Table 5 Study quality assessment framework for observational, field studies
Bias area | 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 low | |
Replicates | Multiple samples taken at each site | Single samples taken at each site | |
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 additional file | 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 | |
Research aim consistency | Questions clearly stated and answers match questions | Questions not clearly stated or answers do not match stated questions |