What a pre-survey is. A pre-survey is the baseline measurement taken before an intervention begins. It captures the respondent's starting state on the outcome the program is designed to change. The pre-survey serves as the comparison point for every later measurement; without it, post-survey scores have nothing to be compared against and change attributable to the program cannot be calculated. Pre-survey is sometimes called a baseline survey, pretest, pre-assessment, or pre-intervention measurement.
What a post-survey is. A post-survey is the measurement taken after the intervention ends, using the same questions as the pre-survey wherever possible. The post-survey captures the respondent's state on the outcome at the conclusion of the program. The post-survey is also used informally for any survey administered after an event (post-event survey, post-purchase survey, post-meeting survey), where the goal is feedback rather than delta measurement. The two uses share a name but differ in purpose; this page covers the first use, where Pre and Post are paired for change measurement.
What the delta means. The Pre to Post delta is the score difference on each instrument between the two measurement points, calculated either cohort-wide (average Post minus average Pre) or per-respondent (each respondent's Post minus their own Pre, also called the ipsative delta). Both numbers matter and answer different questions. The cohort delta tells the business sponsor whether the program worked overall. The per-respondent ipsative distribution tells the program manager who moved and who did not, which informs design changes for the next cohort.
Where it sits in research design. A pre and post survey is a quasi-experimental design when there is no control group, or a true experimental design when paired with a randomly assigned control group. Most enterprise and nonprofit programs use the quasi-experimental form because finding a comparable control group is rarely practical. The trade-off is that confounding factors (other things happening in the world during the program window) cannot be ruled out without a control. Benchmark comparison against external reference programs partially addresses this, which is why the analysis section below recommends benchmark anchoring as a routine practice.