Because of the possibility of de-anonymising single cases, data are only accessible in not-too-sparse strata, obviating all analyses that use individual case data, for example, regression analyses with simultaneous adjustments for more than one confounder, or even interactions between confounders.
Because data were sparse, the stratum-specific estimates were unstable; consequently, this study was unable to confirm or interpret potential differential effects.
The compression is highly effective at reducing bandwidth consumption due to the high probability of long runs of zeros or ones in the most sparse or most dense strata.
In accordance with previous findings (Bellocchio et al. 1998; Herzog et al. 2006; Cooper et al. 2008), VGlut1 was found to be very abundant in the stratum lucidum and sparse in the pyramidal cell layer, while VGlut2 signals appeared predominantly as immunopositive puncta within the pyramidal layer with a very sparse distribution within stratum lucidum (Fig. 4f).
Significantly, the closely associated neurons of the laminar formation were immunostained with both anti-ephrin-A5 and EphA5 antibodies, while the sparse neurons of the stratum radium were not well stained (Figure 1B; right panel).
Between E14.5 and E18.5, the Tph2 pattern gradually approximates that of Pet1, but does not attain a comparable density (e.g., patchy signal in the periventricular stratum and sparse positive cells superficially; Figs. 8g, o and 9g, o).
In either case the over-dispersion ψ is best estimated from the Pearson chi-squared statistic, though neither this nor other estimates are consistent when data are sparse (few events per stratum) [ 13].
Without matching, when a sample size is small, the analysis can result in many strata with very sparse data.
Matched study can increase the efficiency of the study by balancing strata which overcomes sparse-data problem and it gives the maximum information even sample size is small.
Given the median duration of treatment presented above, there are sparse data for the >24-month strata, especially for the NPH cohort.
