Barriers to and Facilitators of Iron Therapy in Children with Iron Deficiency Anemia

Abstract

Objective:

To characterize barriers to and facilitators of successful iron therapy in young children with IDA from an in-depth parental perspective.

Study design:

Prospective, mixed-methods study of children age 9 months to 4 years with a diagnosis of nutritional IDA by clinical history and laboratory criteria and their parents. Clinical data were obtained from the electronic health record. Semi-structured interviews focused on knowledge of IDA, clinical effects, experience with iron therapies, and motivation were conducted with the parent who identified as the child’s primary caregiver.

Results:

Twenty patient-parent dyads completed the study; 80% (n=16) identified as Hispanic/Latino (white). Patients’ median age was 23 months (50% male); median initial hemoglobin concentration was 8.2 g/dL and duration of oral iron therapy was 3 months. Parents’ median age was 29 years (85% female); 8 interviews (40%) were conducted in Spanish. Barriers included difficulty in administering oral iron due to side effects and poor taste. Facilitators included provision of specific instructions, support from health care providers and additional caregivers at home, motivation to benefit child’s health, which was strengthened by strong emotional reactions (ie, stress, anxiety) to therapy and follow-up, and an appreciation of child’s improvement with successful therapy completion.

Conclusions:

Our findings support the need for interventions designed to promote oral iron adherence in children with IDA. Rather than focusing on knowledge content related to IDA, interventions should aim to increase parental motivation by emphasizing health benefits of adhering to iron therapy and avoidance of more invasive interventions.

Iron deficiency due to excessive cow milk intake and low-iron diet affects approximately 15% of children age 1 to 2 years of age; approximately 3% have frank iron deficiency anemia (IDA).(1) Children of Hispanic/Latino ethnicity, from low-income and/or primarily Spanish-speaking homes are disproportionately affected.(2–4) Critically, IDA often occurs at a period of rapid neurodevelopment(5, 6) and is associated with inferior neurocognitive outcomes, poorer executive functioning, and decreased visual and auditory processing time.(7–9) Oral iron therapy mitigates the consequences of IDA,(10) and most patients who successfully adhere to therapy have a full recovery within a typical 3 to 6 month treatment course. However, rates of non-adherence are high due to its unpleasant effects and bad taste.(11) Given that more severe and chronic IDA is associated with worse outcomes, such high rates of incomplete therapy may prolong the extent and severity of its negative consequences.

In-depth studies examining barriers to oral iron therapy adherence in young children are lacking. Even fewer studies exist to assess facilitators of its adherence. Qualitative research is a vehicle that can ascertain important information from relevant stakeholders.(12) Information derived from the parental perspective can be utilized to develop interventions that more effectively address elements of care that are important for patients and thereby increase treatment success.(13) The objective of this study was to characterize barriers to and facilitators of iron therapy in young children with nutritional IDA from their parents’ (i.e. primary caregiver’s) perspective.

METHODS

This was a prospective, mixed-methods study conducted in the outpatient hematology clinic of the Texas Children’s Cancer and Hematology Center at Texas Children’s Hospital in Houston, Texas, a large, freestanding tertiary care children’s hospital. Quantitative clinical data were abstracted from the electronic health record on children with nutritional IDA and qualitative data obtained via semi-structured interviews with parents who identified as their child’s primary caregiver at home.(14) Individual in-depth interviews were conducted, and themes representing the parental experience were identified.(12) All study procedures were approved by the Institutional Review Board of Baylor College of Medicine (Protocol H-40112).

Participants and Recruitment

Potential patients were identified by screening the outpatient hematology clinic schedule. Children age 9 months to 4 years with nutritional IDA, defined as a history of excessive cow milk intake (>24 ounces per day) or exclusive breast milk without iron supplementation, and laboratory indices: hemoglobin concentration (Hgb) ≤10 g/dL, mean corpuscular volume (MCV) ≤70 fl, serum ferritin ≤15 ng/mL or total iron binding capacity ≥425 mg/dL,(10, 15) were identified for recruitment. Children with other causes of anemia, IDA due to an underlying gastrointestinal disorder, chronic inflammatory conditions, history of prematurity (less than 30 weeks gestational age), or who were unable to tolerate oral medications were excluded. Patient-parent pairs were eligible for enrollment if the parent who identified as the child’s primary caregiver spoke English or Spanish. Purposive sampling was utilized to recruit parents from both language preference groups to ensure adequate representation of each group. Patients could have received iron therapy for up to 12 months duration at the time of enrollment. Parents were approached for enrollment during their child’s regularly scheduled clinic visit, and written informed consent was obtained prior to study participation.

