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PHNG PHP X L V PHN TCH S LIU NGHIN CU

TS.BS V Bo Dng

X l v phn tch s liu hay d liu nghin cu l mt trong cc bc c bn ca mt nghin cu, bao gm xc nh vn nghin cu; thu thp s liu; x l s liu; phn tch s liu v bo co kt qu. Xc nh r vn nghin cu gip vic thu thp s liu c nhanh chng v chnh xc hn. c c s phn tch s liu tt th trong qu trnh thu thp s liu phi xc nh trc cc yu cu ca phn tch c th thu thp v ng s liu nh mong mun. iu ct li ca phn tch s liu l suy din thng k, ngha l m rng nhng hiu bit t mt mu ngu nhin thnh hiu bit v tng th, hay cn gi l suy din quy np. Mun c c cc suy din ny phi phn tch s liu da vo cc test thng k m bo tin cy ca cc suy din. Bn thn s liu ch l cc s liu th, qua x l phn tch tr thnh thng tin v sau tr thnh tri thc. y chnh l iu m tt c cc nghin cu u mong mun. Trong khun kh ca bi vit ny, tc gi mun trnh by vi ngi c mt s khi nim v k thut c bn khi x l v phn tch s liu. Bn cnh , tc gi gii thiu mt s thao tc c bn khi x l s liu trn phn mm SPSS, mt phn mm x l thng k c s dng nhiu nht hin nay. 1. X l s liu nghin cu Ngy nay, hu ht cc nghin cu u x l s liu trn cc phn mm my tnh. Do vy, vic x l s liu phi qua cc bc sau: - M ha s liu: Cc s liu nh tnh (bin nh tnh) cn c chuyn i (m ha) thnh cc con s. Cc s liu nh lng th khng cn m ha. - Nhp liu: S liu c nhp v lu tr vo file d liu. Cn phi thit k khung file s liu thun tin cho vic nhp liu. - Hiu chnh: L kim tra v pht hin nhng sai st trong qu trnh nhp s liu t bng s liu ghi tay vo file s liu trn my tnh. 2. Phn loi cc s liu (bin s) trong nghin cu C 2 loi bin s chnh trong hu ht cc nghin cu l bin s nh tnh v bin s nh lng. - Bin nh tnh: l loi bin s phn nh tnh cht, s hn km. C th biu din di dng nh danh (v d: nam/n) hay th bc (tt/kh/trung bnh/yu)i vi loi bin s ny ta khng tnh c gi tr trung bnh ca s liu. - Bin nh lng: Thng c biu din bng cc con s. Cc con s ny c th di dng bin thin lin tc (v d: huyt p ca bnh nhn theo thi gian) hoc ri rc (v d: chiu cao, cn nng ca ngi bnh lc vo vin). Dng

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bin ny cho php chng ta tnh c gi tr trung bnh ca bin. Cn lu l tt c cc bin nh lng u phi c n v tnh (mmHg, mmol/L, mg%, Kg) 3. Mt s nguyn tc chn test thng k trong phn tch s liu nghin cu Khi chn mt test thng k cn cn nhc cc yu t sau: - Mc tiu nghin cu: o lng s khc nhau hay mi tng quan gia cc bin s. - S nhm nghin cu: mt nhm, hai nhm hay trn 2 nhm. - C mu nghin cu: nh hay ln. - Bn cht ca s liu, loi bin s: nh tnh hay nh lng. - Phn b mu: phn b chun hay khng chun. - Loi quan st: mu c lp hay ghp cp. C 2 loi test thng k cn bn l test tham s (parametric test) v test phi tham s (non-parametric test). Test tham s ch dng cho cc nghin cu c c mu ln (> 30), phn b ca qun th l phn b chun, thng dng vi cc bin nh lng, cc test thng dng l t test, ANOVA, tng quan Pearson, hi quy tuyn tnh Test phi tham s c th p dng cho cc mu nghin cu ln v nh, phn b ca qun th khng bit c hoc c phn b khng chun, c th dng cho c bin danh mc hoc th hng (nh tnh), cc test thng dng l Fisher test, Median test, 2 test, Kruskal-Wallis one way ANOVA test, tng quan th hng Spearman 4. Phn tch s liu nghin cu 4.1. M t cc bin s - T l: i vi cc bin nh tnh. T t l c th c lng t mu ra qun th nghin cu vi cc php c lng im, c lng khong hoc kim nh gi thuyt cho t l cu mt nhm hay nhiu nhm. - Gi tr trung bnh (X), trung v , lch chun (SD), gi tr ln nht, gi tr nh nht: i vi cc bin nh lng. Tng t nh vi bin nh tnh, t cc gi tr trung bnh ca mu c th c lng im, c lng khong ra cc gi tr ca qun th. 4.2. Phn tch s khc bit - So snh 2 t l. - So snh 3 t l hoc hn. - So snh 2 gi tr trung bnh. - So snh 3 gi tr trung bnh hoc hn. 4.3. Phn tch mi lin quan gia cc bin s - Tng quan gia 2 bin nh tnh:

+ T sut chnh hin mc (POR: Prevalence Odd Ratio): trong nghin cu ngang.

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+ T sut chnh OR: trong nghin cu bnh chng khng ghp cp. + Nguy c tng i RR (Relative Risk): trong nghin cu thun tp.

- Tng quan gia 2 bin nh lng: + H s tng quan r. + Phng trnh hi quy tuyn tnh: Y = a + bX

- Tng quan gia 3 bin nh tnh tr ln: phn tch tng. - Tng quan hi quy tuyn tnh bi 5. Phn tch s liu vi phn mm SPSS: Mt s thao tc c bn

CCH THC TIN HNH LNH FREQUENCIES (Tnh tn s)

1. Sau khi m file d liu, vo menu Analyze Descriptive Statistics Frequencies

Mn hnh s xut hin hp thoi sau:

V biu

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2. Chn bin mun tnh tn s (bin Place V1) bng cch click chut vo tn bin ri a sang khung Variable(s).

3. Click Ok. Trng hp mun v biu thc hin thm bc 4 trc khi click Ok. 4. v biu click chut vo Charts. Chn dng biu Chart type, chn

gi tr th hin trn biu l s m (frequencies) hay phn trm (percentages). Click Continue tr li hp thoi Frequencies Ok thc hin lnh.

TNH TR TRUNG BNH (2 CCH)

CCH 1. DNG LNH FREQUENCY

1. Vo menu Analyze Descriptive Statistics Frequencies. a bin cn tnh tr trung bnh vo variables nh bc 1 v 2 phn trc.

2. Click chn th Statistic, m hp thoi, v click chn cc thng s cn thit:

3. ngha mt s thng s thng dng: Mean: trung bnh cng Sum: tng cng (cng tt c cc gi t trong tp d liu quan st) Std. Deviation: lch chun Minimum: gi tr nh nht Maximum: gi tr ln nht S.E. mean: sai s chun khi c lng tr trung bnh

CCH 2. DNG LNH DESCRIPTIVES (Tnh im trung bnh)

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1. Vo menu Analyze Descriptive Statistics Descriptives, xut hin hp thoi

2. Chn 1 hay nhiu bin (nh lng) mun tnh im trung bnh a vo khung Variable(s).

3. Click vo Options xut hin hp thoi Descriptive Options. Chn cc i lng thng k mun tnh ton bng cch click vo vung cn thit.

4. Chn cch sp xp kt qu tnh ton theo th t danh sch bin (Variable list), th t Alphabetic ca nhn bin, th t tng dn (Ascending list), v th t gim dn (Descending list).

5. Click Continue tr v hp thoi Descriptive Ok thc hin lnh.

CCH THC TIN HNH PHN TCH BNG CHO

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(CROSSTABULATION)

Phn tch bng cho dng kim nh mi quan h gia cc bin nh tnh vi nhau bng cch dng kim nh Chi bnh phng (Chi-square). Cch thc tin hnh vi SPSS nh sau:

1. Vo menu Analyze Descriptive Statistics Crosstabs,

2. Xut hin hp thoi sau:

3. Chn v a cc bin vo khung Row(s) (dng) v Column(s) (ct) v Layer 1 of 1 (i vi trng hp trn 2 bin).

4. Click vo Statistics, xut hin hp thoi sau:

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5. Chn cc kim nh cn thit. Trong trng hp ny ta dng kim nh Chi bnh phng (Chi-square). - Cc kim nh Norminal dng kim nh mi lin h gia cc bin biu

danh. - Cc kim nh Ordinal dng kim nh mi lin h gia cc bin th t.

6. Click vo continue tr li hp thoi Crosstabs Click vo Cells, hp thoi sau xut hin:

7. Counts chn Observed (th hin tn s quan st). Trong

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trng hp mun th hin tn s mong i chn Expected. 8. Chn cch th hin phn trm theo dng hay theo ct Percentages. 9. Click Continue tr li hp thoi Crosstabs Ok thc hin lnh.

CCH C KT QU KIM NH

Khi thc hin kim nh, ta c 2 gi thuyt. H0: khng c mi quan h gia cc bin. H1: c mi quan h gia cc bin.

kt lun l chp nhn hay bc b gi thuyt H0, ta s dng cc kim nh ph hp. Da vo gi tr P (p-value) (SPSS vit tt p-value l sig.) kt lun l chp nhn hay bc b gi thuyt H0

p-value (sig.) (mc ngha) bc b gi thuyt H0. C ngha l c mi quan h c ngha gia cc bin cn kim nh. p-value (sig.) > (mc ngha) chp nhn H0. Khng c mi quan h gia cc bin cn kim nh.

I VI KIM NH CHI BNH PHNG Hng u tin ca bng Chi-square tests th hin gi tr P

Chi-Square Tests

Value df Asymp. Sig. (2-sided)

Pearson Chi-Square 16.217a 8 .039

Likelihood Ratio 18.708 8 .017

Linear-by-Linear Association .202 1 .653

N of Valid Cases 511

a. 8 cells (44.4%) have expected count less than 5. The minimum expected count is 1.69.

Cui bng Chi-Square tests SPSS s a ra dng thng bo cho bit % s c tn sut mong i di 5. Kim nh Chi-bnh phng ch c ngha khi s quan st ln, nu c qu 20% s trong bng cho c tn s l thuyt nh hn 5 th gi tr chi-bnh phng khng cn ng tin cy.

Trong v d trn c n 44.4% s c tn s mong i di 5, bin php cho trng hp ny l ta s gom cc biu hin trn cc bin li tng s quan st trong mi nhm.

p-value

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CCH THC TIN HNH KIM NH GI THUYT V TR TRUNG BNH CA 2 TNG TH C LP (Independent Samples T-test)

1. Vo menu Analyze Compare Means Independent-samples T-test

2. Chn bin nh lng cn kim nh tr trung bnh a vo khung Test Variable(s). Chn bin nh tnh chia s quan st thnh 2 nhm mu so snh gia 2 nhm ny vi nhau a vo khung Grouping Variable.

3. Chn Define Groups nhp m s ca 2 nhm. Click Continue tr li hp thoi chnh Click Ok thc hin lnh

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Trong kim nh Independent-samples T-test, ta cn da vo kt qu kim nh s bng nhau ca 2 phng sai tng th (kim nh Levene). Phng sai din t mc ng u hoc khng ng u ( phn tn) ca d liu quan st.

Independent Samples Test

A.Cleanliness and comfort of room

Equal variances

assumed

Equal

variances not

assumed

F .138 Levene's Test for Equality of

Variances Sig. .710

t -3.066 -3.040

df 509 448.100

Sig. (2-tailed) .002 .003

Mean Difference -.231 -.231

Std. Error Difference .075 .076

Lower -.379 -.380

t-test for Equality of Means

95% Confidence Interval

of the Difference Upper -.083 -.082

Nu gi tr Sig. trong kim nh Levene (kim nh F) < 0.05 th phng sai ca 2 tng th khc nhau, ta s dng kt qu kim nh t dng Equal variances not assumed. Nu Sig. 0.05 th phng sai ca 2 tng th khng khc nhau, ta s dng kt qu kim nh t dng Equal variances assumed. Trong VD trn Sig. ca kim nh F = 0.71 > 0.05 chp nhn gi thuyt H0 khng c s khc nhau v phng sai ca 2 tng th s dng kt qu dng Equal variances assumed. Nu Sig. ca kim nh t (mc ngha) c s phc bit c ngha v trung bnh ca 2 tng th. Nu Sig. > (mc ngha) khng c s khc bit c ngha v trung bnh ca 2 tng th. Trong VD trn sig. = 0.002 < 0.05 c s khc bit c ngha v trung bnh ca 2 tng th.

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CCH THC TIN HNH PHN TCH PHNG SAI (ANOVA Analysis of Variance)

Phn tch phng sai ANOVA l phng php so snh tr trung bnh ca 3 nhm

tr ln. C 2 k thut phn tch phng sai: ANOVA 1 yu t (mt bin yu t phn loi cc quan st thnh cc nhm khc nhau) v ANOVA nhiu yu t(2 hay nhiu bin phn loi). phn thc hnh c bn ch cp n phn tch phng sai 1 yu t (One-way ANOVA).

Mt s gi nh i vi phn tch phng sai mt yu t: - Cc nhm so snh phi c lp v c chn mt cch ngu nhin. - Cc nhm so snh phi c phn phi chun hoc c mu phi ln c

xem nh tim cn phn phi chun. - Phng sai ca cc nhm so snh phi ng nht.

1. T menu Analyze Compare Means One-Way ANOVA, xut hin hp thoi sau:

2. a bin nh lng (tr trung bnh) vo khung Dependent list. a bin phn loi xc nh cc nhm cn so snh vi nhau vo khung Factor.

3. Click vo nt Option m hp thoi One-Way ANOVA Options. Trong hp thoi One-way ANOVA Options: - Click chn Descriptive tnh i lng thng k m t (tnh tr trung bnh)

theo tng nhm so snh. - Click chn Homogeneity of variance test kim nh s bng nhau ca cc

phng sai nhm (thc hin kim nh Levene).

2 k thut dng

kim nh su ANOVA

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4. Click chn Continue tr li hp thoi ban u click Ok thc hin lnh.

5. Da vo kt qu kim nh ANOVA, nu H0 c chp nhn th kt lun khng c s khc bit c ngha gia cc nhm vi nhau. Nu H0 b bc b c s khc bit c ngha gia cc nhm tr li hp thoi One way ANOVA thc hin kim nh su ANOVA nhm xc nh c th trung bnh ca nhm no khc vi nhm no, ngha l tm xem s khc bit ca cc nhm xy ra u.

6. Tuy nhin c th thc hin kim nh ANOVA v su ANOVA cng lc vi nhau. Da vo s chp nhn hay bc b gi thuyt H0 quan tm hay khng quan tm n kt qu kim nh su ANOVA.

Ti liu tham kho:

1. Hm (2009), Phng php lun trong nghin cu khoa hc y hc, Trng i hc Y khoa Thi Nguyn. 2. Phm Vn Hin (2009), Phng php tip cn nghin cu khoa hc, http://pgo.hcmuaf.edu.vn/pvhien. 3. Nguyn Vn H, Nguyn ng Bnh (2004), Phng php lun nghin cu khoa hc, i hc Thi Nguyn. 4. inh Thanh Hu (2004), Phng php nghin cu khoa hc, Trng i hc Y Hu. 5. Hong Trng, Chu Nguyn Mng Ngc (2008), Phn tch d liu nghin cu vi SPSS, Trng i hc Kinh t TP H Ch Minh. 6. Nguyn Vn Tun (2009), Phng php nghin cu khoa hc gio dc, Trng i hc SPKT TPHCM.