Considering normal distribution, which one of the following statements is incorrect?
D. Irrespective of the number of observations made, the shape of a normally distributed curve is symmetric and bell shaped. The exact shape of the normal distribution is defined by a function that has only two parameters: mean and standard deviation. For a given range of scores, when the standard deviation is small, the curve becomes leptokurtic, i.e. thin but still symmetric. When the standard deviation is larger, it becomes platykurtic.
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In descriptive statistics, which of the following is the most widely used measure of dispersion of a frequency distribution?
C. Standard deviation is a widely used measure of dispersion of data in descriptive statistics. Other measures include range, interquartile range (usually accompanies median values), and variance. Standard deviation is obtained by the root mean square of differences between individual observations and the mean value. Note that standard error is often preferred as the measure of dispersion while making inferences from a sample of the population. Standard error is a measure of precision of sample estimate in comparison with the population value.
In qualitative research which of the following refers to modifying the research methods and hypothesis as and while one conducts the research?
B. The iterative approach in qualitative studies refers to the process of altering the research methods and building the hypothesis as the study progresses, in response to new information gained while conducting the research. This flexibility allows qualitative studies to follow an inductive rather than the deductive approach seen in quantitative research. Data come before theory is generated in inductive methods; a stated theory is tested using generated data in deductive methods.
Systolic blood pressure is known to be normally distributed across the population with a mean of 120 mmHg and standard deviation of 10 mmHg.
How many out of 100 patients in a population will have systolic blood pressure between 120 and 130 mmHg?
E. In the above question, the mean is given as 120 mmHg. Assuming normal distribution with a standard deviation of 10 mmHg, we can find out the proportion of the population that will fall between two observed values. For values between –1 and +1 standard deviation from the mean, this will be nearly 68%. Nearly 34% will have values between the mean and 1 standard deviation. In other words 34% will have systolic blood pressure between 120 mmHg and 130 mmHg.
In which of the following situations is intention to treat analysis deliberately not attempted even if there are significant numbers of drop-outs?
A. Significant numbers of subjects recruited for trials often do not complete the trial as per protocol. The data generated from such drop-outs cannot be ignored as this will potentially lead to an attrition bias in favour of the intervention generally. Therefore, it is a standard practice to analyze the results of trials on an ‘intention to treat’ basis, i.e. data from subjects are analyzed as per initial allocation irrespective of trial completion. In a few situations such as the ‘efficacy studies’, intention to treat analysis is not used, instead ‘per-protocol analysis’ is carried out. An efficacy study is designed to explain the effects of the intervention itself. This is in contrast to effectiveness studies, which are designed to study the usefulness of making an intervention available (choices B, C and D).
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