Data Collection

After explaining the study objective (i.e., to better understand the parent’s perspective on iron therapy), a research coordinator trained in qualitative methods interviewed each parent in-person in association with a scheduled clinic visit in a private examination room. Interviews with primarily Spanish-speaking parents were conducted with an in-person professional Spanish interpreter. All interviews were audio-recorded.

Interview Guide

Each interview followed a semi-structured interview guide with open-ended questions; probes were used to clarify, understand, and/or expand responses as appropriate. The guide was developed with a multidisciplinary team consisting of three pediatric hematology-oncology subspecialists, one academic general pediatrician with expertise in health disparities, and a behavioral science researcher with expertise in nutrition and qualitative research methods, and informed by the self-determination theory of motivation (SDT).(16) The SDT proposes that behavior is motivated by three basic psychological needs: autonomy (i.e. the belief that the individual has a choice and control), competence (i.e. the belief that one has the knowledge, skill, and ability to successfully perform a particular behavior), and relatedness (i.e. sense of connection with self and important others, such as a family member, in regards to a particular behavior). Satisfaction of these needs enhances intrinsic (i.e., self-directed) motivation to perform the behavior. The SDT was selected as the theoretical framework for this study based on the hypothesis that motivation would be an important component of the parents’ likelihood of adhering to their child’s prescribed oral iron therapy.(16) Interview questions are shown in Table I. At the end of each interview, parents completed a demographic survey.

Table I.

Interview Questions for Parents of Children with IDA

Diagnosis of IDA

1. Let’s begin by talking about the definition of iron deficiency anemia. How would you describe iron deficiency anemia to a friend or family member?

Consequences of IDA

2. How does iron deficiency anemia affect your child’s health (either in a good or bad way)? If the anemia was not found, what do you think would have happened?

Oral iron medicine / Treatment regimen

3. Tell me about the iron treatment that your child received. In your opinion, why was your child given an iron medicine?

Adherence to oral iron / Motivation

4. What was it like to give the iron medicine to your child? What, if anything, made it hard to give the medicine to your child? What, if anything, made it easier to give the medicine to your child?

5. What were your reasons for giving your child the iron medicine?

6. What are the biggest problems in giving iron medicine for several months?

7. What would help parents take care of a child with iron deficiency anemia?

8. In your opinion, what could be done to motivate parents to complete iron deficiency anemia treatment?

Alternate treatment options

9. Did your provider discuss with you other ways to treat iron deficiency anemia? If so, what were they?

10. [Brief overview of intravenous iron therapy provided.] Tell me your thoughts about this type of treatment option [intravenous iron therapy].

Summarizing question

11. What is the best way for you to receive information about iron deficiency anemia and its treatment options?

Interviews were professionally transcribed verbatim in the original language spoken; all identifiers were removed to protect confidentiality. Spanish language transcripts were then professionally translated into English. Analysis was conducted on the English language transcripts and were reviewed for accuracy by the PI, who read each transcript while listening to the corresponding audio recording and made corrections, if indicated. After 20 interviews, the research team determined that theoretical saturation was achieved, as evidenced by the lack of emergence of new information, and enrollment was closed. All interviews were conducted from February 2017 through January 2018.

Data collection from the electronic medical record included primary provider referral information, dietary history, oral iron therapy (including dosing and duration), receipt of intravenous iron and/or red blood cell transfusion, hematologic, and iron laboratory measures, as well as duration of hematology follow-up.

Statistical Analyses

A hybrid thematic analysis approach was used.(17) Utilizing a preliminary codebook designed with a priori codes, 2 trained members of the research team reviewed transcripts multiple times to develop familiarity with responses.(12, 16) A priori codes were then applied. Emergent codes (i.e. concepts that were identified or evolved from data review) were generated to help ensure the participants’ voices were captured. After analysis, members reviewed codes together, and through discussion, codes were grouped into basic themes followed by higher order themes to create a thematic network (Figure). Themes that emerged from parent interviews were utilized to better understand IDA and iron therapies from the parental perspective.

