For each of the following statements about balance and overlap in observational studies, choose whether the statement is true of false. a.) In an observational study, imbalance on a given covariate implies a lack of overlap for that covariate. TRUE FALSE b.) If treatment and control groups have the same average value for a given covariate, then the groups will usually have high overlap for that covariate. TRUE FALSE c.) In an observational study, complete overlap for a single covariate does not imply complete overlap for unobserved covariates. TRUE FALSE d.) When there is only partial overlap on key covariates within a given dataset, extrapolation will be required in order to produce any valid causal estimates. TRUE FALSE