BY-COVID - WP5 - Baseline Use Case: COVID-19 vaccine effectiveness assessment

Matching cases to controls (1:1) and assessing covariate balance after matching

A sequence of nested (daily) trials are emulated with increasing time (t1, t2, …, tn), iterating over the days in the enrollment period. At each eligible time during the enrollment period, the vaccination status of eligible individuals is assessed and every individual who has completed a primary vaccination schedule at that time (coded here as initiation of the intervention strategy when emulating a nested target trial) is matched to an individual who has not (yet) completed the primary vaccination schedule (coded here as the control strategy when emulating a nested target trial). Newly vaccinated individuals (completing a primary vaccination schedule) are eligible for inclusion in the study, even if they had previously been selected in the “no (or partial) vaccine group”. Vaccinations have been administered in the context of national public health programs, without interference/manipulation of the research subjects.

We assess the covariate balance, which is the extent to which the distribution of covariates is similar across the intervention groups.

Standardized Mean Differences

The Standardized Mean Difference (SMD) represents a standardized difference in mean between contrasted intervention groups for each covariate.

Means intervention group Means control group Standardized mean difference
distance 0.898852559 0.894964209 0.2053042329
sex_cd0 0.017416364 0.009977827 0.0568622458
sex_cd1 0.473374264 0.506651885 -0.0666498088
sex_cd2 0.509209372 0.483370288 0.0516869362
age_cd10 0.117027941 0.119733925 -0.0084179597
age_cd11 0.129933592 0.124168514 0.0171462146
age_cd12 0.127928831 0.143015521 -0.0451683046
age_cd13 0.111514848 0.096452328 0.0478526717
age_cd14 0.096604436 0.087583149 0.0305373248
age_cd15 0.068287182 0.073170732 -0.0193608748
age_cd16 0.044480642 0.046563193 -0.0101016068
age_cd17 0.026061897 0.017738359 0.0522443422
age_cd18 0.023180053 0.023281596 -0.0006748217
age_cd2 0.001754166 0.001108647 0.0154260491
age_cd3 0.002380654 0.000000000 0.0488501289
age_cd4 0.007267260 0.005543237 0.0202974469
age_cd5 0.013156246 0.011086475 0.0181648672
age_cd6 0.027064278 0.021064302 0.0369750888
age_cd7 0.044480642 0.042128603 0.0114087784
age_cd8 0.063400576 0.078713969 -0.0628416921
age_cd9 0.095476757 0.108647450 -0.0448177371
residence_area_cd731 0.155870192 0.146341463 0.0262693175
residence_area_cd732 0.149855908 0.154101996 -0.0118961317
residence_area_cd733 0.694273901 0.699556541 -0.0114661965
pregnancy_blTRUE 0.025435409 0.036585366 -0.0708187905
institutionalized_blTRUE 0.036461596 0.027716186 0.0466581831
foreign_blTRUE 0.148227039 0.137472284 0.0302673847
socecon_lvl_cd1 0.022678862 0.018847007 0.0257383002
socecon_lvl_cd2 0.137702042 0.118625277 0.0553612471
socecon_lvl_cd3 0.360481143 0.375831486 -0.0319705515
socecon_lvl_cd4 0.344067160 0.338137472 0.0124818939
socecon_lvl_cd5 0.135070793 0.148558758 -0.0394616672
comorbidities_blTRUE 0.501190327 0.483370288 0.0356401786
immunestatus_blTRUE 0.275654680 0.276053215 -0.0008918898
Means intervention group Means control group Standardized mean difference
distance 0.504167134 0.4958328661 0.1653647312
sex_cd0 0.017532551 0.0091530231 0.0638466216
sex_cd1 0.472218641 0.4972283099 -0.0500967268
sex_cd2 0.510248808 0.4936186670 0.0332672704
age_cd10 0.116668815 0.1299471445 -0.0413622598
age_cd11 0.130978471 0.1396158309 -0.0256015220
age_cd12 0.127884491 0.1358772721 -0.0239332652
age_cd13 0.111512183 0.1128013407 -0.0040956168
age_cd14 0.095784453 0.0955266211 0.0008760980
age_cd15 0.068067552 0.0666494779 0.0056303658
age_cd16 0.044862705 0.0408663143 0.0193059988
age_cd17 0.025654248 0.0201108676 0.0350621444
age_cd18 0.023075931 0.0190795411 0.0266169248
age_cd2 0.001804821 0.0006445791 0.0273353011
age_cd3 0.002449401 0.0012891582 0.0234720675
age_cd4 0.007219286 0.0041253062 0.0365463212
age_cd5 0.013149413 0.0091530231 0.0350823769
age_cd6 0.027201238 0.0219156891 0.0324925824
age_cd7 0.044347041 0.0411241459 0.0156553863
age_cd8 0.063684414 0.0638133299 -0.0005279326
age_cd9 0.095655537 0.0974603584 -0.0061363800
residence_area_cd731 0.156117056 0.1482531907 0.0216655522
residence_area_cd732 0.150058012 0.1459327059 0.0115513289
residence_area_cd733 0.693824932 0.7058141034 -0.0260123324
pregnancy_blTRUE 0.025009669 0.0201108676 0.0313715287
institutionalized_blTRUE 0.037127756 0.0297795540 0.0388639897
foreign_blTRUE 0.148768854 0.1410339049 0.0217359035
socecon_lvl_cd1 0.022560268 0.0108289287 0.0790006160
socecon_lvl_cd2 0.137811009 0.1348459456 0.0086018299
socecon_lvl_cd3 0.359804048 0.3746293670 -0.0308897622
socecon_lvl_cd4 0.345752224 0.3555498260 -0.0205999508
socecon_lvl_cd5 0.134072451 0.1241459327 0.0291330787
comorbidities_blTRUE 0.501095784 0.5005801212 0.0010313290
immunestatus_blTRUE 0.277684672 0.2763955137 0.0028785040

Propensity score distribution