Purpose of sampling distribution is to characterize sample-to-sample variation so statistical tests may be applied, to estimate error due to sampling (confidence limits) and to evaluate observed differences between samples. Distribution could be used for bioassays taken in hospitals, breweries, food-processing plants, and pharmaceutical plants

Nelson, B. A.

English

NASA Technical Reports Server

•--	 ruary 1975
	
B74-10289 
S
	 NASA TECH BRIEF 
Langley Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Micro-Organism Distribution Sampling for Bloassays 
The numbers and types of naturally occurring 
micro-organisms on surfaces are obtained by assay 
samples, taken either by swabs or by immersion and 
the ultrasonic treatment of representative portions. 
An acceptable sampling distribution must be avail-
able to relate observed assays to the number of micro-
organisms on a surface at the time of sampling before 
any valid statistical inferences can be made. This 
study provides the basis for the development of such a 
probability distribution, including its mathematical 
form, the rationale for selecting that form, the 
techniques for estimating the parameters of the distri-
bution, the verification of the resulting distribution 
using goodness-of-fit tests, and the methods (both 
exact and approximate) for computing confidence 
intervals. 
The purpose of this. sampling distribution is to 
characterize the sample-to-sample variation in order 
that statistical tests may be applied, to estimate the 
error due to sampling (confidence limits) and to 
evaluate observed differences between samples. It 
would be useful in processing bioassay data from any 
source. In addition to processing data taken from 
spacecraft hardware, this distribution could be used 
for bioassays taken in hospitals, in breweries, and also 
in food-processing and pharmaceutical plants. 
The sampling distribution for bioassays was 
developed from the assumption that micro-organisms
occur on surfaces in clumps which are distributed 
randomly and independently. The number of micro-
organisms per clump has a probability distribution 
specified by three parameters: the probability of one 
organism, the probability of two or more, and the 
maximum number of organisms per clump. This 
distribution has produced an acceptable goodness-of-
fit to bioassay data from the Mariner .1969 space 
missions, and it was used to compute confidence 
limits for the number of micro-organisms present. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Langley Research Center 
Mail Stop 139-A 
Hampton, Virginia 23665 
Reference: B74-10289 
Patent status: 
NASA has decided not to apply for a patent. 
Source: Bruce A. Nelson of
Martin Marietta Corp.

under contract to

Langley Research Center 
(LAR-10789) 
I
Category: 05 (Life Sciences) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants .ihat such use 
Government nor any person acting on behalf of the United States
	
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19740000289 2020-03-17T14:18:54+00:00Z


Micro-organism distribution sampling for bioassays

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