For small sample sizes, split training/test evaluation produces downward bias and instability in estimated prediction accuracy, and cross-validation or 0.632 bootstrap resampling is preferable (Molinaro et al., 2005).
Moreover, values of the propensity score near zero or one can lead to instability in the estimates as well as poor finite sample performance of the IPW estimator (Busso et al. 2013).
This is known as weak identification and may lead to instability in parameter estimates, bias, and poor coverage properties of asymptotically derived confidence intervals.
As well as lack of identification, weak instruments can lead to bias, instability in parameter estimates, and underestimated standard errors (28).
Extending the model to include protein trees of sizes 16 to 100 yields a similar slope (0.080), with a reduced linear fit coefficient of 0.656 due to instability in mean estimates for larger protein tree sizes.
Following equation (2), the model was first estimated with the linear, squared and cubic coverage terms: ln C = a 0 + a 1 w + b 1 q + b 2 q 2 + b 3 q 3 + c 1 x 1 + c 2 x 2 + c 3 x 3 + c 4 x 4, The regressions with higher order terms in coverage were potentially collinear causing instability in the estimates.
a Indicates instability in the estimate due to small numbers.
The EBS technique can be used to adjust for instability in the risk estimates caused by heterogeneity in the distribution of cases and the population.
There was a small amount of correlation (r = 0.55) between adjacent days, causing some instability in the PM2.5 estimates in an unconstrained distributed lag model.
Second, only about 1,000 women were diagnosed with IHD or pulmonary mortality, which may introduce some instability in the risk estimates.
