Replies to the four finance and economy questions score 1 for a lot better, 0.5 for a little better and 0 for staying the same. They score -0.5 for a little worse and -1 for a lot worse. The spending climate question scores 1 for right time, 0 for neither and -1 for wrong time. For each of the 5 headline questions, take the mean score, meaning average reply, across respondents. The headline Overall Index Score is the simple mean, meaning equal-weight average, of the 5 question means. It sits on a -100 to 100 scale, published as whole numbers. Quotas for age, sex, region and class keep the sample, meaning those surveyed, representative, with no extra question weights. GfK applies no seasonal adjustment, meaning no smoothing for calendar seasons, unlike European aggregates. The estimated margin of error is +/-2%. Zero is the arithmetic balance point, so negative means net pessimism and positive means net optimism.
This is GfK joint survey work with NIM, a private poll of about 2000 consumers, not official statistics and not the United States Conference Board gauge. The Savings Index stays outside the headline, despite appearing alongside it, and European aggregates can move differently because they use seasonal adjustment.