Usage Note 22427: Can I test for Uniform distribution?
Details About Rate It
Yes. The Uniform distribution is a special case of the Beta distribution with α = β = 1. You can test that the data are from a uniform distribution in PROC UNIVARIATE or in SAS/QC PROC CAPABILITY. In any of the statements that accept distribution options (such as the HISTOGRAM statement), use the options A=1 and B=1 with the BETA distribution option to test for uniformity. Use the THETA= and SIGMA= options to establish the lower and upper limits of support. Set THETA= to the lower limit. Set SIGMA= to the range between the upper and lower limits. For instance, to test that the input data are distributed U(10,25), specify the option: BETA(A=1 B=1 THETA=10 SIGMA=15).
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For poissson
Re: How to test Poisson Distribution?
Paul R Swank
Tue, 28 May 2002 11:47:07 -0700
Why can't you run a poisson regression model with no predictors and look at
the fit of the model. I generated 1000 Poisson x's and then fit to a poisson
using genmod in sas. The Pearson chi-square below is not significant
indicating fit. the mean is exp(intercept) = exp(-0.0253) = .975 which is
close to the mean of 1 that I specified.
The GENMOD Procedure
Model Information
Data Set WORK.TEMP1
Distribution Poisson
Link Function Log
Dependent Variable y
Observations Used 1000
Criteria For Assessing Goodness Of Fit
Criterion DF Value
Value/DF
Deviance 999 1143.3883
1.1445
Scaled Deviance 999 1143.3883
1.1445
Pearson Chi-Square 999 993.2051
0.9942
Scaled Pearson X2 999 993.2051
0.9942
Log Likelihood -999.6849
Algorithm converged.
Analysis Of Parameter Estimates
Standard Wald 95% Confidence
Chi-
Parameter DF Estimate Error Limits
Square Pr > ChiSq
Intercept 1 -0.0253 0.0320 -0.0881 0.0375
0.62 0.4292
Scale 0 1.0000 0.0000 1.0000 1.0000
NOTE: The scale parameter was held fixed..
Paul R. Swank, Ph.D.
Professor, Developmental Pediatrics
Medical School
UT Health Science Center at Houston
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
Behalf Of Chia C Chong
Sent: Sunday, May 26, 2002 5:38 PM
To: [EMAIL PROTECTED]
Subject: How to test Poisson Distribution?
I have a random variable,X with 1000 samples (all discrete values). I want
to test whether X can sastify a Poisson process or not. How should I test
it?
THanks.
CCC
.
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For bionomial distribution
http://www.ats.ucla.edu/stat/sas/whatstat/whatstat.htm
Binomial test
A one sample binomial test allows us to test whether the proportion of successes on a two-level categorical dependent variable significantly differs from a hypothesized value. For example, using the hsb2 data file, say we wish to test whether the proportion of females (female) differs significantly from 50%, i.e., from .5. We will use the exact statement to produce the exact p-values.
proc freq data = "c:\mydata\hsb2";
tables female / binomial(p=.5);
exact binomial;
run;
The FREQ Procedure
Cumulative Cumulative
female Frequency Percent Frequency Percent
-----------------------------------------------------------
0 91 45.50 91 45.50
1 109 54.50 200 100.00
Binomial Proportion for female = 0
-----------------------------------
Proportion (P) 0.4550
ASE 0.0352
95% Lower Conf Limit 0.3860
95% Upper Conf Limit 0.5240
Exact Conf Limits
95% Lower Conf Limit 0.3846
95% Upper Conf Limit 0.5267
Test of H0: Proportion = 0.5
ASE under H0 0.0354
Z -1.2728
One-sided Pr < Z 0.1015
Two-sided Pr > |Z| 0.2031
Exact Test
One-sided Pr <= P 0.1146
Two-sided = 2 * One-sided 0.2292
Sample Size = 200
The results indicate that there is no statistically significant difference (p = .2292). In other words, the proportion of females in this sample does not significantly differ from the hypothesized value of 50%.
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