Domain of bias | Characteristic | Low risk of bias | High risk of bias |
---|---|---|---|
Study design and sampling | Pairing of nutrient and chl-a measurements | Nutrient and chl-a measurements taken at same place and time or index period | Nutrient and chl-a measurements are not paired in time and space |
Study timeframe | Sampling includes relevant periods over multiple years | Sampling occurs only over a single season or year | |
Gradient definition | Gradient based on a nutrient related variable or its causal antecedent | Gradient based on a common causal descendant of TP, TN or chl-a | |
Sample size | Acceptable # sites (≥ 10) across gradient | Low # sites (< 10) across gradient | |
Event-based replicates (sample replicates) | Multiple samples taken during each sampling event for nutrient and chl-a | Single samples taken during each sampling event for nutrient and chl-a | |
Site-based temporal replicates (within-site replicates) | Multiple samples taken at each site (over study period) | Single samples taken at each site (over study period) | |
Randomization of sampling (selection bias) | Some form of randomized site selection (e.g., stratified random sampling) | No randomization of site selection | |
Confounding factors | If not controlled by study design, confounding factors are measured and adjusted for in statistical analysis | Confounding factors reported and not accounted for, or are likely, and are not able to be adjusted for post hoc | |
Data analysis and results | Clarity and detail | Analysis methods described in detail sufficient to permit repeating | Missing information not allowing for repeatability |
Uncertainty | Some estimate of uncertainty in effect or relationships provided (e.g., confidence intervals, standard error, standard deviation, etc.) | No estimates of uncertainty provided | |
Reporting bias | All variables, measurements, and statistical tests mentioned in methods are reported in results or supplementary material | Some variables, measurements, or statistical tests mentioned in methods are not reported | |
Other biases | Detection bias | No indication that outcomes were measured differently in high versus low exposure sites | Some indication that outcomes were measured differently in high versus low exposure sites |
Attrition bias | No differences in loss of high versus low exposure sites | Differences in loss of high versus low exposure sites |