How Accurately Do Young Adults Recall Childhood Pets? A Validation Study
How Accurately Do Young Adults Recall Childhood Pets? A Validation Study
Christine Cole Johnson
American Journal of Epidemiology ª The Author 2009. Published by the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: . Epidemiologic research shows that pets influence human health, demonstrating both protective and deleterious health risks; therefore, valid definitions of pet exposure would enhance research. The authors determined how well young adults aged 18 years report their early childhood pets. Subjects in an established birth cohort from Detroit, Michigan, born in 1987-1989 (n ¼ 820) were asked a series of questions about pets in the home during their first 6 years of life. Pet recall was compared with annual prospectively collected parental report from 12-18 years prior. Exposure to cats was correctly reported on average 86.3% of the time (95% confidence interval: 85.0, 87.5) and dogs 79.2% (95% confidence interval: 77.7, 80.6) of the time (P < 0.01). Cats and dogs were more likely to be underreported than overreported, from as few as 1.8-fold to as many as 8.3-fold (P < 0.05). Reporting differed by sex of the respondent and current pet ownership. No differences were found in reporting by those who experienced allergy symptoms near dogs or cats. Findings suggest good reliability of young adult pet reporting for ages 0-6 years but that childhood pet exposure may need to be assessed separately depending on the participant's sex and the outcome of interest. animals, domestic; asthma; cats; cohort studies; dogs; hypersensitivity; mental recall; validation studies Correspondence to Charlotte Nicholas, 1 Ford Place, 3E, Detroit, MI 48202 (e-mail: ).
Epidemiologic research suggests that pet exposure may
influence human health starting in utero and continuing into
adulthood (1–9). Several large birth-cohort studies
investigating early-life factors related to allergic disorders have
particularly focused on the role of pets (1–3). Pets have
exhibited both protective and deleterious associations with
human health, and investigations into the effects of pet
exposure on health will likely continue.
Although a number of birth cohort studies have obtained
prospectively collected pet data (1–3), in numerous studies
exposure history is based on participant recall (4–7). In
many such studies, childhood pet ownership (i.e., number
of cats and/or dogs) is based on self-report without
additional measures to verify or ensure accuracy of the report,
potentially leading to bias and conflicting results. There is
little evidence in the literature to quantify the accuracy of
self-report of this important information for epidemiologic
investigations (8). Our goal in these analyses was to
determine the accuracy of self-reported early childhood pet
exposure by participants aged 18 years in a birth cohort study
by comparing their reports with prospective data on
household pets collected from their parents by annual
questionnaires during the participants’ first 6 years of life.
MATERIALS AND METHODS
Subject recruitment and selection
The methodology for the Childhood Allergy Study has
been fully described elsewhere (9). In summary, pregnant
women aged 18 years or older from a geographically defined
area of metropolitan Detroit, Michigan, who belonged to
a health maintenance organization affiliated with the Henry
Ford Health System and had an estimated date of
confinement between April 15, 1987, and August 31, 1989, were
eligible for the study. Study enrollment included providing
written informed consent, completing a predelivery
interview, and having cord blood collected at delivery. Women
were asked to complete annual telephone questionnaires on
the anniversary of their child’s birth until (and including) the
child’s sixth birthday. Answers to questions on
environmental exposures, including household pets, were obtained in
these yearly interviews in addition to information on the
child’s allergic and nonallergic disease outcomes. Upon
conclusion of the Childhood Allergy Study, 835 families
remained eligible for enrollment in follow-up studies.
Recently, we contacted this original Childhood Allergy
Study cohort of 835 children to obtain updated health
information through age 18 years. After their 18th birthday, teens
were contacted to complete 1) a telephone-administered
interview and 2) a clinical evaluation.
Of the 835 teens eligible when the Childhood Allergy
Study ended, 15 withdrew from the study or otherwise
became ineligible prior to the follow-up at age 18 years. Of the
remaining 820 teens, 48 were unable to be evaluated (40
could not be contacted, 3 were enlisted in the military, 3 had
medical conditions precluding them from a personal
interview, and 2 were incarcerated), leaving 772 teens eligible to
participate. Of the 772 teens eligible, 670 (86.8%)
consented to study enrollment. The Henry Ford Health System
Institutional Review Board approved all aspects of the
Childhood Allergy Study.
