Location test




A location test is a statistical hypothesis test that compares the location parameter of a statistical population to a given constant, or that compares the location parameters of two statistical populations to each other. Most commonly, the location parameter (or parameters) of interest are expected values, but location tests based on medians or other measures of location are also used.



One-sample location test


The one-sample location test compares the location parameter of one sample to a given constant. An example of a one-sample location test would be a comparison of the location parameter for the blood pressure distribution of a population to a given reference value. In a one-sided test, it is stated before the analysis is carried out that it is only of interest if the location parameter is either larger than, or smaller than the given constant, whereas in a two-sided test, a difference in either direction is of interest.



Two-sample location test


The two-sample location test compares the location parameters of two samples to each other. A common situation is where the two populations correspond to research subjects who have been treated with two different treatments (one of them possibly being a control or placebo). In this case, the goal is to assess whether one of the treatments typically yields a better response than the other. In a one-sided test, it is stated before the analysis is carried out that it is only of interest if a particular treatment yields the better responses, whereas in a two-sided test, it is of interest whether either of the treatments is superior to the other.


The following tables provide guidance to the selection of the proper parametric or non-parametric statistical tests for a given data set.



Parametric and nonparametric location tests


The following table summarizes some common parametric and nonparametric tests for the means of one or more samples.


















































































Ordinal and numerical measures
1 group


N ≥ 30

One-sample t-test

N < 30
Normally distributed
One-sample t-test
Not normal

Sign test
2 groups
Independent

N ≥ 30


t-test

N < 30
Normally distributed

t-test
Not normal

Mann–Whitney U or Wilcoxon rank-sum test
Paired

N ≥ 30

paired t-test

N < 30
Normally distributed
paired t-test
Not normal

Wilcoxon signed-rank test
3 or more groups
Independent
Normally distributed
1 factor

One way anova
≥ 2 factors
two or other anova
Not normal


Kruskal–Wallis one-way analysis of variance by ranks
Dependent
Normally distributed

Repeated measures anova
Not normal


Friedman two-way analysis of variance by ranks















































Nominal measures
1 group


np and n(1-p) ≥ 5

Z-approximation

np or n(1-p) < 5

binomial
2 groups
Independent

np < 5

fisher exact test or Barnard's test

np ≥ 5

chi-squared test
Paired


McNemar or Kappa
3 or more groups
Independent

np < 5
collapse categories for chi-squared test

np ≥ 5

chi-squared test
Dependent


Cochran´s Q








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