FIGURE.

Thematic Network of Parents’ Perceptions of IDA and Iron Therapy

RESULTS

Twenty patient-parent dyads completed the study (Table II). Patients’ median age was 23 months (range 12 to 40); 50% (n=10) were male. Parents’ median age was 29 years (range 29 to 41); the majority (85%, n=17) were female; 80% (n=16) of families identified as Hispanic/Latino (White). Eight interviews (40%) were conducted in Spanish. Patients’ median initial Hgb was 8.2 g/dL (range 4 to 9.5). Patients’ median final available Hgb was 11.3 g/dL (range 7.2 to 13.1). During their hematology treatment course, the majority of patients (n=13, 65%) were treated with ferrous sulfate and a smaller portion (n=6, 30%) received iron polysaccharide complex (Table II). The most common oral iron treatment regimen included elemental iron dosing of 3 mg/kg/day (range 1 to 6 mg/kg/day) administered once daily (70%). Median duration of oral iron therapy of enrolled subjects was 3 months. Two patients (10%) had received intravenous iron therapy; another 2 (10%) had received red blood cell transfusion for severe anemia.

Table II.

Demographic and Clinical Characteristics of IDA Patients and Their Parents

Patient-Parent Dyads, N=20
Race/ethnicity (self-identified), n (%)
White, Hispanic/Latino	16	(80%)
Asian	3	(15%)
Black or African American	1	(5%)
Patients, N=20
Age at interview, median (range), months	23	(12 to 40)
Female Sex, n (%)	10	(50%)
Initial hemoglobin concentration, median (range), g/dL	8.2	(4 to 9.5)
Final hemoglobin concentration, median (range), g/dL	11.3	(7.2 to 13.1)
Therapy
Receipt of packed red blood cell transfusion, n (%)	2	(10%)
Oral iron therapy, n (%)
Ferrous sulfate	13	(65%)
Iron polysaccharide complex	6	(30%)
Poly-vi-sol with iron	1	(5%)
Oral iron therapy duration, median (range), months	3	(1 to 12)
Received intravenous iron therapy (second-line), n (%)	2	(10%)
Parents, N=20
Age at interview, median (range), years	29	(20 to 41)
Female Sex, n (%)	17	(85%)
Primarily Spanish-speaking, n (%)	8	(40%)
Educational attainment (n=19), n (%)
Less than high school	6	(32%)
High school / Graduate Equivalent Degree (GED)	5	(26%)
Some college	6	(32%)
Bachelor degree	2	(11%)
Annual household income, median bracket	35 to 50K
Total children in home, median (range)	2	(1 to 5)
Number of caregivers in home, median (range)	2	(1 to 4)

Themes

Under the global theme of parents’ perceptions of IDA and iron therapy, 3 organizing themes emerged: knowledge of IDA, experience with iron therapy, and motivation to adhere to therapy (Figure). Each organizing theme had 2 to 6 basic themes, discussed separately below. Given that the majority of enrolled subjects identified as Hispanic/Latino ethnicity, an extensive analysis based on ethnicity was not performed.

Review of interview transcripts with the four non-Hispanic/Latino parent participants found no significant differences in themes from that subset compared with the participants as a whole. No significant differences were identified between the English-speaking and Spanish-speaking participants. Quotes supporting themes are presented in Table III; for clarity, several key quotes are embedded in the text.

Table III.