The telephone questionnaire administered to teens
addressed items on lifetime exposure to animals and to
cigarette and/or other forms of smoke, physical activity, family
history of allergic disease, and residential characteristics in
addition to including demographic questions. Allergic
disease outcomes were also assessed.
Prospective evaluation of pet keeping was reported by
families (usually the mother) at the time of the annual
interviews during the first 6 years of life. Pet keeping was worded
as such: Have you had any pets in your home for more than
2 weeks? If a household pet was present, the type of animal
and number of each type of animal were recorded as well as
whether these animals were kept mostly indoors, outdoors,
or equally indoors and outdoors.
Retrospective report of pet keeping was given by
participants aged 18 years. Specifically, they were asked, Have
you ever lived with any pets or outdoor animals? Follow-up
questions included the types of animals owned and whether
these animals were indoor or outdoor animals. Animals
were categorized as indoors if the teen reported that the
animal stayed indoors for 12 or more hours per day. If the
teen had any pets other than fish, they were asked, Please list
all [indoor/outdoor] pets that you have ever lived with for at
least 1 month. For each pet listed, information was recorded
on the type of pet, age of the participant when living with the
pet, categorization of amount of contact with the animal,
and whether the pet was allowed in the bedroom. In
addition, for all cats or dogs listed, pet breed and weight were
Also obtained from the interview at age 18 years, ‘‘animal
allergy’’ was classified based on the teen’s report of
symptoms. For these analyses, cat or dog allergy at age 18 years
was defined as the teen currently reporting at least one of the
following symptoms when around the pet: coughing,
wheezing, chest tightness, shortness of breath, having a runny or
stuffy nose or starting to sneeze, getting itchy or watery eyes,
or developing hives. ‘‘Ever’’ asthma status was based on the
teen’s report of having received a prior diagnosis of asthma
by a physician. ‘‘Current’’ asthma was defined as ever
having had a physician diagnosis of asthma and at least one of
the following in the 12 months prior to his or her telephone
interview: having asthma symptoms, having an asthma
attack, or taking prescription medications for asthma.
Pet keeping as reported by parents in the prospective
annual interviews was considered as ‘‘truth.’’ The kappa
statistic with 95% confidence intervals was used to measure
agreement beyond chance alone between annual parental
report and teen recall of pet keeping. In this study, if teen
recall agreed with parental report and parental report was
‘‘truth,’’ then kappa is also a chance-corrected accuracy
measure. A kappa coefficient of 1.00 indicates perfect
agreement, whereas a value of 0.00 indicates no agreement
beyond that expected by chance. Guidelines for interpreting
kappa statistics as established by Landis and Koch (10) were
applied, with values of 0.81–1.00 considered ‘‘almost
perfect,’’ 0.61–0.80 ‘‘substantial,’’ 0.41–0.60 ‘‘moderate,’’
0.21–0.40 ‘‘fair,’’ and less than 0.21 ‘‘slight’’ to ‘‘poor.’’
Differences in kappa values within each stratum were tested
with a chi-square statistic (11).
The McNemar test of symmetry was used to determine
whether underreporting was equal to overreporting by teens
whose pet recall did not agree with the prospective parental
report. Cochran-Armitage tests for trend were used to
evaluate trends in animal reporting over time. Because pet
keeping may be differentially reported depending on important
characteristics of the participant, stratification was used to
assess for effect modification. Asthma status (current as well
as ever), clinical atopy to cats and dogs, and self-reported
allergy to cats and dogs were all assessed as potential effect
Teens who participated (n ¼ 670) were on average 18.3
years of age, with 317 (47.3%) male and 645 (96.3%)
Caucasian. Asthma status was known for 664 (99.1%) of
participating teens (for 6 teens, asthma status was
incomplete), with current asthma reported in 59 (8.9%) of teens
and 145 (21.8%) teens ever being diagnosed with asthma.
Two hundred one teens (30.0%) reported allergic symptoms
around cats, and 104 (15.5%) of all teens reported these
symptoms around dogs.
