MATLAB: How to determine if the data follows a lognormal distribution

lognormalMATLABStatistics and Machine Learning Toolbox

My x-data includes arrival time for cells and my y-data includes their velocities. How can I determine if this data set follows a lognormal distribution?

I've already tried QQ-plots and histograms, but am utterly lost on how to approach this.

Thanks.

Best Answer

If all your data are positive, that’s a good start. I’m not sure what you’re studying, but I always associate ‘arrival times’ with the Poisson distribution (that ‘looks’ a lot like the lognormal distribution). The velocities may well be lognormally distrbuted. I suggest using the histfit function for both. Another option is to use the chi2gof function to perform a Chi-square goodness-of-fit test.

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MATLAB: How to check whether the distribution of the data is a right/left skewed normal distribution using kolmogorov-smirnov test

If your data points were positive, they would look like Gamma or Chi-square distribution. Type distributionFitter in the command window and to open the distribution fitter app. There you will have options to easily fit multiple distributions and find the right one.

MATLAB: How to go about finding the standard normal probability based on the z-score

doc normcdf
doc normpdf

When you know what you want but not sure the name, try something like

>> lookfor normal
realmin                        - Smallest positive normalized floating point number.
randn                          - Normally distributed pseudorandom numbers.
sprandn                        - Sparse normally distributed random matrix.
surfnorm                       - Surface normals.
isonormals                     - Isosurface normals.
cde                            - cd elliptic function with normalized complex argument.
sne                            - sn elliptic function with normalized complex argument.
addfreqcsmenu                  - Add a cs menu to switch between linear and normalized frequency
convertfrequnits               - converts between Normalized, Hz, kHz, etc
histfit                        - Histogram with superimposed fitted normal density.
jbtest                         - Jarque-Bera hypothesis test of composite normality.
lhsnorm                        - Generate a latin hypercube sample with a normal distribution
logncdf                        - Lognormal cumulative distribution function (cdf).
lognfit                        - Parameter estimates and confidence intervals for lognormal data.
logninv                        - Inverse of the lognormal cumulative distribution function (cdf).
lognlike                       - Negative log-likelihood for the lognormal distribution.
lognpdf                        - Lognormal probability density function (pdf).
lognrnd                        - Random arrays from the lognormal distribution.
lognstat                       - Mean and variance for the lognormal distribution.
mvncdf                         - Multivariate normal cumulative distribution function (cdf).
mvnpdf                         - Multivariate normal probability density function (pdf).
mvnrnd                         - Random vectors from the multivariate normal distribution.
normcdf                        - Normal cumulative distribution function (cdf).
normfit                        - Parameter estimates and confidence intervals for normal data.
norminv                        - Inverse of the normal cumulative distribution function (cdf).
normlike                       - Negative log-likelihood for the normal distribution.
normpdf                        - Normal probability density function (pdf).
normplot                       - Displays a normal probability plot.
normrnd                        - Random arrays from the normal distribution.
normspec                       - Plots normal density between specification limits.
normstat                       - Mean and variance for the normal distribution.
logn3fit                       - Fit a 3-param lognormal dist'n using cumulative probabilities.
wgtnormfit                     - Fitting example for a weighted normal distribution.
wgtnormfit2                    - Fitting example for a weighted normal distribution (log(sigma) parameterization).
>>

Judicious search terms help but seeing the list of things related to "normal" lets you find the two functions of interest (plus a lot more depending upon which toolboxes are available, maybe) that might be of use/interest...

Best Answer

Related Solutions

MATLAB: How to check whether the distribution of the data is a right/left skewed normal distribution using kolmogorov-smirnov test

MATLAB: How to go about finding the standard normal probability based on the z-score

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