Themes and Quotes from Parents of Children with IDA

Themes	Quotes
IDA Knowledge
Lack of nutrients / Low red blood cells	“Since they released her from the hospital, I should have been giving her iron, but I didn’t… ‘cause I didn’t know it was gonna turn to anemia.”
	“Feed them food that has iron in it. Do not let them take in so much milk.”
	“…the iron level is low in the blood…because he’s not getting the adequate nutrients as he should…”
Oxygen / Effects on heart	“…when you breathe in oxygen, the oxygen is transported through your blood to your heart and that’s why he could have heart problems, I assume. So that’s why it’s fairly serious.”
Anemia symptoms	“Yea, well he really didn’t experience much other than the paleness and not having enough color. He looked really yellow. But energy, now that I see it, his energy was kind of low.”
	“I did not know about her blood level, she was not just concentrating or anything, she was looking pale…she was not eating. She was picking up dirt. She was only surviving on milk and no other thing.”
	“She looked more tired, she wanted to sleep more. She played for a while, and then she wanted to rest…”
Experience of iron therapy
Blood transfusion	“…our doctor was concerned that she is [has a] very low level of blood, then she might, you know, get a blood transfusion…but I was scared about it. I was very concerned because she is so small…and it is not easy. I am glad that we did not need that.”
	“…it has to be pretty intense for me to really feel comfortable for her to get a blood transfusion, she…already [has] anxiety with needles as it is.”
Oral iron - barriers	“It was hard for me because she didn’t want to take it [because of] the taste of the iron and the smell.”
	“…there was no way he wanted to drink it. He spit it out, and it was a battle to try to get him to [take] it.
	“Every time we’d give it to her, she’d throw it up.”
Oral iron – facilitators	“…her [doctor] informed me on things to do. Don’t give it between meals, follow it with orange juice, and don’t give her milk after it…So, I felt like that was very helpful.”
	“I hold him like a baby, and I just shoot it [the iron drops] in there. So, I haven’t had any trouble so far. I mean, he doesn’t like it. As soon as he sees it he tries to run away, but then I just grab him, and he takes it pretty good.”
	“At first it was hard ‘cause she didn’t like it…it still takes two people to give it to her.”
	“My husband would hold his hands, I put his hands back and just give it to him on the side of his cheek, and he takes it…”
	“We do have an alarm on our phone that at six…we already know, the timer goes off, it is time to give him…his iron, so that is how we have been giving and keeping track…it is difficult, but it is manageable.”
Intravenous iron - preference for oral iron	“…it would have to be a severe case for me wanting to really try something like that, I would rather go for the more natural route at the moment.”
Intravenous iron - fear	“…they tell us about the intravenous one if this doesn’t work, but definitely try to make this [oral iron] work so we won’t have to go that route…I’m sure it would be hard on him, so we’re definitely trying this out first…I mean kids and needles…”
	“I’m kind of sad about [him getting intravenous iron]. As long as he don’t react to it, if it’s gonna help him, I’m all for it.”
Intravenous iron - second-line therapy	“No, first oral [iron] depending on the response, and then in case the kid is not responding and is getting traumatized by the medications, I would say to her tell your pediatrician to give it through the vein…”
	“Probably if she was not getting better [with oral iron] then I wouldn’t have a problem trying…I go with whatever the doctor recommends” .
Intravenous iron - preference over oral iron	“He was like, traumatized [by iron drops]. He didn’t want to eat, he had diarrhea, not constipation, diarrhea. That’s why we decided to give it to him through the vein.”
	“I thought it [intravenous iron] was better [than oral iron] …it is a lot better for me. It hurts her a little bit, but it is a lot better for me because she got it really quick, and I start seeing results very fast.”
Motivation for therapy
Emotional stress / Avoidance of trauma	“And then right when we came here [to the hospital] they saw the chart, and they took her in…the doctors came in, it was pretty scary.”
	“We were feeling stress. I’ve been stressing about…I mean, he’s not the best eater. He looks healthy [but] he’d rather drink his bottle…”
	“He [patient’s father] hates seeing him get poked and take blood out and things like that…he hates all of this.”
	“Just explain to parents…it could go real bad if you don’t supplement your baby with iron. It could be dangerous because their anemia could get worse, and we don’t wanna be going through all this.”
Positive effects on child’s health	“I wanted him to get well. I wanted him to have it. I was pushing for him to have the medication. I know that it’ll help him.”
	“We would share with the other family that it’s worth it to do the treatment…because we see changes in her, like her skin color used to be a little yellow but now her skin color is normal. We would say very good changes; previously she used to take a lot of naps and sleep a lot, but now she’s very active and plays a lot more.”
	“He has been doing good [sic]. I mean, it is hard to give it [the oral iron] to him…you know, taste, we have to fight him, but [he] has been taking it, and ever since he has been taking it we noticed that, he has not been eating as much dirt…”
	“I was happy with it [oral iron] because I gave the iron medication in liquid and gave foods with iron, and within two months she recovered.”

Knowledge of IDA

Parents expressed a basic understanding of the cause of IDA, described as a lack of nutrients, and its clinical consequences of low red blood cells and symptoms of anemia (Table III).

