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Adult Weight Management

AWM: Portion Control (2006)


Wansink B, Kim J.  Bad popcorn in big buckets:  portion size can influence intake as much as taste.  J Nutr Educ Behav 2005; 37: 242-245.

PubMed ID: 16053812
Study Design:
Randomized Controlled Trial
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To investigate whether environmental cues such as packaging and container size could influence a food's intake independent of its palatability.
Inclusion Criteria:
Aged 18 - 66 years.
Exclusion Criteria:
Not specifically mentioned.
Description of Study Protocol:


Moviegoers had independently elected to see 1 of 4 showings of the film Stargate, 2 consecutive shows on 2 consecutive evenings.


Randomized Controlled Trial, 2 x 2 between-subjects design.

Blinding used (if applicable)

Not used.

Intervention (if applicable)

Moviegoers randomly assigned to receive free popcorn (fresh or stale, medium or large) and drink.

Statistical Analysis

Random assignment to 4 conditions enabled equivalent comparisons to be made.

Data Collection Summary:

Timing of Measurements

Moviegoers randomly given a medium (120 g) or large (240 g) container of free popcorn that was either fresh or stale (14 days old).  Measurements taken after movie and questionnaire completed.

Dependent Variables

  • Measures of perceived taste on 9-point scale on questionnaire

Independent Variables

  • Buckets of popcorn preweighed prior to distribution with weight marked on bucket bottom.  Following movie, containers collected and reweighed.  Inspections of theatre noted no notable spillage.

Control Variables


Description of Actual Data Sample:

Initial N: 177 moviegoers approached

Attrition (final N):  158 moviegoers, 57.6% male (89.3% agreed to participate).  Fresh popcorn, medium container: n=38, fresh popcorn, large container: n=40, stale popcorn, medium container: n=39, stale popcorn, large container: n=40.

Age:  28.7 years 

Ethnicity: Not mentioned

Other relevant demographics:  Not mentioned 

Anthropometrics:  Moviegoers in each randomized sample were similar in terms of age (28.9, 30.4, 29.0 and 27.2 years of age, F = 0.45, P > 0.20) and in terms of their gender mix (57%, 60%, 62%, 54% male, chi-square = 0.522, P > 0.20). 

Location:  Philadelphia


Summary of Results:


Model n=158 Container Size Freshness of Popcorn Taste Ratings of Popcorn Quality Ratings of Popcorn R2
Full model 0.374 -0.698 0.118 -0.054 0.423

Container and freshness only

0.407 -0.573




Taste and quality only

-- --




Other Findings

Moviegoers who were given fresh popcorn ate 45.3% more popcorn when it was given to them in large containers than medium containers (85.6 vs 58.9 g, F 1, 76 = 38.6, P < 0.01).

This container-size influence is so powerful that even when the popcorn was disliked, people still ate 33.6% more popcorn when eating from a large container than a medium-size container (50.8 vs 38.0 g, F 1,77 = 8.73, P < 0.01).

Container size increased consumption for both the fresh and the stale popcorn (45.3% and 33.6%, respectively), however, the relative increase in consumption was greater for the fresh popcorn than for the stale popcorn (F 1, 154 = 7.42, P < 0.01).

Author Conclusion:
Our findings show that environmental cues, such as container size and portion size, can influence the consumption of even unpalatable foods.  The silver lining of these findings may be that portion size can also be used to increase the consumption of less preferred healthful foods, such as raw vegetables.
Funding Source:
University/Hospital: Scholars Research Fund (University of Pennyslvania's Wharton School); Julian Simon Research and Food and Brand Lab (University of Illinois at Urbana-Champaign)
Reviewer Comments:
Questionnaire not tested for reliability or validity.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? ???
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? ???
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? ???
  4.1. Were follow-up methods described and the same for all groups? ???
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) ???
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? ???
  4.4. Were reasons for withdrawals similar across groups? ???
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? ???
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? ???
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? ???
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? No
  8.2. Were correct statistical tests used and assumptions of test not violated? ???
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes