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Biostatistics

Question
55 out of 76
 

A study was conducted on alcoholics before and after consumption. The statistical method used to find significance is (DNB Jan 2009)



A Chi square test
B Unpaired t test

C Paired T test
D Mann Whitney test

Ans. C Paired T test Ref. High yield biostatistics; Pg: 66

Tests of Significance

This question must again be interpreted very carefully as very limited information is furnished. The only hint we have in this question is that it is a before after study or a paired or matched design as the same group of people are providing the data at two different time points.

Hence the answer is Paired T test as all the other tests mentioned in this question are unpaired tests which are performed when there are two groups providing the data.

SIGNIFICANCE TESTS: TYPES

The type of significance test used depends on whether the data is parametric (usually normally distributed) or non-parametric

Parametric tests

Student's t-test - paired on unpaired

Pearson's - correlation

Paired data refers to data obtained from a single group of patients, e.g. measurement before and after an intervention.

Un-paired data comes from two different groups of patients, e.g. comparing response to different interventions in two groups.

Parametric tests: These are - t test, z-test and ANOV A (or F-test) These share few common features:­

(i) These hypothesis refers to certain population parameters which is the population mean (in case of t and z tests) or the population variance (in case of F test)

(ii) These hypothesis concern interval or ratio scale data (e.g. weight, height, BP etc)

(iii) They assume that the population data are normally distributed.

Z-Test:

  1. Involves the same steps as t-test
  2. Used when the sample is large (n> 100). When the total no. of observations is ≤100, use T test in place of Z test.
  3. T-test though is more important as there is no ­situation where as Z test can be used and a t-test cannot be but the vice versa can occur.

ANOVA:

Whereas a T test is appropriate for making just one comparison (between two sample means, or between a sample mean and a hypothesized population mean), when more than one comparison is being made (i.e. when means of> 2 groups are being compared), ANOVA (analysis of variance) is the appropriate technique.

Non-parametric tests

Wilcoxon matched-pairs - compares the medians obtained

Mann-Whitney - unpaired data

Spearman, Kendall rank - correlation

Chi-squared test - used to compare proportions or percentages

Chi-square test offers alternate method of testing significance of difference between two proportions.

More than 2 groups can be compared.

Test Null Hypothesis, applying Chi-square test, finding degree of freedom and probability tables are components.

When p valve is <0.05 null hypothesis is true and the study is rejected, and vice versa.

Testing the null hypothesis =

Tests of significance:

Questions Concerning

Nominal

Ordinal

Interval/Ratio

Differences in proportion

X2 test

-

-

One or two means

‘t’ or ‘z’ test

When n≤ 100: T test

When n > 100: Z test

More than two means

ANOVA with F test

Biostatistics Flashcard List

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