How do you test for normality of data?
How do you test for normality of data?
The two well-known tests of normality, namely, the Kolmogorov–Smirnov test and the Shapiro–Wilk test are most widely used methods to test the normality of the data. Normality tests can be conducted in the statistical software “SPSS” (analyze → descriptive statistics → explore → plots → normality plots with tests).
What is Kolmogorov-Smirnov test used for?
The Kolmogorov-Smirnov test (Chakravart, Laha, and Roy, 1967) is used to decide if a sample comes from a population with a specific distribution. where n(i) is the number of points less than Yi and the Yi are ordered from smallest to largest value.
What is a KS test in statistics?
In statistics, the Kolmogorov–Smirnov test (K–S test or KS test) is a nonparametric test of the equality of continuous (or discontinuous, see Section 2.2), one-dimensional probability distributions that can be used to compare a sample with a reference probability distribution (one-sample K–S test), or to compare two …
How do you use Kolmogorov-Smirnov test?
The general steps to run the test are:
- Create an EDF for your sample data (see Empirical Distribution Function for steps),
- Specify a parent distribution (i.e. one that you want to compare your EDF to),
- Graph the two distributions together.
- Measure the greatest vertical distance between the two graphs.
How do you tell if a sample is normally distributed?
A normal distribution is one in which the values are evenly distributed both above and below the mean. A population has a precisely normal distribution if the mean, mode, and median are all equal. For the population of 3,4,5,5,5,6,7, the mean, mode, and median are all 5.
What is the p value for Kolmogorov Smirnov test?
It accepts the null hypothesis since p-value 0.1954 > 0.05 = – a default value of the level of significance. According to this test, the difference between two samples is not significant enough to say that they have different distribution.
What is Lilliefors test for normal distribution?
There is a version of KS test, called Lilliefors test, that tests normality of the distribution by comparing the data with a fitted normal distribution as we did above, but with a correction to give a more accurate approximation of the distribution of the test statistic.
What is the difference between the Lilliefors test and Kolmogorov-Smirnov test?
Lilliefors created a related test that gives more accurate results in this case (see Lilliefors Test Table ). The Lilliefors test uses the same calculations as the Kolmogorov-Smirnov test, but the table of critical values in the Lilliefors Test Table is used instead of the Kolmogorov-Smirnov Table.
What is the K-S and Shapiro-Wilk normality test in SPSS?
SPSS provides the K-S (with Lilliefors correction) and the Shapiro-Wilk normality tests and recommends these tests only for a sample size of less than 50 (8). In Figure, both frequency distributions and P-P plots show that serum magnesium data follow a normal distribution while serum TSH levels do not.
How do I run a K-S test with Lilliefors correction?
If I choose ‘Analyze->Descriptive Statistics->Explore’ from the menus, click the Plots button and check “Normality plots with tests”, then the EXAMINE command is run and the K-S test with Lilliefors correction (for sample-based parameters) is printed.
