Random sample of groups is chosen
ü Count every unit in each and every group selected
Example:
Divide entire city into "city blocks"
Random sample of blocks is chosen
Count every person in each city block selected

#5 Nonrandom/Convenience Sample
Example:
Interview people in a shopping mall. This is nonrandom because not everyone in the population goes shopping at the mall. People who are wheelchair-bound are less likely to visit the mall. This is also the case with people who have problems walking. Also, the mall may be too far away for those who don't have cars. If the interview is done during a weekday, people who work are unlikely to be at the mall (housewives and retirees are more likely to be interviewed on weekdays.

VALIDITY: You are actually measuring what you want to measure. Example: if IQ really measures intelligence, then IQ is high in validity. If it does not actually measure intelligence, then it is low in validity.

RELIABILITY: Refers to stability of measurement. Example: A research instrument is high in reliability if it gives consistent readings when it is used on the same subject even if the subject is measured at different times. Example of a "research instrument" is a survey questionnaire.

MEASURES OF CENTRAL TENDENCY (used to summarise a dataset)
1. Arithmetic Mean - affected by extreme values
2. Median
3. Mode

MEASURES OF DISPERSION (used to determine how spread out a dataset is)
1. Range - difference between highest and lowest values
2. Variance
3. Standard Deviation - the higher the Standard Deviation, the more spread out
the data. The Standard Deviation is the square root of the Variance.

THE STANDARD DEVIATION IS A VERY IMPORTANT MEASURE - Under a Standardised Normal Curve,

68.3% of the data are found +1 or -1 standard deviation from the mean
95.5% of the data are found +2 or -2 standard deviations from the mean
99.7% are found +3 or -3 standard deviations from the mean

LEVEL OF MEASUREMENT OF DATA
1. Nominal data: qualitative, categorical data. Example: ethnicity, SEX, religion.
2. Ordinal data: Rank-ordered data. Data are grouped from low to high. But we cannot say how much lower or how much higher. Example: "low anxiety", "moderate anxiety" and "high anxiety".
3. Interval data: quantitative data. There is fixed equal interval between numbers e.g.
the difference between 10 km and 15 km is the same as the distance between 30 km
and 35 km. Examples of interval data: height, weight, temperature measured using
the Celsius scale.
4. Ratio level data: Similar to Interval Data but in addition, it has an absolute zero e.g. income, temperature measured using the Kelvin scale.
NOTE: For Ratio Data, we can use ratio level, interval level, ordinal level and nominal level statistical tests.
For Interval Data, we can use interval level, ordinal level and nominal level tests.
For Ordinal Data, we can use ordinal level and nominal level tests.
But for Nominal Data, we can only use nominal level statistical tests.


INFERENTIAL STATISTICS/STATISTICAL INFERENCE
If we are doing research on a large population, we need not study each and every individual in the population. All we need to do is choose a sample (RANDOM and REPRESENTATIVE) from the population. We can use our findings from the sample to infer (draw conclusions) about the population.
Research Hypothesis/Alternative Hypothesis: the hypothesis we wish to test. Also
called H-one and written as H1
Null Hypothesis: opposite of the Research Hypothesis. Also called H-nought and
written as H0.
Examples:
Research Hypothesis - there is a statistically significant association between Smoking and Cancer
Null Hypothesis - there is no statistically significant association between Smoking and Cancer. Any association seen is due to chance

Research Hypothesis - there is a statistically significant difference between the two population means
Null Hypothesis - there is no statistically significant difference between the two population means. Any difference seen is due to chance

Significance Level/Confidence Level (denoted by α)
Usually set at 0.05 or 0.01
An α of 0.05 means we wish to test the statement "the probability of what we see occuring by chance is 5% or less” i.e. p Y
Example: We test to see if X <>
Standardised Normal Distribution: See description under "Standard Deviation"
In a normal distribution, the mean, median and mode are equal.
The curve is bell-shaped and symmetrical
The standardised normal distribution curve has a mean of zero and a standard deviation of 1.
Degree of freedom: the degree of freedom depends on the sample size or number of categories. The critical value of a statistical test changes with changes in the degree of freedom.

