# ASTM D2525-13

Designation: D2525 − 13Standard Practice forSampling Wool for Moisture1This standard is issued under the fixed designation D2525; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the design of a sampling plan to beused to obtain samples for the determination of the moisturecontent of grease wool, scoured wool, carded wool, garnettedwool, wool top and intermediate products, and rovings.1.2 Directions are given for the designation of samplingunits, calculation of the number of sampling units required toachieve a preselected precision and confidence level or,alternatively, for calculating the confidence limits for the meanbased on the variability of the sample tested.NOTE 1—This practice for devising a sampling plan is intended for usein connection with Test Method D1576 or Test Method D2462. Thesampling of raw wool for the determination of clean wool fiber present iscovered in Practice D1060.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D123 Terminology Relating to TextilesD1060 Practice for Core Sampling of Raw Wool in Packagesfor Determination of Percentage of Clean Wool FiberPresentD1576 Test Method for Moisture in Wool by Oven-DryingD2462 Test Method for Moisture in Wool by DistillationWith TolueneD4845 Terminology Relating to WoolE122 Practice for Calculating Sample Size to Estimate, WithSpecified Precision, the Average for a Characteristic of aLot or Process3. Terminology3.1 For all terminology related to D13.13, Wool and Felt,see Terminology D4845.3.1.1 The following terms are relevant to this standard:laboratory sample, lot lot sample, sample, sampling unit,specimen.3.2 For definitions of all other textile terms see TerminologyD123.4. Summary of Practice4.1 Directions are given for subdividing a lot of materialinto potential sampling units and for providing each potentialsampling unit with its own unique identification.4.2 Directions are given for calculating the number of suchsampling units required to give a preselected allowable varia-tion at a stated probability level, or for calculating confidencelimits for the sample mean obtained for a given size of sample.4.3 Directions are given for deciding which particular sam-pling units should be chosen to constitute the required lotsample. These directions ensure that all potential samplingunits have approximately the same chance of being selected forthe lot sample.5. Significance and Use5.1 This recommended practice furnishes directions for thesampling of wool of the various forms indicated in Section 1,in order that correct probability statements may be made aboutthe relationship between the sample mean and the populationmean. If these statements are to be correct, certain conditions,which are stated, must hold.5.2 This recommended practice requires that a deliberate actof randomization be performed so that all potential samplingunits have approximately the same chance of being taken andno sampling unit is deprived of its chance of being taken.5.3 In any case where insufficient information about thevariability of the sampling units within the lot is available,directions are given for calculating confidence limits for thesample mean so that a correct probability statement can still bemade.1This practice is under the jurisdiction of the ASTM Committee D13 onTextilesand is the direct responsibility of Subcommittee D13.13 on Wool and Felt.Current edition approved July 1, 2013. Published August 2013. Originallyapproved in 1966. Last previous edition approved in 2008 as D2525 – 90 (2008).DOI: 10.1520/D2525-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16. Preliminary Conditions6.1 If it is desired to calculate a sample size to achieve apreselected precision at a preselected level of confidence,knowledge of the variation of the moisture content is neces-sary.6.1.1 The test method to be used must be the same methodthat was used to derive any prior information with respect tothe variability of the moisture content.6.1.2 The sampling unit must be the fundamental unit interms of which the variance is expressed. In other words, if thesampling unit is chosen to be a 25-g handful of bulk materialor a 4-yd (3.65-m) length of sliver, then the variance used mustbe the number that expresses the variability of these units, andthe number of sampling units which is calculated will be thenumber of such units required. The sampling unit is notnecessarily the same thing as a specimen.6.1.3 The lot designated for sampling must be statisticallyhomogeneous. This is equivalent to saying that the lot shall notbe composed of a mixture of two or more parts, the moisturecontent of which is distributed sufficiently differently that if themoisture content of the entire lot were measured, a plot of themoisture content versus the number of sampling units wouldshow a curve having more than one peak. (See Appendix X1.)If the test given in Appendix X1 leads to the conclusion that thelot cannot be considered to be statistically homogeneous, thenit should be subdivided into groups that are homogeneous. Thepattern of runs found may indicate what the subgroups shouldbe.6.1.4 The magnitude of the variation of moisture contentwithin the homogeneous lot must be known. The magnitude ofthe variation is usually expressed as the standard deviation,although the range may also be used.6.2 If insufficient knowledge is available to ensure meetingthe above conditions, a sample of convenient size may beselected and confidence limits calculated for the mean usingthe information in the sample results. In this case, the onlycondition that applies is 6.1.3.7. Procedure7.1 Designate the form and size of the sampling unit,bearing in mind the conditions and precautions discussed inSections 5 and 6. Whenever possible, make the size of thesampling unit and specimen the same.7.1.1 The designation of the sampling unit depends on theform of the material and on the method to be used for makingmeasurements on the sample. The material to be sampled mayexist in one of three basic forms: bulk material such as scouredwool or picked blends of wools, packaged material such asbaled wool, or material put up in the form of packages withinpackages such as balls of top within cases or bales. The methodof measurement may require a specimen as large as a wholepackage of material, or as small as a few grams of material.7.1.2 Where the material to be sampled exists in some bulkform, such as scoured wool, or a blend that has been picked andstored in a bin, the designation of a sampling unit will dependupon the mechanics of drawing the sample. If hand sampling isthe method employed, the sampling unit will be a handful of acertain specified size. Whenever possible, the size of a sam-pling unit should be made to coincide with the size of thespecimen required by the method of