Discover the Latest in Biomedical Research Innovation

A two-way ANOVA in SPSS takes one menu and five dialogs, and three of their defaults can quietly mislead you: the Post Hoc button compares the wrong means after an interaction, the right comparisons are uncorrected unless you change a dropdown, and the unequal-variance tests never run in a two-factor model. This SOP runs the analysis correctly, from data entry to a reportable result.

Reviewers examining 100 clinical papers found 65% needed revisions just to explain what their statistical tests were for, and 64% had omitted effect sizes entirely. Statistical reporting problems are rarely about running the wrong analysis; they're about not writing down enough for a reader to judge it. Here's what belongs in the section, built on the SAMPL guidelines: seven things to state in your methods, the results formats that draw fewest queries, and a template you can

Run an ANCOVA and a multiple regression on the same data, specified equivalently, and you get the same F, the same p, and the same coefficients. They are one model with two traditions, and dummy coding is the bridge. So the real question isn't which is correct but which framing makes your result clearest. This piece covers why they're equivalent, what genuinely differs, and how to describe your model so reviewers from either tradition can follow it.

Your treated and control wells started at different confluence, so comparing endpoints with a plain ANOVA measures your treatment effect plus the head start. ANCOVA fixes that by adjusting for a continuous covariate, and usually buys power too. This step-by-step ANCOVA protocol runs 24 numbered steps from covariate choice through reporting, with the assumption checks in the order they need to happen, including the parallel-slopes test most people skip.

SD, SEM, and 95% CI are three different error bars answering three different questions, and they're not interchangeable. The standard error vs standard deviation confusion is where most figures go wrong: SEM is always the smallest, so it makes data look tighter than it is, which is why reviewers flag it most. This piece explains what each bar actually claims, shows one dataset drawn three ways, and tells you which to use, and when to just report SD with your n.

A small p-value tells you a difference is probably real, not that it's big enough to matter. Statistical significance asks whether an effect is distinguishable from noise; biological significance asks whether it's large enough to change a cell, a patient, or a conclusion. Because the p-value shrinks as your sample grows, a big enough study can stamp p < 0.05 on a difference that means nothing. Here's why, with real examples, and what to report instead: effect size and confide