COMMON STATISTICAL TESTS
1. Chi-square test of goodness-of-fit,
ü single sample
ü (NOMINAL DATA - like religion)
ü Degree of freedom is n-1 (where n = number of categories)

2. Chi-square test of independence
ü (NOMINAL DATA).
ü Degree of freedom is (r-1) X (c-1) where r = number of rows and c = number of columns in a contingency table.
ü To test if there is a statistically significant association between two variables (between ethnicity and religion)

3. t-test for two independent samples
(INTERVAL DATA – like height and weight).
Degree of freedom = (n1-1) + (n2-1)
To test if there is a statistically significant difference between the two population means from the two samples.

4. t-test for two matched samples
(INTERVAL DATA).
Degree of freedom is n-1 where n = the number of pairs
To test if there is a statistically significant difference between the two population means from the two matched samples.

5. If there are more than two samples, we use the ANOVA test (Analysis of Variance) or F-test

NOTE: IF THERE ARE MORE THAN TWO SAMPLES, IT IS INCORRECT TO USE THE T-TEST TO MAKE PAIRWISE COMPARISONS
Example: if there are 3 samples, it is incorrect to compare mean #1 with mean
#2, mean #1 with mean #3, mean #2 with mean #3. The ANOVA test should be done on
the three means instead.

CHOOSING A TEST
1. What is the level of measurement? Nominal, ordinal or interval?
2. How many samples? One, two or more?
3. If two samples, are they independent or paired/matched?
4. Choose the test. Make sure the assumptions of the test are not violated

ASSUMPTIONS OF CHI-SQUARE TEST OF INDEPENDENCE
1. Nominal data (ordinal data also OK)
2. 25 =< n ="<250">
3. Random sample
4. Expected value of each cell is at least 5 (if not, you should combine some of the categories)

INTERPRETING RESULTS OF CHI-SQUARE TEST
H0 is "There is no association between religion and ethnicity. Any association seen is due to chance alone"
H1 is "There is a statistically significant association between religion and ethnicity "
Reject H0 if the calculated chi-square equals or exceeds the critical value
Reject H0 if p is less than or equal to 0.05 (if testing at alpha = 0.05)

ASSUMPTIONS OF T-TEST FOR TWO INDEPENDENT SAMPLES
1. Random
2. Interval data
3. Normal distribution in both groups
4. Preferably n <>

INTERPRETING RESULTS OF T-TEST
H0 is "There is no difference between mean heights of Chinese and mean heights of Japanese. Any difference seen is due to chance alone"
H1 is "There is a difference between mean heights of Chinese and mean heights of Japanese "
Reject H0 if the calculated t statistic equals or exceeds the critical value
Reject H0 if p is less than or equal to 0.05 (if testing at alpha = 0.05)

IMPORTANT: What is STATISTICALLY SIGNIFICANT may not be CLINICALLY SIGNIFICANT.

CORRELATION AND REGRESSION
Correlation: a measure of how two variables go together.
Pearson's r (also called Pearson's correlation coefficient) is a measure of linear relationship between two variables.
A value of +1 means a perfect positive linear relationship.
A value of -1 means a perfect negative linear relationship.
A value of 0 means no linear relationship.

Assumptions for using Pearson's r:
ü Randomness
ü Linear relationship exists
ü Both variables are normally distributed
ü Variables measured at Interval level

It is incorrect to use r for variables measured at nominal or ordinal level
Correlations can also be nonlinear. For nonlinear correlations, we do not use Pearson's r but some other correlation coefficient.

NOTE: CORRELATION DOES NOT IMPLY CAUSATION
Just because two variables are correlated does not necessarily mean that one causes the other.
Regression: used to predict how independent variables affect a dependent variable (Y)

Simple Regression: Has only 1 dependent variable Y and 1 independent variable
Multiple Regression: Has 1 dependent variable Y but two or more independent variables X1, X2 etc
Example
Simple regression - predict INCOME (Y) from YEARS OF EDUCATION (X)
Multiple regression - predict INCOME (Y) from YEARS OF EDUCATION (X1) and YEARS OF WORKING EXPERIENCE (X2)
(Variables measured at the nominal level such as "SEX" can also be used as independent variables in regression. They are used as "dummy variables").

r-square: An indicator of the "amount of variance of the dependent variable accounted for" by the regression equation. Also called the coefficient of determination.
The higher the r-square, the better the regression line fits the data.

