Test 33 (Statistics and epidermiology) 1. A normal population distribution is needed for the following statistical      tests: a. chi-squared b. variance estimation c. standard error of the mean d. Student's t-test e. Kendall's rank coefficient. Answera.F   b.T  c.T   d.T   e.F Non-parametric tests make no assumptions about the underlying distribution of the sample. Parametric tests assume that the population form which samples are taken should be normal distributed. Kendall's and Spearman's rank correlation coefficients are the non-parametric tests whereas Pearson's correlation coefficient is a parametric test.   2. With regard to statistics: a. the mode is the most frequently occurring value b. the mode is the maximum point on a frequency distribution      curve. c. the median has an equal number of values above and below       it d. in a normal distribution the mean, mode and median coincide e. about 95% of observations lie within two standard       deviations of the mean Answera.T   b.T   c.T   d.T   e.T 3. With regard to the chi-squared test: a. it is used to test the difference between frequencies b. it is used as an alternative to the t-test to determine the      difference between two means c. the number of degrees of freedom is the number of      independent comparisons. d. the greater the value of the chi-squared test, the less likely it       is to be significant e. the null hypothesis is not required. Answera.T   b.F   c.T   d.F   e.F Chi-squared test is used to determine the difference between observed and expected frequencies or between two or more frequencies. The larger the value the smaller the probability p, and the more likely it is that the null hypothesis is untrue.   4. The prevalence rate of a disease has the following features: a. it is dependent on the incidence of the disease b. it is dependent on the duration of illness c. it measures all the current cases in the community d. it can be estimated from a cross-sectional study e. it can be used to determine the health needs of a community Answera.T   b.T   c.T   d.T   e.T Prevalence rate = the number of current cases (both old and new) of a specified disease during a specified time period divided by the estimated mid-interval population at risk. As the prevalence rate includes all cases in the community, it is determined by both the incidence and the duration of the disease process. 5. An aetiological factor must satisfy the following before one can say that it      is causally related to a disease: a. exposure to the factor must precede the development of the      disease b. elimination of the factor decreases the risk of the disease c. the factor is found more frequently among the diseased than      non-diseased d. the factor is not found among persons without the disease e. the factor is found in all cases with the disease Answera.T   b.T   c.T   d.F   e.F