Reliabilitas bisa diestimasi ku sababaraha cara nu bisa dikelompokkeun kana dua tipe nyaeta: administrasi-tunggal jeung administrasi-multiple. <!--Metoda Multipleadministrasi-administrationmultiple methodsmerlukeun requiredua thatpeniley twodina assessments are administeredadministrasina. Dina In themetoda ''test-retest'' method, reliabilityreliabiliti isdianggap estimated as thesalaku ''[[Pearson product-moment correlation coefficient]]'' betweenantara twodua administrationsukuran ofadministrasi thenu same measuresarua. Dina In themetoda ''alternate forms'' method, reliabilityreliabiliti isdiitung estimated by themake ''Pearson product-moment correlation coefficient'' oftina twodua differentbentuk forms of anu measurebeda, usuallyilaharna administereddi-administrasi-keun togetherbabarengan. SingleMetoda administrasi-administration methodstunggal includekaasup ''split-half'' andsarta ''internal consistency''. TheMetoda ''split-half'' methodngawengku treatsukuran the twodua ''halves'' ofsalaku abentuk measure as alternate formsalternatipna. Ieu Thisestimasi "halves reliability" estimatesaterusna isdilajuning thenlakukeun steppedku upcara to the full test length using themake ''[[Spearman-Brown prediction formula]]''. The most commonUkuran internal consistencynu ilahar measuredipake isnyaeta [[Cronbach's alpha]], whichnu isilaharna usuallydianggap interpreted as thesalaku [[mean]] ofkeur allsakabeh possiblekoefisien ''split-half coefficients''.
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Each of these estimation methods is sensitive to different sources of error and so might not be expected to be equal. Also, reliability is a property of the ''scores of a measure'' rather than the measure itself and are thus said to be ''sample dependent''. Reliability estimates from one sample might differ from those of a second sample (beyond what might be expected due to sampling variations) if the second sample is drawn from a different population because the true reliability is different in this second population. (This is true of measures of all types--yardsticks might measure houses well yet have poor reliability when used to measure the lengths of insects.)