Regression coefficient: If we have a regression equation Y = 0.3X1 + 4X2, then the regression coefficient of X1 is 0.3 and the regression coefficient of X2 is 4.This means that when X1 increases by 1 unit, Y will increase by 0.3Also, when X2 increases by 1 unit, Y will increase by 4 units.
Example
Diastolic blood pressure of sample of men aged 30-50 are plotted against their age
Y = 40 + 1.5X
(Y = diastolic blood pressure, X = age)
Interpretation: For these men, each year of increase in age raises the diastolic B.P. by 1.5 mm Hg
If man is 50 years old, the predicted diastolic bp is 40 + 1.5(50) = 115 mm Hg

NOTE: It is incorrect to extrapolate in regression analysis i.e. if your sample consists of men aged 30 - 50, you should not use the regression model to predict the blood pressure of men whose ages are below 30 or above 50
WHAT TO LOOK FOR IN A GOOD REGRESSION MODEL
1. Are the dependent variable and independent variables properly "operationalised" (defined and measured)?
2. Do the relationships between the dependent variable and independent variables make sense?
3. Is the relationship between the dependent variable and each independent variable linear in nature? Do scatterplots
4. Examine the r-square. The higher the r-square, the "better" the model.
5. Examine the sign of each regression coefficient. Do they make sense?
6. Check if each of the regression coefficients are statistically significant (p =< p ="<">
7. If there are more than one regression model, compare and contrast between them

OTHER TERMS TO KNOW
Confidence Interval: The interval within which something is likely to be found
A 95% Confidence Interval for the population mean indicates that there is a 95% probability that the population mean actually lies within that particular Confidence Interval.
Skew: If a curve is slanted to the right, it is skewed to the left.
If a curve is slanted to the left, it is skewed to the right
Nonparametric Tests: Statistical tests which make no assumptions about the parent distribution. Tests involving ranks of data are nonparametric.
Parametric Tests: Statistical tests which assume that the population distribution has a particular form e.g. a normal distribution. The t-test is a parametric test as it assumes normal distribution.
Standard Error of the Mean: We take samples from a population. For each sample, we calculate its mean. We then plot the sample means and we will get a curve. The curve will have a standard deviation. This standard deviation is the standard error of the mean. It is used to calculate confidence intervals.
The smaller the standard error of the mean, the more closely the sample mean estimates the true population mean.

3 - community medicine mcqs - 21 to 30

21) Cyclops intermediate host for

a. Guinea worm

b. Malaria

c. Rabies

d. Salmonella

Answer : a) Guinea Worm

Reference: Park 18^th Edition Page 588

22) The drug which is used only in RNTCP cat III is

a. Streptomycin

b. INH

c. Rifampicin

d. Pyz

Answer : a) Streptomycin

Reference: Park 18^th Edition Page 153

23) A carrier who gets infected from another carrier is called

a. Incubatory carrier

b. Paradoxical carrier

c. Convalescent carrier

d. Pseudo carrier

Answer : ???

Reference: Still referring

24) Eugenics is

a. the study of hereditary improvement of the human race by controlled selective breeding.

b. the humane destruction of an animal accomplished by a method that produces rapid unconsciousness and subsequent death without evidence of pain or distress, or a method that utilizes anesthesia produced by an agent that causes painless loss of consciousness and subsequent death

c. A feeling of well-being or elation; may be drug related.

d. a state of being carried away by overwhelming emotion

Answer : the study of hereditary improvement of the human race by controlled selective breeding.