measurement because therandom variations observed in the test results are then directlyapplicable to the sampling units.7.1.3 When the material to be sampled exists in the form ofpackages such as baled wool or packages within packages,such as balls of wool top in cases or bales, the sampling unitcan be either an entire package or some portion of a package,depending upon the size of the specimen required.7.2 Identify each potential sampling unit in the lot bynumbering, coding, using geometrical coordinates, or by anyother systematic means. It is important that by some means orother, all potential sampling units must be furnished with theirown unique identification so that none is deprived of its chanceof being sampled.7.2.1 In designing a sampling plan, it is necessary to devisea method for assigning to every potential sampling unit in thelot a unique identification. This is a relatively simple task inthose instances where the sampling units are discrete packages,such as might be the case with balls of top if an entire ball isto be the sampling unit.7.2.2 With material in bulk form or with packaged materialin which the sampling unit is to be only a portion of thepackage, it is not as easy to identify uniquely each potentialsampling unit, and some method of approximating the idealsituation must be devised. See, for example, the instructionsgiven in Practice D1060.7.2.3 For materials in loose bulk form, considerable inge-nuity and imagination may be required to effect a properidentification of the potential sampling units.7.3 Option 1—This procedure is available for those in-stances where information is sufficient to enable the calculationof sample size required for a specified allowable variation andprobability level.7.3.1 If the allowable variation and probability level are notstated in the applicable material specification or otherwiseestablished, determine for these factors values mutually agree-able to all parties interested in the test results.7.3.2 Whenever the material being tested has been producedunder statisically controlled conditions and records areavailable, or information is available from prior tests on thesame lot, estimate the universe standard deviation from thesedata.NOTE 2—In many instances only an estimation of the variation likely tobe encountered in a lot is available, such as the limits beyond which valuesof moisture content are not likely to occur. Practice E122 includesformulas for estimating the standard deviation for different distributionsbased on the extreme range of values expected. Whenever there is noinformation available as to the form of the distribution, assuming arectangular distribution will yield a relatively conservative estimate.7.3.3 Based on values determined as directed in 7.3.1 and7.3.2, calculate the number of sampling units required, usingEq 1 or Table 1:n 5 ~t23 s2!/E2(1)D2525 − 132where:n = number of sampling units required rounded to the nexthigher whole number when the calculated value of n isequal to or less than 50 and rounded to the next highermultiple of five when the calculated value of n is greaterthan 50,t = constant depending on the desired probability level andequal to Student’s t for infinite degrees of freedom andtwo-sided limits, for example,Probability Level, % tt290 1.645 2.70695 1.960 3.84299 2.576 6.636s = standard deviation of individual observations, in units ofthe property being evaluated, andE = allowable variation of the test results expressed in unitsof the property being evaluated, which in some casesmay be a percentage.NOTE 3—The arbitrarily chosen value for E refers to the allowablevariation in a test result based on observations still to be carried out underconditions of single-operator precision.7.3.4 Using a table of random numbers or any satisfactoryobjective randomizing procedure, decide which particular po-tential sampling units will make up the sample of the sizecalculated in 7.3.3.7.3.5 Acquire these particular sampling units by the methodrequired by the designation done in 7.1, using special care toavoid gain or loss of moisture by the sampling unit in theprocess of being taken. Weigh these sampling units as rapidlyas possible as they are selected.7.4 Option 2—This procedure is available for those in-stances where enough information to apply Option 1 is notobtainable or for those instances where all parties interested inthe results of the test agree to accept whatever precision mayresult from an agreed upon fixed sample size and probability inorder to reduce the cost of testing.7.4.1 Decide, by agreement between the parties interested inthe test results, on the number of sampling units to be taken andthe confidence level desired.7.4.2 Proceed as directed in 7.3.4 and 7.3.5.7.4.3 After performing the tests, calculate the confidencelimits for the sample mean by Eq 2:Confidence limits 56ts/=n (2)where:n = number of sampling units in the sample,t = value of Student’s t for n − 1 degrees of freedom,two-sided limits, and the specification probabilitylevel,3ands = sample standard deviation, defined by Eq 3:s 5@(i~xi2 x¯ !2/~n 2 1!#1/2(3)NOTE 4—The xiin the above equation are individual values for samplingunits when the sampling unit and the specimen are the same size. When,however, more than one specimen is measured per sampling unit, the xiwill be averages of those specimens belonging to a particular samplingunit. x¯ is, of course, the grand average of all values.7.5 Having obtained a lot sample, there are alternative waysof acquiring specimens from it depending on the type ofinformation needed.7.5.1 Option 1 has been exercised and no information isneeded about variability:The entire lot sample is the laboratory sample. Condition thespecimen in accordance with Test Method D1576.7.5.2 Option 1 has been exercised and information aboutvariability is wanted, or Option 2 has been exercised:Example 1: The sampling unit is greater than or equal to thespecimen size—Each sampling unit is a laboratory sample. Condi-tion each laboratory sample in accordance with Test MethodD1576.Example 2: The sampling unit is less than the size of specimenrequired —Combine enough sampling units to give a weight ofmaterial equal to or greater than the required specimen size.Divide the entire bulk sample into such groups, making all groupsas nearly as possible the same size. Each such group is a laboratorysample. Condition each laboratory sample in accordance with TestMethod D1576.7.6 Proceed from this point as directed in the applicable testmethod.8. Report8.1 State that the specimens were obtained as directed inPractice D2525.9. Keywords9.1 moisture content; sampling; statistics; wool3See, for instance, Hoel, P. G., Introduction to Mathematical Statistics, JohnWiley or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D2525 − 135