Which Statistical Method to Use

8/6/2019 Which Statistical Method to Use

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Test Number of groups Data type

T-test 2 groups Numerical

ANOVA 3 or more groups Numerical

Binomial Test 2 groups Binary

Chi-square 2 groups Categorical

Which statistical method to use?



If you have two variables (numerical)You want to compare if the two means of

the two variables is statistical different

For between subjects experimentUse Independent samples t-test

For within subjects experimentUse Paired-samples t-test

T-test



Paired-samples t-test

A paired-samples t-test was conducted to

compare variable 1 in condition 1 and condition 2.There was no significant difference in the score of

variable 1 for condition 1 (M= 52.2, SD=10.25) andcondition 2 (M= 52.8, SD= 9.48); t(199)=-.87 ,p=0.387 .



Independent samples t-test

There are two Sig.Check out the Sig. of Levene’s Test firstIf Sig. of Levene’s Test < 0.05Use the Sig. of “Equal variance not assumed”

If Sig. of Levene’s Test > 0.05

Use the Sig. of “Equal variance assumed”



An independent samples t-test was conducted tocompare variable 1 in condition 1 and condition 2.There was a significant difference in the score of

variable 1 for condition 1 (M= 52.2, SD=10.25) andcondition 2 (M= 52.8, SD= 9.48); t(169.71)=-3.656,

p=0.000.

Independent samples t-test



If you have more than two variables (numerical)You want to compare if the means of the

variables is statistical different

Use ANOVA!

ANOVA



SPSS – Between Subjects ANOVA

A one-way between subjects ANOVA wasconducted to compare variable 1 in condition 1,

condition 2 and condition 3.There was a significant difference of variable 1 on

variable 2 at the p<.05 level for the N conditions

[F(2,12)=4.94, p=0.027 ].



Problem: When Sig. < .05, there exists an effectbetween the some of the conditions, but we donot know specifically between which condition(s)

E.g. If we have 3 conditions, and Sig. <.05Effect between 1&2, no effect between 1&3; 2&3Effect between 1&3, no effect between 1&2; 2&3Effect between 2&3, no effect between 1&2; 1&3Effect between 1&2; 2&3, no effect between 1&3Effect between 1&3; 2&3, no effect between 1&2Effect between 1&2; 2&3, no effect between 1&3





Post-hoc test

Post hoc comparisons using Tukey HSD test indicated

that the mean score for condition 1 (M=4.20, SD=1.30)was significantly different than condition 3. However,condition 2 (M= 3.60, SD=0.89) did not significantly

differ from condition 1 and condition 3.



A one-way withinsubject ANOVAwas conducted tocompare theeffect of DV on IV in condition 1, condition 2 andcondition 3. There was a significant effect of the IV ,

Wilks’ Lambda=0.10, F(2,3)=13.42, p=.032.

SPSS – Within Subjects ANOVA



Perform post hoc paired-sample t-test for eachpair of conditionsIf you have 3 conditions

• T-test #1 for condition 1&2• T-test #2 for condition 1&3• T-test #3 for condition 2&3

For test of significance,Use Sig. Value of .05 / # of test

• For 3 conditions, .05/3 = .017• For 4 conditions (6 post hoc tests), .05/6 = .008

Follow the aired-sam le t-test rocedure...

SPSS – Post hoc paired-samples t-test



For binary variables (Yes, No)E.g. Prospect Theory

• You have 2 identical choice

• You want to show a bias in making choicei.e. people tend to make one choice than the

other, even though the choices are identical•

H0: No bias in choice – 50/50 in the twoconditions

• H1: Bias in choice – not 50/50 in the twoconditions

Binomial Test



Sig. < .05Reject H0i.e. There exists a bias in choice

SPSS - Binomial Test



Two categorical variables [Yes, No] [Male, Female]See if there is a relation between the two variablesUse Chi-Square Test

H0: No relation between the two variablesH1: There exists a relation between the two

variables

Reject H0 is p<.05i.e. there exist a significant effect between the

two variables

Chi-Square Test



Sig. > .05Reject H1i.e. There is no bias

in choice betweenmale and female.

The percentage of participants that wererepublican ordemocrat did notdiffer by gender,

χ2(1, N=12)=0.00, p=1.00.

SPSS –Chi-Square

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Which Statistical Method to Use