Lack of nutrients

Many parents regretted not being better informed about preventive dietary measures. Specifically, they did not realize how critical iron was to their child’s health and the impact of dietary choices on overall iron intake. Several parents admitted that although their children were “picky eaters,” they thought that cow’s milk provided adequate nutrition and did not realize that excessive intake could result in anemia.

Low red blood cells, Oxygen / Effects on heart, Anemia symptoms

Parents were consistently able to define IDA but gave variable responses to its clinical effects on their child, ranging from oxygen delivery and cardiac effects to skin pallor and energy. Some misinformation was also present, including concern that untreated anemia could progress to leukemia. Although deeper understanding was often absent, most understood that IDA affects multiple parts of the body, and in retrospect, 13 parents (65%) were able to recall anemia symptoms their children had been displaying prior to initiation of iron therapy such as poor concentration, pallor, and increased sleepiness. “Yea, well he really didn’t experience much other than the paleness and not having enough color. He looked really yellow. But energy, now that I see it, his energy was kind of low” (Parent 4).

Experience with iron therapy

Several important aspects of therapy, including impact of blood transfusion, and perception of and experienced benefits from either oral or intravenous iron therapy, were mentioned (Table III).

Blood transfusion

Parents reported anxiety with regard to their child’s actual or potential need for a blood transfusion, due to the child’s young age.

Oral iron – Barriers

Parents had contrasting views on oral iron. Negative features including poor taste and resultant difficulty in administering it to their child, were identified as barriers. In retrospect, some parents noted that giving either intravenous iron or a transfusion would have allowed them to avoid constant “battles” with their child over oral iron therapy.

Oral iron - Facilitators

Specific administration instructions, direct encouragement from health care providers (i.e. physicians, nurses), and caregiver support in the home, were all facilitators of oral iron therapy. One parent (5) stated that her child’s doctor “…informed me on things to do. Don’t give it between meals, follow it with orange juice, and don’t give her milk after it…So, I felt like that was very helpful.” Setting an alarm, having patience with the duration of therapy required, and transition to better tasting formulations were also mentioned as facilitators in a subset of parents.

Intravenous iron – Preference for oral iron, Fears

Several parents expressed preference for oral iron therapy when provided a description of the alternative of intravenous iron. Others explicitly expressed fear of their child receiving more “intensive” intravenous iron therapy as well as sadness of their having “failed” oral iron therapy.

Intravenous iron – Second-line therapy, Preference over oral iron

Despite its associated fears, most parents demonstrated willingness for intravenous iron, if necessary. Regarding when to transition from oral to intravenous iron, decision-making was deferred to their medical provider. Two parents whose children received both oral and intravenous iron both reported that they wished their child had been treated more aggressively upfront to minimize the time it took for him to get well.

Motivation for therapy

Parental motivation fell into two broad categories: emotional stress for both parent and child, and the child’s physical health (Table III).

Emotional stress / Avoidance of trauma

Parents frequently expressed the desire to minimize their child’s negative or “traumatic” experiences related to both therapy and ongoing follow-up care. One mother reported that her partner (e.g. patient’s father) stopped attending medical visits because he was so upset at seeing his child have blood drawn. When asked what they would tell to other parents of children with IDA, parents provided encouragement while also acknowledging the difficulties associated with care. “Just explain to parents…it could go real bad if you don’t supplement your baby with iron. It could be dangerous because their anemia could get worse, and we don’t wanna be going through all this” (Parent 3).

Positive effects of iron therapy on child’s health

Several parents explicitly stated they were motivated to get their child’s iron levels up because they knew it would help him/her. “I wanted him to get well. I wanted him to have it. I was pushing for him to have the medication. I know that it’ll help him” (Parent 11). Fourteen parents (70%) noted positive effects in their child’s health including improved skin color, increased energy, and less pica. Prevention of more severe disease, as well as experiencing relief after recovery, was also motivating for parents.

DISCUSSION

This study examined the experience of oral iron therapy in young children with IDA, as well as factors that affect motivation to adhere, from an in-depth parental perspective. Understanding this information may contribute to the development of effective approaches to facilitate adherence and enhance treatment outcomes. Our cohort included young children with moderate to severe IDA from both primarily English-and primarily Spanish-speaking homes who received a range of iron therapies. Interviews with parents revealed challenges with the treatment regimen and child resistance as barriers to adherence. Facilitators of oral iron adherence included the provision of specific information on the treatment regimen, support from health care providers and additional caregivers within the home, desire to minimize their child’s “traumatic” experiences, strong emotional reactions to different aspects of therapy, and motivation to see their child improve.

