3.4.3 Non-okungenzeka amasampula: sample elihamelanayo

Akuzona zonke amasampula non-ematfuba ziyafana. Singasho wengeze control more on the front end.

Le ndlela Wang nozakwabo esetshenziswa ukulinganisa umphumela we-2012 US ngokhetho kwakuxhomeka ukuthuthuka ukuhlaziya idatha. Okungukuthi, babuthela izimpendulo eziningi njengoba bangahle kwalokho wazama ukuba kabusha isisindo kubo. Kumele kuqhanyukwe nesu aphelele ngokusebenzisana non-ematfuba ukusampula ukulawula inqubo iqoqo idatha.

Isibonelo elula a ivele kancane elawulwa non-ematfuba ukusampula nqubo quota izibonelo zalokho, inqubo lusukela ekuqaleni ucwaningo inhlolovo. Ngo-quota izibonelo zalokho, abacwaningi bahlukanise inani labantu babe ngamaqembu ahlukene (isib, izinsizwa, abesifazane abasebasha, njll) bese isethi quota for isibalo sabantu okumele kukhethwe ecenjini ngalinye. Esakhuluma Abazinikele bakhethwa ngendlela ozenzekelayo kuze kube umcwaningi uye wahlangana quota zabo esiqhemeni ngasinye. Ngenxa izabelo, isampula kwaphumela ubukeka more like labantu target kuka kuyoba njalo ngenye indlela, kodwa ngoba kwenzeke of iinthombe awaziwa abacwaningi abaningi bayangabaza quota sampling. Empeleni, quota ukusampula kwaba imbangela "Dewey unqoba Truman" iphutha 1948 US Presidential ngezinhloko. Nokho, Ngoba inikeza ngezinga elithile inqubo izibonelo zalokho, umuntu angabona ukuthi quota izibonelo zalokho okungenzeka babe izinzuzo ezithile engaphezu engalawuliwe ngokuphelele iqoqo idatha.

Ukuthuthela ngaphesheya quota izibonelo zalokho, tindlelanchubo zanamuhla ukulawula non-ematfuba izibonelo zalokho inqubo manje kungenzeka. Enye indlela enjalo yokuhlaziya isimo ubizwa ngokuthi isampula elimetjhako, futhi isetshenziswa abanye commercial online panel abahlinzeki. In injalo elula, isampula lelihambisana kudinga imithombo emibili idatha: 1) irejista ephelele wabantu 2) panel enkulu amavolontiya. Kubalulekile ukuthi izisebenzi zokuzithandela akudingeki ukuba ube isampula Amathuba kusuka kunoma iyiphi labantu; ukuze agcizelele ukuthi azikho izidingo yokukhethwa ephaneleni, ngizobuya call it a panel singcolile. Futhi, kokubili irejista labantu kanye panel ezingcolile kufanele eminye imininingwane asizayo ngomuntu ngamunye, kulesi sibonelo, ngizobuya cabanga yobudala kanye ocansini, kodwa ezimweni namaqiniso lolu lwazi asizayo kungaba enemininingwane okuningi. The trick isampula lelihambisana iwukukhetha amasampula kusuka panel angcolile ngendlela eyenza imiklamo amasampula ukuthi ibukeke amasampula ematfuba.

Sample elimetjhako iqala lapho eyenziwe Amathuba isampula othathwe irejista labantu; lokhu isampula eyenziwe iba isampula target. Khona-ke, esekelwe ulwazi asizayo, emacaleni isampula target abafanelana abantu kwephaneli ezingcolile ukwakha isampula abafanelana. Ngokwesibonelo, uma kukhona female ngonyaka 25 ubudala isampula target, khona-ke umcwaningi uthola female ngonyaka 25 ubudala kusukela panel ezingcolile ukuba khona isampula abafanelana. Ekugcineni, amalungu isampula ifaniswe Kuxoxwa ukuze aveze isethi yokugcina wabaphenduli.

Nakuba isampula ifaniswe libukeka isampuli target, kubalulekile ukukhumbula ukuthi isampula ifaniswe akuyona isampula ematfuba. Amasampula Usisiza kungaba kuphela umadanise isampula target ulwazi asizayo eyaziwa (isib, yobudala kanye ocansini), kodwa hhayi on izici unmeasured. Ngokwesibonelo, uma abantu panel ezingcolile bathambekele empofu-phela esinye sezizathu ukuthi ujoyine i-panel inhlolovo ukuthola imali-ke ngisho noma isampula ifaniswe libukeka isampula target ngekweminyaka yebudzala and sex isazoba a noma ukuchema kuzo ngabantu abampofu. The magic of weqiniso ematfuba ukusampula siqambe izinkinga kokubili izici alinganiswe futhi unmeasured (iphuzu okuhambisana ingxoxo yethu afanayo for nikhuluma esiyimbangela ezifundweni elibukelayo eSahlukweni 2).

Ngo practice, isampula lelihambisana ixhomeke ekubeni panel enkulu futhi ezihlukahlukene ababezimisele, ukuba bakwazi ukuqedela survey, futhi ngaleyo ndlela ibizwa isikakhulukazi yizinkampani engakwazi ukuthola lokho ikwenze sihlakulele futhi silondoloze panel enjalo. Futhi, umkhuba, kungaba khona izinkinga ne lelihambisana (ngezinye izikhathi nomdlalo omuhle kumuntu isampula target ayikho panel) kanye non-Ukusabela (ngezinye izikhathi abantu isampula ifaniswe ayenqaba ukuhlanganyela kulolu cwaningo). Ngakho-ke, ngo umkhuba, abacwaningi ukwenza isampula elimetjhako futhi enze okuthile post-babhekane nezinga elikhulu ukulungiswa ukuba basho lezo zilinganiso.

