MCF - LabPsy - Université de Bordeaux
IE - LabPsy - Université de Bordeaux
Echantillons
Un petit échantillon, qu’est-ce que c’est ?


Petits échantillons, dans nos pratiques
Etude d’Avezier et al. 2012 - 45 participants


- 45 participants - étude initiale - Avezier et al. en 2012 – Science ;
- 14 participants - réplication en 2018 - Camerer et al. – Nature ;
- 24 participants - réplication en 2023, Holzmeister et al. - Pre-data Collection Replication Report, OSF ;
- 194 participants - réplication de N. Pillaud en 2025 - Pillaud et al. 2025 – Emotion ;
- Réplication en live - une journée d’études - Université de Bordeaux : 62 membres de l’ESR;
-> Qu’est-ce qu’un petit nombre ? de 14 participants à 194 l’effet reste stable
Implication de la taille d’effet
- la plus petite taille d’effet rapportée dans l’étude initiale est de :
- \(\eta^2_p\) = 0.74
=
- \(d\) = 3.37
Probabilité de trouver un effet s’il existe
- J. Neyman & E. Pearson - 1933
- J. Cohen - 1962, 1988
- …
| Rejet de \(H_0\) | Non-rejet de \(H_0\) | |
|---|---|---|
| \(H_0\) correcte | Erreur de Type I (\(\alpha\)) | Décision correcte (\(1 - \alpha\)) |
| \(H_0\) incorrecte | Décision correcte (\(1 - \beta\)) | Erreur de Type II (\(\beta\)) |

On en utilise tout le temps en SHS :
\[ d = \frac{|mA - mB|}{SD_{pooled}}\]
- \(d\) de Cohen : indice de taille d’effet pour échantillons indépendants.
- \(mA\) & \(mB\) : sont les moyennes des groupes \(A\) et \(B\).
\[SD_{pooled} = \sqrt {\frac {\sum{(x - mA)^2} + \sum{(x - mB)^2}}{nA + nB - 2}}\]
Avec \(mA\) & \(mB\), les moyennes des groupes \(A\) et \(B\) et \(nA\) & \(nB\) les effectifs des groupes A et B.
\[ \eta_p^2 = \frac {t^2}{t^2 + (nA + nB - 2)}\] - \(\eta_p^2\) : indice de taille d’effet pour échantillons indépendants.
- \(t\) : indice statistique du test \(t\) (aussi appelé \(t\) de Student).
- \(nA\) & \(nB\) : effectifs des groupes A et B.
\[ V = \sqrt {\frac{\chi^2}{n * k}} \]
- \(V\) : indice de taille d’effet pour 2 variables catégorielles à plusieurs modalités.
- \(\chi^2\) : indice statistique du test du \(\chi^2\).
- \(n\) : échantillon total.
- \(k\) : le plus petit nombre, soit de lignes, soit de colonnes, de la table de contingence.
Test du \(khi²\) et taille d’effet (\(V\) de Cramer)
Fréquence de visite de sa mère biologique et le fait d’être au chômage
Pearson's Chi-squared test
data: chi2
X-squared = 34.423, df = 3, p-value = 1.613e-07
[1] 0.07695327
+--------------------------------------------------+
| POWER CALCULATION |
+--------------------------------------------------+
Generic Chi-square Test
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : ncp = null.ncp
H1 (Alt. Claim) : ncp > null.ncp
---------------------------------------------------
Results
---------------------------------------------------
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.000
Statistical Power = 1 <<
L’exemple précédent portait sur 5813 observations.
Calcul de puissance a priori
+--------------------------------------------------+
| SAMPLE SIZE CALCULATION |
+--------------------------------------------------+
Chi-Square Test for Goodness-of-Fit or Independence
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : P[i,j] = P0[i,j] for all (i,j)
H1 (Alt. Claim) : P[i,j] != P0[i,j] for some (i,j)
---------------------------------------------------
Results
---------------------------------------------------
Total Sample Size = 1844 <<
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.200
Statistical Power = 0.8
Différents modèles, différents algorithmes
Test t et taille d’effet (\(d\) de Cohen) Satisfaction de la répartition des tâches ménagères comparaison hommes/femmes parmi les agriculteurs
Two Sample t-test
data: DF_agri$OA_SATREP by DF_agri$MA_SEXE
t = 2.3735, df = 92, p-value = 0.0197
alternative hypothesis: true difference in means between group 1 and group 2 is not equal to 0
95 percent confidence interval:
0.1256708 1.4141843
sample estimates:
mean in group 1 mean in group 2
8.291667 7.521739
Call: cohen.d(x = DF_agri$OA_SATREP, group = DF_agri$MA_SEXE)
Cohen d statistic of difference between two means
lower effect upper
[1,] -0.9 -0.5 -0.08
Multivariate (Mahalanobis) distance between groups
[1] 0.5
r equivalent of difference between two means
data
-0.24
Calcul de puissance a priori
power.t.student(d = -0.5,
power = 0.80,
alpha = 0.05,
alternative = "two.sided",
design = "independent")+--------------------------------------------------+
| SAMPLE SIZE CALCULATION |
+--------------------------------------------------+
Student's T-Test (Independent Samples)
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : d - null.d = 0
H1 (Alt. Claim) : d - null.d != 0
---------------------------------------------------
Results
---------------------------------------------------
Sample Size = 64 and 64 <<
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.199
Statistical Power = 0.801
Calcul de puissance a posteriori
+--------------------------------------------------+
| POWER CALCULATION |
+--------------------------------------------------+
Generic T-Test
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : ncp = null.ncp
H1 (Alt. Claim) : ncp != null.ncp
---------------------------------------------------
Results
---------------------------------------------------
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.349
Statistical Power = 0.651 <<

