Type of statistical errors

Q) A Surgical thesis was completed but later found to have Type II  error. This means ?

a) Benefit is perceived when really there is none (false positive).

b) Benefit is missed when it was there to be found (false negative).

c) Sample size was wrong

d) None of the above

Statistics – Tests of significance

Q) To Study the effect of an antiviral  drug, we note down the initial viral load and then after  a month repeat viral load. What is the   the most appropriate statistical test of significance to test the change in viral load

(a) Paired t-test
(b) Unpaired or independent t-test
(c) Analysis of variance
(d) Chi-square test

Ans a) Paired t test

paired t test is used When comparing the same person results after giving a drug or doing a surgery or any intervention

A paired t-test is used when we are interested in the difference between two variables for the same subject. Often the two variables are separated by time

Unpaired t test

The unpaired two-samples t-test is used to compare the mean of two independent groups.

For example, suppose that we have measured the weight of 100 individuals: 50 women (group A) and 50 men (group B). We want to know if the mean weight of women  is significantly different from that of men In this case, we have two unrelated (i.e., independent or unpaired) groups of samples. Therefore, it’s possible to use an independent t-test to evaluate whether the means are different.

Chi-square test

The basic idea behind the test is to compare the observed values in your data to the expected values that you would see if the null hypothesis is true.

To determine whether the association between two qualitative variables is statistically significant

Analysis of Variance ANOVA example

A group of psychiatric patients are trying three different therapies: counseling, medication and biofeedback. You want to see if one therapy is better than the others.


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