Previous research has found that non-adherence in children with both acute and chronic medical conditions is a significant problem, with rates estimated at 30 to 50%.(18) Qualitative research has demonstrated that beliefs about the primary condition and/or treatment, challenges with the treatment regimen, and child resistance to medication all impact adherence.(19, 20) A study of 195 children with IDA found that one-third were non-adherent to treatment due to factors such as child refusal/spit-up, gastrointestinal upset, staining of teeth, and parental discretion.(11) In our study, parents’ lack of knowledge regarding IDA and its negative clinical consequences was not a reported barrier to oral iron treatment. Known negative side effects of oral iron therapy, such as poor taste, were confirmed to make its administration difficult for some.(11)

This study is consistent with previous research in which strong emotional reactions to illness management impact adherence.(21, 22) Emphasis on the value of the treatment, the effect of adherence on treatment outcomes, elicitation of patients’ feelings, and help from family members, are all strategies that have been shown to improve adherence to a medication regimen.(22) Parents in our cohort reported both stress and anxiety related to onset of diagnosis and traumatic experiences, sadness with failure of oral iron therapy, as well as happiness and relief upon their child’s improvement. They reported that positive health outcomes in their child, and help from other caregivers in the home (i.e. grandparent, older sibling), were important in facilitating adherence.

Our findings have important potential implications for clinicians who seek to improve adherence in their affected patients. Most significantly, focusing on drivers of motivation, rather than education on IDA, may help facilitate adherence to a greater extent. For young children with nutritional IDA, this specifically means that health care providers should emphasize health benefits of iron therapy for the child and the ability to minimize future emotional burden and stress with successful iron administration. Within the context of the SDT, acknowledging that parents have a choice in therapy decisions (autonomy), that they have the ability to successfully give iron therapy (competence), especially when provided specific instructions and additional support, and highlighting their sense of parent-child connection (relatedness), therapy adherence should improve. Notably, a smaller subset of parents reported having wished to receive intravenous iron earlier in the treatment course. In the future, it may be important to consider such alternative treatment approaches for families based on their individual values and preferences.

This study has several limitations. First, it was conducted in a specialty clinic at a tertiary care center. Patients present with more severe IDA initially and may be less reflective of the general population with milder IDA. However, we believe that by characterizing this high-risk population, we have learned important information about patient/parent characteristics and parental understanding of IDA and motivation, which will apply broadly to other affected patients. Second, no objective measures of adherence were assessed to determine if there were differences in themes amongst families based on adherence levels. Third, the majority of our population identified as Hispanic/Latino. Though Hispanic/Latino children are disproportionately affected by this condition, this is likely also reflective of our center’s urban setting in a city with a high Hispanic/Latino population, and the large number of patients from low socioeconomic status backgrounds it serves.(2) Children from all racial and ethnic groups are affected by IDA, and we performed continuous review of our qualitative data and enrolled parents until no new information or themes emerged to maximize our ability to communicate the parents’ voice. Enrolling Hispanic/Latino parents from both primarily English-speaking and primarily-Spanish speaking homes also allowed us to ensure that future intervention message content adapted for both English and Spanish-speaking families would have formative data to support it. Finally, Spanish-speaking families were not specifically asked about the provision of instructions in Spanish, nor was health literacy formally assessed. These two aspects would be important to address in future related studies.

Parents of children with IDA experience barriers to adherence common to other conditions. Facilitators of oral iron adherence was reflective of both common motivating factors as well as specific and novel considerations for this young patient population. Data from this study will inform the message content for a behavioral intervention aimed to improved adherence to oral iron therapy in parents of young children with nutritional IDA. High risk groups, in particular, such as Hispanic/Latino patients from both primarily English-and Spanish-speaking homes, and those of low socioeconomic status, would stand to benefit most. Adherence interventions should aim to address parental motivation by emphasizing that adherence to oral therapy improves health outcomes and avoids the stress and anxiety related to more prolonged or invasive treatments.

LIST OF ABBREVIATIONS

IDA

iron deficiency anemia

SDT

self-determination theory of motivation