Reference: Park 18^th Edition

25) Silicosis affects

a. Lower lobes of lungs

b. Upper lobes of lungs

c. Both

d. Hilum of lungs

Answer : Upper lobes

Reference: Park 18^th Edition Page 609

26) DDT is a

a. Organochlorine compound

b. Organophosphorus compound

c. Carbamate

d. Stomach poison

Answer : Organochlorine compound

Reference: Park 18^th Edition Page 589

27) Kala Azar is transmitted by

a. Phlebotomus sergenti

b. Phlebotomus papatasii

c. Phlebotomus argentipes

d. All of the above

Answer : Phlebotomus argentipes

Reference: Park 18^th Edition Page

28) Food poisoning is an example of

a. Common source, single exposure epidemic

b. Common source, continuous exposure epidemic

c. Propagated epidemic

d. Modern epidemic

Answer : a) Common source, single exposure epidemic

Reference: Park 18^th Edition Page 58

29) Cysticercosis cellulosae causes infection with

a. Taenia saginata

b. Taenia solium

c. Echinococcus granulose

d. Diphyllabatrium latum

Answer : b) Taenia Solium

Reference: Chaterjee Parasitology 12^th Edition Page 119

30) Following are correct about Autosomal recessive except

a. Both boy and girl are affected

b. Heterozyte are not affected

c. Most disorders of inborn errors of metabolism come under this group

d. Affect more people in later age group than children

Answer : d) Affect more people in later age group than children

Reference: Park 18^th Edition Page

2 - community medicine mcqs - 11 to 20

11) Main purpose of BCG given in child

a. To prevent all forms ot TB

b. To prevent the severe form of TB

c. To prevent severe complications

d. To control All forms of TB

Answer (d) to control all forms of TB

Reference: Park 18^th Edition Page 157

12) Which of the following is a wrong statement about Typhoid

a. Pea soup Diarrhoea

b. In the first week it is confirmed by Blood culture

c. Chronic Carrier Excrete bacilli for long time in Urine and Faeces

d. None of the above

Answer (d) none of the above

Reference: Park 18^th Edition Page 188

13) High Fibre Diet

a. Modifies the stool transit time

b. Decreases incidence of colon cancer

c. Both

d. None

Answer (c) Both

Reference: Park 18^th Edition Page 470

14) Complication of Varicella are All Except

a. CNS Involvement

b. Varicella Pneumonia

c. Myocarditis

d. Congenital Varicella

Answer (d) Congenital Varicella

Reference: Harrison 16^th Edition Page 1043

15) Asbestos exposure causes

a. Mesothelioma

b. Tetralogy of Fallot

c. Cerebral Palsy

d. Repeated Abortions

Answer (a) Mesothelioma

Reference: Park 18^th Edition Page 618

16) The vital layer of Slow sand filter is

a. Supernatant water

b. Schmutzdecke

c. Under-drainage system

d. Filter control valves

Answer : b) Schmutzdecke

Reference: park 18^th Edition Page 525

17) Helpline for AIDS can be reached by dialing

a. 1079

b. 1097

c. 1091

d. 1098

Answer : b) 1097

Reference: Park 18^th Edition Page 339

18) Paris Green is used to eliminate the larva of

a. Anophylline

b. Culex

c. Aedes

d. mansonoides

Answer : a) Anopheles

Reference: Park 18^th Edition Page 579

19) Origin of SPM dates back to

a. 17^th Century

b. 18^th Century

c. 19^th Century

d. 20^th Century

Answer : b) 18^th Century

Reference: Park 18^th Edition Page 5

20) Man is an host with dead end transmission in all of the following except

a. Malaria

b. Rabies

c. Tetanus

d. Japenese encephalitis

Answer : a) Malaria

Reference: Park 18^th Edition Page 228

1 - community medicine mcqs - 1 to 10

1) Maximum level of Chloride in Drinking water is

a. 600 mg/L

b. 500 mg/L

c. 300 mg/L

d. 200 mg/L

Answer (d) 200 mg/L

Reference: Park 18^th Edition Page 533

2) North India most comon congenital lesion

a. Neural Tube defects

b. Cleft Palate

c. Club foot

d. Congenital Heart diseases

Answer : (a) Neural Tube Defects

Reference: Park 18^th Edition Page 424

In the whole of North India, Neural Tube defects or Spina bifida are the most common birth defects

3) Which one of the following is oraganophosporous poison

a. Physostigmine

b. Dyflos

c. Tacrine

d. Edrophonium

Answer (b) DYflos

Reference: KDTripathi 5^th Edition Page

4) The response which is graded by an observer on an agree or disagree continuum is based on:

a. Visual analog scale.

b. Guttman Scale.

c. Likert Scale.

d. Adjectival scale.

