Test 185  (Statistics)

1. A recently discovered treatment for retinoblastoma significantly 
    extends the lifespan of the patient, but does not prevent the disease 
    or lead to its cure. Given this scenario, which of the following 
    statements about  retinoblastoma is (are) true?

a. its incidence will increase.

b. its prevalence will increase.

c. its incidence will decrease.

d. its prevalence will decrease.

e. both the incidence and prevalence will increase

 
Answera.F   b.T  c.F   d.F  e.F
As the length of survival from retinoblastoma increases because of the new treatment (assuming the rate of new cases diagnosed remains unchanged), the number of cases present at any point in time (prevalence) increases. Incidence, based on the number of new cases only, remains unchanged.

2. A random selection of 1200 adults agree to participate in a study of 
    the possible effects of drug X. They are followed prospectively for a 
    period of five years to see if there is an association between the 
    incidence of cataract and the use of drug X. This type of study is a:

a. case-control study.

b. randomized controlled clinical trial.

c. cross-sectional study.

d. cohort study.

e. cross-over study.

 

Answera.F  b.F  c.F  d.T  e.F
In a case-control study cases (those with the problem) are compared with controls (those without the problem) with regard to the incidence of a specific risk factor (such as use of the pill).

In a randomized controlled clinical trial some members

of a cohort with a particular condition are given one treatment while others receive a different (often 'standard') treatment or placebo.

A cross-sectional study is a 'snapshot' or 'point in time'

study.

In a cross-over study patients are exposed to at least two 

treatment modalities (+/- placebo) in sequence. The order of exposure to the different treatments is determined by the experimental design and is often random.

 
 

3. 'Validity' as applied in statistics refers to:
 

a. expresses the degree to which two things are related.

b. implies that the results of a test can be reproduced.

c. describes how well a study measures what it purports 
    to measure.

d. measures the strength of relationship between cause 
    and effect.

e. indicates the probability of obtaining a given result by 
    chance alone.

 

Answer
a.F   b.F  c.T  d.F  e.F
'Association' expresses the degree to which two things are related.
Reliability implies that the results of a test can be reproduced.
Validity describes how well a study measured what it was designed to measure. 
Relative risk measures the strength of a cause-and-effect relationship.
The P-value indicates the probability of obtaining a given result by chance.
.

 

. 4. In a trial of a new drug the following results were obtained: 
      treatment group 54 improved 26 not improved, placebo group 56 
      improved 21 not improved.

a. the results so obviously show the benefit of treatment 
    that statistical analysis is not required

b. the data could be evaluated using the chi-squared test

c. Pearson's coefficient of linear regression would be an 
    appropriate significance test

d. the numbers are too small to draw any conclusions

e. a Student t-test could be used

Answer
a.F  b.T  c.F  d.F  e.F
Statistical analysis should be carried out as nothing is ever that obvious.
These data are ideal for a chi-squared test.
There is no linear regression to plot.
The number in this study is not small.
The study compares proportions and not means and therefore a Student t-test is not appropriate.

5. For the data series: 2, 1, 6, 4, 2

a. the mode is 4

b. the median is 3

c. the standard deviation is 4

d. the mean is 3

e. the mean is always identical to the median

 
Answer
a.F   b.F  c.F  d.T  e.F
Mean = 3:  ((2+1+6+4+2)/5)
Mode = 2: (The commonest value)
Median = 2: (The middle value)
SD = 2: (Square root of the sum of (1-3)squared + (1-3)squared + (6-3)squared + (4-3)squared + (2-3)squared / (5-1)

 

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