Table 1 presents teens’ report of pets in comparison to
prospectively reported pets by parents when the teen was
a young child. In this analysis, cats and dogs were each
dichotomously categorized as present or not during each of the
first 6 years of life. Because all families did not complete
every annual interview, the denominator varied by year of
life. The presence of cats was correctly reported on average
86.3% of the time (range, 85.0%–87.5%) and dogs 79.2% of
the time (range, 77.7%–80.6%), with this difference being
statistically significant (P < 0.01). Both cats and dogs were
more likely to be underreported than overreported. Degree of
underreporting (percentage underreporting divided by
rroC epR .
8 9 5 7 9 2
o 5 4 6 0 1 9
N 4 4 3 4 4 3
% .27 .42 .53 .45 .66 .83
.o 6 3 4 3 5 2
N 1 1 2 2 3 4
% .02 .65 .43 .52 .39 .46
2 1 1 1 1 1
% .71 .12 .04 .03 .95 .72
7 8 8 8 7 7
% .20 .41 .20 .26 .42 .47
.o 2 8 9 3 2 4
N 1 1 2 2
% .62 .61 .88 .21 .10 .60
1 1 1 1 1
.o 5 4 0 7 3 4
N 7 6 4 5 5 5
% .54 .70 .92 .62 .58 .46
8 8 8 8 8 8
rroC epR .
7 1 6 7 2 0
o 0 8 0 3 5 3
N 5 4 4 4 4 4
Cat (Male Teen)
Cat (Female Teen)
Dog (Male Teen)
Dog (Female Teen)
Year of Life
percentage overreporting) ranged from as little as 1.8-fold
for dogs in the sixth year to as much as 8.3-fold for cats in the
second year (for each age, McNemar’s test for symmetry
P < 0.05). Overreporting of animals was significantly more
frequent with increasing age during childhood
(CochranArmitage test for trend P < 0.01).
Kappa statistics for total cat and dog recall are also
reported in Table 1. Level of agreement, and therefore
accuracy, was similar for both teen recall of the presence
of cat(s) and teen recall of the presence of dog(s) (P > 0.05
for each of the 6 years). As measured by kappa coefficients
and their corresponding 95% confidence intervals, more
accurate recall of cats by those with a history of asthma
was observed during one year (the fifth year of life)
compared with those without a history of asthma (P < 0.05,
data not shown). Differences in reporting of dogs by
asthma status were not statistically significant for any of
the 6 years (all P > 0.05, data not shown). A similar
association was seen for those with current asthma (not
Figure 1 shows pet recall by sex of the teen. Females
tended to more accurately recall their early-childhood dogs
than did their male counterparts, with differences achieving
statistical significance (P < 0.05) for the first, second, and
fourth years of life, but not from ages 5 to 6 years. Females
also tended to more accurately report their cats in the first
4 years of life; however, differences between male and
female reporting of cats did not achieve statistical
significance (all P > 0.05).
Table 2 shows teen recall stratified by current dog and cat
ownership. Teens with one or more dogs in their home at age
18 years were significantly less likely to recall their
childhood dogs for the first, second, fourth, fifth, and sixth years
of life than teens without a dog in the home (P < 0.05).
Teens with one or more cats in the home at age 18 years
were significantly less likely to recall their cats in the fourth
and sixth years of life than were teens without cats (P <
Validating Pet Recall by Young Adults 391
Recall of Dogs
Recall of Cats
No Dog at Age
Dog at Age
No Cat at Age
Cat at Age
0.29, 0.55 <0.05
Abbreviation: CL, confidence limits.
a 0.81–1.00: ‘‘almost perfect’’; 0.61–0.80: ‘‘substantial’’; 0.41–0.60: ‘‘moderate’’ (10).
b For 1 family, data on dogs were missing.
0.05). Teen recall was also stratified by self-reported allergy
symptoms to cats and dogs. Teens with symptoms around
either cats or dogs were as accurate in their reporting of
childhood cats and dogs as those without symptoms (all
P > 0.05, data not shown).
Teen recall was further assessed by original parental
report if the dog(s) or cat(s) was 1) mainly indoors, 2) equally
indoors and outdoors, or 3) mostly outdoors to test whether
pets that spent more time in the home were more often
recalled by teens. Recall of cats did not significantly differ
by categorization of time indoors during any of the 6 years
(all P > 0.05, data not shown); however, recall of dogs did
differ for the fourth and fifth years of life, with, on each
occasion, dogs equally indoors and outdoors the most likely
to be remembered followed by mainly indoor dogs, with
mostly outdoor dogs the least likely to be remembered (both
v2 P < 0.05, data not shown).