Test t et taille d’effet (\(d\) de Cohen) Satisfaction de la répartition des tâches ménagères selon la présence ou l’absence d’enfant de moins de 14ans dans le ménage, parmi les femmes
Two Sample t-test
data: DF_500f$OA_SATREP by DF_500f$NBENF14_rec
t = -0.21736, df = 498, p-value = 0.828
alternative hypothesis: true difference in means between group 1 and group 2 is not equal to 0
95 percent confidence interval:
-0.3816300 0.3056018
sample estimates:
mean in group 1 mean in group 2
7.864583 7.902597
Call: cohen.d(x = DF_500f$OA_SATREP, group = DF_500f$NBENF14_rec)
Cohen d statistic of difference between two means
lower effect upper
[1,] -0.16 0.02 0.2
Multivariate (Mahalanobis) distance between groups
[1] 0.02
r equivalent of difference between two means
data
0.01
Calcul de puissance a priori
power.t.student(d = 0.02,
power = 0.80,
alpha = 0.05,
alternative = "two.sided",
design = "independent")+--------------------------------------------------+
| SAMPLE SIZE CALCULATION |
+--------------------------------------------------+
Student's T-Test (Independent Samples)
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : d - null.d = 0
H1 (Alt. Claim) : d - null.d != 0
---------------------------------------------------
Results
---------------------------------------------------
Sample Size = 39246 and 39246 <<
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.200
Statistical Power = 0.8
Calcul de puissance a posteriori
+--------------------------------------------------+
| POWER CALCULATION |
+--------------------------------------------------+
Generic T-Test
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : ncp = null.ncp
H1 (Alt. Claim) : ncp != null.ncp
---------------------------------------------------
Results
---------------------------------------------------
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.945
Statistical Power = 0.055 <<

Test t et taille d’effet (\(d\) de Cohen)
Two Sample t-test
data: DF_f$OA_SATREP by DF_f$NBENF14_rec
t = -2.8853, df = 3263, p-value = 0.003937
alternative hypothesis: true difference in means between group 1 and group 2 is not equal to 0
95 percent confidence interval:
-0.33378601 -0.06368395
sample estimates:
mean in group 1 mean in group 2
7.729233 7.927968
Call: cohen.d(x = DF_f$OA_SATREP, group = DF_f$NBENF14_rec)
Cohen d statistic of difference between two means
lower effect upper
[1,] 0.03 0.1 0.17
Multivariate (Mahalanobis) distance between groups
[1] 0.1
r equivalent of difference between two means
data
0.05
Calcul de puissance a priori
power.t.student(d = 0.1,
power = 0.80,
alpha = 0.05,
alternative = "two.sided",
design = "independent")+--------------------------------------------------+
| SAMPLE SIZE CALCULATION |
+--------------------------------------------------+
Student's T-Test (Independent Samples)
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : d - null.d = 0
H1 (Alt. Claim) : d - null.d != 0
---------------------------------------------------
Results
---------------------------------------------------
Sample Size = 1571 and 1571 <<
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.200
Statistical Power = 0.8
Calcul de puissance a posteriori
+--------------------------------------------------+
| POWER CALCULATION |
+--------------------------------------------------+
Generic T-Test
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : ncp = null.ncp
H1 (Alt. Claim) : ncp != null.ncp
---------------------------------------------------
Results
---------------------------------------------------
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.178
Statistical Power = 0.822 <<

500obs, effet non significatif (p>0.05), \(d\) = 0.02, \(Power\) = 0.06
3265obs, effet significatif (p<0.05), \(d\) = 0.1, \(Power\) = 0.82
Test du \(khi²\) et taille d’effet (\(V\) de Cramer) Comparaison des réponses homme/femme sur l’aide aux devoirs
Calcul de puissance a priori
+--------------------------------------------------+
| SAMPLE SIZE CALCULATION |
+--------------------------------------------------+
Chi-Square Test for Goodness-of-Fit or Independence
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : P[i,j] = P0[i,j] for all (i,j)
H1 (Alt. Claim) : P[i,j] != P0[i,j] for some (i,j)
---------------------------------------------------
Results
---------------------------------------------------
Total Sample Size = 50 <<
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.193
Statistical Power = 0.807
Calcul de puissance a posteriori
+--------------------------------------------------+
| POWER CALCULATION |
+--------------------------------------------------+
Generic Chi-square Test
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : ncp = null.ncp
H1 (Alt. Claim) : ncp > null.ncp
---------------------------------------------------
Results
---------------------------------------------------
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.000
Statistical Power = 1 <<

Modèle de régression linéaire
===============================================
Dependent variable:
---------------------------
OB_DEDUC
-----------------------------------------------
MA_SEXE)2 -0.338***
(0.023)
MA_AGEM_rec -0.001
(0.001)
AH_CS8)3 -0.008
(0.052)
AH_CS8)4 -0.004
(0.048)
AH_CS8)5 -0.027
(0.049)
AH_CS8)6 0.002
(0.049)
AH_CS8)7 -0.040
(0.071)
AH_CS8)8 -0.114**
(0.056)
Constant 3.169***
(0.069)
-----------------------------------------------
Observations 2,959
R2 0.104
Adjusted R2 0.102
Residual Std. Error 0.533 (df = 2950)
F Statistic 42.910*** (df = 8; 2950)
===============================================
Note: *p<0.1; **p<0.05; ***p<0.01
Call:
lm(formula = DFp$OB_DEDUC ~ factor(DFp$MA_SEXE) + DFp$MA_AGEM_rec +
factor(DFp$AH_CS8))
Standardized Coefficients::
(Intercept) factor(DFp$MA_SEXE)2 DFp$MA_AGEM_rec
NA -0.299676843 -0.008885231
factor(DFp$AH_CS8)3 factor(DFp$AH_CS8)4 factor(DFp$AH_CS8)5
-0.004340916 -0.003093925 -0.020698836
factor(DFp$AH_CS8)6 factor(DFp$AH_CS8)7 factor(DFp$AH_CS8)8
0.001123818 -0.013410187 -0.058553337
Puissance a priori sur l’ensemble du modèle
+--------------------------------------------------+
| SAMPLE SIZE CALCULATION |
+--------------------------------------------------+
Linear Regression (F-Test)
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : R-squared = 0
H1 (Alt. Claim) : R-squared > 0
---------------------------------------------------
Results
---------------------------------------------------
Sample Size = 141 <<
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.197
Statistical Power = 0.803
Puissance a posteriori
+--------------------------------------------------+
| POWER CALCULATION |
+--------------------------------------------------+
Linear Regression (F-Test)
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : R-squared = 0
H1 (Alt. Claim) : R-squared > 0
---------------------------------------------------
Results
---------------------------------------------------
Sample Size = 2959
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.000
Statistical Power = 1 <<
Puissance a priori pour une variable
+--------------------------------------------------+
| SAMPLE SIZE CALCULATION |
+--------------------------------------------------+
Linear Regression Coefficient (T-Test)
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : beta - null.beta = 0
H1 (Alt. Claim) : beta - null.beta != 0
---------------------------------------------------
Results
---------------------------------------------------
Sample Size = 81 <<
Type 1 Error (alpha) = 0.050
Type 2 Error = 0.198
Statistical Power = 0.802
Puissance a posteriori pour une variable
+--------------------------------------------------+
| POWER CALCULATION |
+--------------------------------------------------+
Linear Regression Coefficient (T-Test)
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : beta - null.beta = 0
H1 (Alt. Claim) : beta - null.beta != 0
---------------------------------------------------
Results