Answer : 3.Likert Scale.

Reference

http://www.ndhcri.org/pain/Tools/Visual_Analog_Pain_Scale.pdf

http://trochim.human.cornell.edu/kb/scalgutt.htm

http://trochim.human.cornell.edu/kb/scallik.htm

http://acl.ldc.upenn.edu/P/P93/P93-1023.pdf

Visual Analog Scale

The Worst Imaginable Pain

|

|

|

|

|

No Pain

Instructions: Show and read the pain scale to the patient. Explain to the patient to place a mark along the line to indicate their current pain level. Wait for a verbal reply or for the patient to mark their current level of pain. Repeat the directions if the patient is having difficulty; use words other than "pain": aching, cramping, sore, uncomfortable, stiff, dull, pressure, burning, shooting. If the patient does not like it or understand it, switch to another pain rating scale. Always use the same scale for each follow-up assessment. Document the scale used as the Visual Analog Scale.

More at http://www.ndhcri.org/pain/Tools/Visual_Analog_Pain_Scale.pdf

Guttman Scale

Guttman scaling is also sometimes known as cumulative scaling or scalogram analysis. The purpose of Guttman scaling is to establish a one-dimensional continuum for a concept you wish to measure

More at http://trochim.human.cornell.edu/kb/scalgutt.htm

Likert Scale

You're now ready to use your Likert scale. Each respondent is asked to rate each item on some response scale. For instance, they could rate each item on a 1-to-5 response scale where:

1. = strongly disagree

2. = disagree

3. = undecided

4. = agree

5. = strongly agree

There are a variety possible response scales (1-to-7, 1-to-9, 0-to-4). All of these odd-numbered scales have a middle value is often labeled Neutral or Undecided. It is also possible to use a forced-choice response scale with an even number of responses and no middle neutral or undecided choice. In this situation, the respondent is forced to decide whether they lean more towards the agree or disagree end of the scale for each item.

More at http://trochim.human.cornell.edu/kb/scallik.htm

Adjectival Scale

A linguistic scale is a set of words, of the same grammatical category, which can be ordered by their semantic strength or degree of informativeness (Levinson, 1983). For example, lukewarm, warm, and hot fall along a single adjectival scale since they indicate a variation in the intensity of temperature of the modified noun

In the case of adjectives, the above definition is commonly relaxed to replace the total order among the elements of the scale by a partial one, so that the elements of the scale may be partitioned into two groups (sub-scales), within each of which the order is total. The two sub-groups correspond to positive and negative degrees of the common property that the scale describes. For example, the set of adjectives {cold, lukewarm, warm, hot} are normally considered part of one scale, even though no direct ordering of semantic strength exists between cold and hot.

More at http://acl.ldc.upenn.edu/P/P93/P93-1023.pdf

5) Plastic Syringes are sterilized by

a. Gamma rays

b. Hot air Oven

c. Autoclave

d. Washing in Phenol

Answer (a) Gamma Rays

Reference: Ananthanarayanan 7^th Edition Page 30

6) Chronic carriers in salmonella are

a. Faecal Carrier

b. Urinary Carriers

c. Blood Carriers

d. None of the above

Answer (a) Faecal Carrier

Reference: Partk 18^th Edition Page 187

7) Oral Polio Vaccine is a

a. Live attenuated Vaccine

b. Killed Vaccine

c. Subunit vaccine

d. None of the above

Answer (a) Live attenuated Vaccine

Reference: Park 18^th Edition Page 165

8) Tuberculin test founded by

a. VONPirquet

b. Heaf

c. Robert Koch

d. Ehrlich

Answer (a) Von Pirquet

Reference: Park 18^th Edition Page 150

9) Dots therapy is used in

a. Tuberculosis

b. Lymphoma

c. Spina Bifida

d. Ebstein’s Anomaly

Answer (a) Tuberculosis

Reference: Park 18^th Edition Page 154

10) First case to that comes to the knowledge of the Investigator is

a. Index case

b. Primary Case

c. Clinical Case

d. Subclinical Case

Answer (a) Index Case

Reference: Park 18^th Edition Page 88