For all analyses, cat and dog ownership is reported by
using dichotomized groupings (any cats or dogs vs. none)
but was also assessed as 0, 1, or 2 or more animals (data not
shown). These results did not vary from those for the
dichotomized groupings; therefore, the dichotomized
groupings were chosen for ease of presentation. In addition, for
each analysis, ownership of indoor animals was separately
tested, and these results did not vary from those for total
animal ownership. To minimize misclassification error, data
on indoor and outdoor animals were combined in the
This investigation into teen recall of childhood pet
ownership found that teens correctly reported early (birth–age
6 years) childhood cats and dogs 86.3% and 79.2% of the
time, respectively. In addition, teens were more likely to
underestimate than overestimate the number of pets in their
home. Recall of cats and dogs was on average ‘‘moderate’’
(kappa statistic ¼ 0.41–0.60) (10) and at times achieved
‘‘substantial’’ agreement (0.61–0.80) for female
respondents and those without dogs or cats at age 18 years. Current
dog owners were less likely to recall their childhood dogs 5
of the 6 years assessed as compared with teens without a dog
in the home, while current cat owners were less likely than
teens without a cat in the home to recall their cats from 2 of
the 6 years assessed.
Pet recall did not vary significantly by reported symptoms
around cats or dogs or by year of life, but there was a
positive, significant trend in overreport of cats and dogs by
teens with increasing year of childhood (P < 0.001).
Amount of time the pets spent indoors was largely unrelated
to teen recall of the animal, with the exception of recall of
dogs for 2 of the 6 years assessed. Finally, those with a
history of physician-diagnosed asthma more accurately
reported their cats from the fifth year of life than those
lacking a diagnosis.
One other article on recall of childhood pets was
identified in the literature. Svanes et al. (8) reported
substantial agreement between adults asked about their childhood
pets on 2 separate occasions 9 years apart. However, this
group asked participants about pet keeping as ‘‘a child’’
without defining specific ages when pets were kept and
conducted no prospective evaluation of pets in childhood.
Therefore, we cannot directly compare our findings with
Unlike Svanes et al. (7, 8), we did not use immunoglobulin
E to further classify our participants. Although positive
specific immunoglobulin E is frequently used to dichotomize
people as allergic or not allergic, differential reporting of
childhood pets may be more likely if one recognizes and
reports symptoms rather than relying on specific
immunoglobulin E levels that may not be associated with symptoms
and would largely be unknown to the participant. Those who
have or have ever had asthma symptoms around animals may
be more inclined to remember their childhood pets,
especially if pets triggered their asthma symptoms or if their
family intentionally did not keep pets because of the child’s
Pet characteristics, including numbers of pets in the
home, affect household levels of pet allergen and
biomarkers of bacterial load such as endotoxin (12–14);
therefore, when assessing disease outcomes, these variables
merit evaluation. With an estimated 37.2% of households in
the United States owning a dog and 32.4% owning a cat (an
average of 1.7 dogs and 2.2 cats, respectively, in these
homes) (15), detailed questions regarding cat and dog
ownership during childhood are warranted. Even though our
research focused on allergic disease, recall of childhood pets
may be applicable elsewhere.
Some limitations of our analysis are that pet reporting at
the time of pet ownership was completed by the parent of
the teen and not the teen himself or herself; however,
prospective data collection on infants requires report by others.
We focused on accuracy of teen report of his or her
household pet exposure during the first 6 years of life—a time
when he or she is likely to have limited recall.
It is possible that pets residing in the home for longer
periods of time during childhood were more accurately
remembered by teens than were pets in the home for shorter
periods of time, or that pets allowed in the child’s bedroom
or those having more daily interaction with the child would
be more likely to be remembered by teens. Unfortunately,
we are unable to address these issues because these data
were not collected during childhood.
Furthermore, racial/ethnic diversity of this cohort is
limited and varies from the national averages, so this factor may
limit application of our findings to the general population.
However, the study population was homogenous with
respect to race/ethnicity and provided a good sample size
for our analyses.
Our findings suggest good accuracy during young
adulthood of pet reporting for ages 0–6 years but that childhood
pet recall may vary depending on the sex of the participant
and the health outcome of interest. This variance may
impact the results of epidemiologic studies that rely on
retrospective evaluation of childhood pet exposure.