---------------------------------------------------
Sample Size = 2959
Type 1 Error (alpha) = 0.050
Type 2 Error = 0.000
Statistical Power = 1 <<
Coefficients pour niveau diplôme >BAC+2
| Coefficients standardisés & Odds Ratios | ||||
|---|---|---|---|---|
| Parameter | Std_Odds_Ratio | CI | CI_low | CI_high |
| (Intercept) | 12.353 | 0.950 | 5.137 | 32.531 |
| MA_AGEM_rec | 0.656 | 0.950 | 0.467 | 0.914 |
| MA_SEXE2 | 0.006 | 0.950 | 0.003 | 0.014 |
| MC_DIPLOME2 | 0.898 | 0.950 | 0.172 | 4.997 |
| MC_DIPLOME3 | 0.078 | 0.950 | 0.012 | 0.438 |
| MC_DIPLOME4 | 0.490 | 0.950 | 0.180 | 1.274 |
| MC_DIPLOME5 | 0.285 | 0.950 | 0.058 | 1.331 |
| MC_DIPLOME6 | 0.221 | 0.950 | 0.019 | 1.634 |
| MC_DIPLOME7 | 0.478 | 0.950 | 0.092 | 2.225 |
| MC_DIPLOME8 | 0.293 | 0.950 | 0.085 | 0.973 |
Taille d’effet pour niveau diplôme >BAC+2
Puissance a priori pour niveau diplôme >BAC+2
power.z.logistic(odds.ratio = 0.29,
base.prob = 0.925,
r.squared.predictor = 0.589,
power = 0.80,
alpha = 0.05,
alternative = "two.sided",
distribution = "normal")+--------------------------------------------------+
| SAMPLE SIZE CALCULATION |
+--------------------------------------------------+
Logistic Regression Coefficient (Wald's Z-Test)
Method : Demidenko (Variance Corrected)
Predictor Dist. : Normal
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : Odds Ratio = 1
H1 (Alt. Claim) : Odds Ratio != 1
---------------------------------------------------
Results
---------------------------------------------------
Sample Size = 173 <<
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.199
Statistical Power = 0.801
Puissance a posteriori pour niveau diplôme >BAC+2
power.z.logistic(odds.ratio = 0.29,
base.prob = 0.925,
r.squared.predictor = 0.589,
n = 471,
alpha = 0.05,
alternative = "two.sided",
distribution = "normal")+--------------------------------------------------+
| POWER CALCULATION |
+--------------------------------------------------+
Logistic Regression Coefficient (Wald's Z-Test)
Method : Demidenko (Variance Corrected)
Predictor Dist. : Normal
---------------------------------------------------
Hypotheses
---------------------------------------------------
H0 (Null Claim) : Odds Ratio = 1
H1 (Alt. Claim) : Odds Ratio != 1
---------------------------------------------------
Results
---------------------------------------------------
Sample Size = 471
Type 1 Error (alpha) = 0.050
Type 2 Error (beta) = 0.001
Statistical Power = 0.999 <<
- Les variables de pondération peuvent être intégrées aux modèles
- Le calcul de puissance implique de bien connaître son sujet (et notamment la taille d’effet envisagée)
- Surestimation de la taille d’effet dans la littérature
Les petits nombres, c’est relatif
Des trop gros nombres ne sont pas toujours avantageux
Pour des designs simples (ANOVA, régressions, etc.) :
**G*Power** - le logiciel : https://www.psychologie.hhu.de/arbeitsgruppen/allgemeine-psychologie-und-arbeitspsychologie/gpower
MorePower - le dépôt github : https://github.com/LewisPeacockLab/MorePower/blob/main/README.md
PANGEA - le dépôt github : https://github.com/jake-westfall/pangea
powerMediation - le package R : https://weiliang.r-universe.dev/powerMediation/doc/manual.html
Power and Precision - le logiciel : https://power-analysis.com/?utm_source=softwareworld.co&utm_medium=referral
pwr - le package R : https://github.com/heliosdrm/pwr & le lien CRAN : https://cran.r-project.org/web/packages/pwr/index.html
pwrss - le package R : https://cran.r-project.org/web/packages/pwrss/vignettes/examples.html#1_Generic
Superpower - le package R : https://cran.r-project.org/web/packages/Superpower/vignettes/intro_to_superpower.html
Pour des SEM (Structural Equation Models) :
semPower - dépôt github : https://github.com/moshagen/semPower & le lien CRAN : https://cran.r-project.org/web/packages/semPower/index.html
simsem - le package R : https://simsem.org/
Pour des modèles mixtes / longitudinaux :
longpower - le package R : https://cran.r-universe.dev/longpower/doc/manual.html
powerlmm - le package R : https://rpsychologist.com/introducing-powerlmm
simr - le package R : https://cran.r-universe.dev/simr/doc/manual.html
webpower - le logiciel en ligne : https://webpower.psychstat.org/wiki/ & le package R : https://cran.r-project.org/web//packages//WebPower/index.html
Pour des analyses de survie :