Kunzima ukunikeza iziqiniseko ewusizo theory mayelana isampula elimetjhako, kodwa empeleni kungaba enze kahle. Ngokwesibonelo, uStefanu Ansolabehere Brian Schaffner (2014) uma kuqhathaniswa survey ezintathu ezifanayo njengoba abantu abalinganiselwa ku-1000 olwenziwa ngo-2010 ngokusebenzisa ezintathu izibonelo zalokho ezahlukene kanye kokuxoxa izindlela: mail, ucingo, nethimba Inthanethi ngokusebenzisa isampula elimetjhako nangemuva babhekane nezinga elikhulu ukulungiswa. I ezakhishwa izindlela ezintathu zazingabantu iyafana ezakhishwa eliphezulu zokubekisa ezifana Current Population Survey (CPS) kanye Interview National Health Survey (NHIS). Ngini ngokuqondile, kokubili e-inthan bese mail survey baba ngamashumi off nge-avareji ka-3 ngemaphesenti kanye inhlolovo Ifoni off by 4 ngemaphesenti. Amaphutha lokhu enkulu kwakuyoba cishe lokho omunye alindele kusukela amasampula abantu mayelana 1,000. Nakuba, ayikho kulezi zindlela kwaveza idatha kakhulu kangcono, kokubili Internet kanye nefoni inhlolovo (okwakuthatha izinsuku noma amasonto) ngamashumi kakhulu ngokushesha waya ensimini ukwedlula imeyili inhlolovo (okwakuthatha izinyanga eziyisishiyagalombili), kanye vo ye-Internet, okuyinto esetshenziswa isampula elimetjhako: kwaba ushibhile ukwedlula ezinye izindlela ezimbili.

Ekuphetheni, ososayensi bezenhlalo futhi labantu ngendlela emangalisayo uyangabaza okucatshangwayo kusukela masampuli non-okungenzeka, ngokwengxenye ngoba zihlotshaniswa nesimo sokwehluleka amahloni ucwaningo inhlolovo ezifana Literary Digest poll. Ngokwengxenye, mina ngivumelana nale zokungabaza: non-okungenzeka amasampula engalungisiwe kukhona cishe ukukhiqiza tilinganiso ezimbi. Nokho, uma abacwaningi ulungise for ukucwasana kule nqubo izibonelo zalokho (isib, post-babhekane nezinga elikhulu) noma ukulawula inqubo izibonelo zalokho Kuthi (isib, isampula kumatanisa), abakwazi ukukhiqiza tilinganiso kangcono, futhi ngisho izilinganiso izinga ezanele ngezinhloso kakhulu. Yiqiniso, kungaba ngcono ukuba benze ababulawa ngokuphelele ematfuba izibonelo zalokho, kodwa ukuthi ubonakala ayisekho ukuba ube option namaqiniso.

Bobabili amasampula non-okungenzeka kanye amasampula ematfuba ziyehluka izinga kwabo, futhi okwamanje kungenzeka icala lokuthi tilinganiso kakhulu kusukela amasampula okungenzeka kukhona ithembeke ngaphezu kwanoma ezakhishwa amasampula non-ematfuba. Kodwa, ngisho namanje, ezakhishwa non-okungenzeka amasampula esiqhutshwa kahle cishe kangcono ukwedlula ezakhishwa okungenzeka amasampula ekhanya-olwenziwe. Ngaphezu kwalokho, amasampula non-okungenzeka ishibhile kakhulu. Ngakho, kubonakala sengathi ematfuba vs non-okungenzeka izibonelo zalokho inikeza izindleko-quality ukuhweba (Figure 3.6). Uma sibheka phambili, ngilindele ukuthi ezakhishwa non-okungenzeka amasampula kahle kwenziwe iyoba eshibhile futhi ezingcono. Ngaphezu kwalokho, ngenxa ukuwohloka kwezindinganiso ninalo ucingo survey kanye amazinga elandayo lezisebenzi non-Ukusabela, ngilindele ukuthi amasampula ematfuba iyoba ezibizayo futhi kusezingeni aphansi. Ngenxa yalezi zimpikiswano yesikhathi eside, ngicabanga ukuthi non-okungenzeka izibonelo zalokho iyoba nakakhulu ngenkathi yesithathu yocwaningo inhlolovo.

Figure 3.6: Amathuba izibonelo zalokho practice and non-okungenzeka izibonelo zalokho kukhona kokubili, izigaba ezinkulu heterogeneous. Ngokuvamile, kukhona izindleko-iphutha ukuhweba-off ne non-ematfuba izibonelo zalokho kokuba nezindleko eziphansi kodwa iphutha ephakeme. Nokho, kuhle kwenziwe non-okungenzeka izibonelo zalokho ungaveza tilinganiso kangcono kunokuba ekhanya kwenziwe ematfuba sampling. Esikhathini esizayo, ngilindele ukuthi non-okungenzeka izibonelo zalokho uyothola kangcono futhi ashibhile kanti ematfuba izibonelo zalokho izoba buhlungu nakakhulu futhi ezibizayo.