Author affiliations: Department of Biostatistics and
Research Epidemiology, Henry Ford Health System, Detroit,
Michigan (Charlotte Nicholas, Ganesa Wegienka, Suzanne
Havstad, Christine Cole Johnson); Division of Allergy and
Clinical Immunology, Department of Internal Medicine,
Henry Ford Health System, Detroit, Michigan (Edward
Zoratti); and Medical College of Georgia, Augusta, Georgia
Funding was provided by the National Institute of Allergy
and Infectious Diseases.
The authors thank the Childhood Allergy Study families
for their continued participation in this study as well as the
Childhood Allergy Study interviewers and clinic and
laboratory staff for their dedication to this project.
Conflict of interest: none declared.
1. Aichbhaumik N , Zoratti EM , Strickler R , et al. Prenatal exposure to household pets influences fetal immunoglobulin E production . Clin Exp Allergy . 2008 ; 38 ( 11 ): 1787 - 1794 .
2. Remes ST , Castro-Rodriguez JA , Holberg CJ , et al. Dog exposure in infancy decreases the subsequent risk of frequent wheeze but not of atopy . J Allergy Clin Immunol . 2001 ; 108 ( 4 ): 509 - 515 .
3. Perzanowski MS , Chew GL , Divjan A , et al. Cat ownership is a risk factor for the development of anti-cat IgE but not current wheeze at age 5 years in an inner-city cohort . J Allergy Clin Immunol . 2008 ; 121 ( 4 ): 1047 - 1052 .
4. Radon K , Windstetter D , Poluda AL , et al. Contact with farm animals in early life and juvenile inflammatory bowel disease: a case-control study . Pediatrics . 2007 ; 120 ( 2 ): 354 - 361 .
5. Swensen AR , Ross JA , Shu XO , et al. Pet ownership and childhood acute leukemia (USA and Canada ). Cancer Causes Control . 2001 ; 12 ( 4 ): 301 - 303 .
6. de Meer G , Toelle BG , Ng K , et al. Presence and timing of cat ownership by age 18 and the effect on atopy and asthma at age 28 . J Allergy Clin Immunol . 2004 ; 113 ( 3 ): 433 - 438 .
7. Svanes C , Heinrich J , Jarvis D , et al. Pet-keeping in childhood and adult asthma and hay fever: European Community Respiratory Health Survey . J Allergy Clin Immunol . 2003 ; 112 ( 2 ): 289 - 300 .
8. Svanes C , Dharmage S , Sunyer J , et al. Long-term reliability in reporting of childhood pets by adults interviewed twice, 9 years apart . Results from the European Community Respiratory Health Survey I and II. Indoor Air . 2008 ; 18 ( 2 ): 84 - 92 .
9. Ownby DR , Johnson CC , Peterson EL . Maternal smoking does not influence cord serum IgE or IgD concentrations . J Allergy Clin Immunol . 1991 ; 88 ( 4 ): 555 - 560 .
10. Landis JR , Koch GG . The measurement of observer agreement for categorical data . Biometrics . 1977 ; 33 ( 1 ): 159 - 174 .
11. Fleiss JL , Levin B , Paik MC . Statistical Methods for Rates and Proportions . 3rd ed. Hoboken, NJ: Wiley-Interscience; 2003 .
12. Nicholas C , Wegienka G , Havstad S , et al. Influence of cat characteristics on Fel d 1 levels in the home . Ann Allergy Asthma Immunol . 2008 ; 101 ( 1 ): 47 - 50 .
13. Arbes SJ Jr, Cohn RD , Yin M , et al. Dog allergen (Can f 1) and cat allergen (Fel d 1) in US homes: results from the National Survey of Lead and Allergens in Housing . J Allergy Clin Immunol . 2004 ; 114 ( 1 ): 111 - 117 .
14. Bufford JD , Reardon CL , Li Z , et al. Effects of dog ownership in early childhood on immune development and atopic diseases . Clin Exp Allergy . 2008 ; 38 ( 10 ): 1635 - 1643 .
15. American Veterinary Medical Association. U.S. Pet Ownership & Demographics Sourcebook ; 2007 . (http://www. avma.org/reference/marketstats/ownership.asp). ( Accessed October 3 , 2008 ).