. through 
 participation in social networking services , important relationships can be formed1 . as smartphone functions become more varied 
 and complex studies on the 
 functionality and usability of smartphones1,2,3 and 
 their effects on the body4 , 5 have been conducted to address these trends . three scenarios that require users to operate smartphones with 
 one - hand have been identified by jeon7 ; 
 namely , when they are carrying baggage in one hand , when they are walking , and when they 
 can not use two hands owing to a physical disability . most stroke patients are afflicted with hemiparalysis ; as a result , regardless of whether 
 it is pre - dominant hand or not , these patients must only use one hand . the functionality and 
 usability of smartphones will be different for stroke patients than for non - disabled people . 
 in some cases , stroke patients must change their dominant hand because the side of their 
 pre - dominant hand is paralyzed . the aim of this study was to investigate differences in 
 functionality and usability among three smartphone screen sizes for stroke patients who are 
 limited to the use of one hand , and to investigate the differences in terms of smartphone 
 usage between the pre - dominant hand and non - dominant hand . the patients included in this study were those who ( 1 ) had hemiplegia following a stroke , 
 ( 2 ) were able to understand the task and express themselves , ( 3 ) had some experience in 
 using a cell phone , and ( 4 ) provided consent to participate in the study . patients excluded from the study included those suffering from tremors , involuntary 
 movements , cognitive impairment , or visual problems . five participants suffered from right hemiplegia and eight suffered from left hemiplegia ; 
 thus , there were eight pre - dominant hand users and five pre - non - dominant hand users ( table 1table 1.general characteristics of participantsgroup for pre - non - dominant hand(n=5 ) group for pre - dominant hand(n=8)gendermale46female12age40s2450s34affected sideright50left08pre - dominant handright58left00duration of smartphone use after onsetless than 3 years10more than 3 , less than 511more than 537thumb space ( cm)11.900.8212.400.49*p<0.05 ) . three smartphone screen sizes4.2 , 4.5 , and 5.6 inch screens  were used in this study . in a 
 previous study8 , the smartphones in this study are 
 listed in table 2table 2.characteristics of the used phonestype of the mobilesize of the mobile size of the displayg * * mobile phone by company151.2 * 79.5 * 8.35.6*p<0.05 . for usability testing , the prototype containing the screen sections was 
 printed on transparencies fitted to the sizes of the smartphone screen , which were 
 subsequently attached to the smartphones . participants performed dragging operations along 
 the sections , using the simplest operation among the six common input interactions8 . the participants assessed discomfort while 
 performing two - way drags in the sections between numbers 13 , 57 , 911 , 19 , 210 , 311 , 
 111 and 39 . data coding for left - hand users was converted to be symmetric with that of 
 right - hand users . the discomfort was measured using a four - point likert scale : one point 
 indicated that the operation was extremely comfortable , two points indicated that it was 
 easy , three points indicated discomfort , and four points indicated extreme discomfort ( fig . 1fig . for functionality , the participants quickly touched the numbers 0 through 9 in order on the 
 keypad , and the assessor measured the completion time and number of errors . data analysis was conducted using spss 20.0 statistical software . to test homogeneity 
 between two groups ,  and mann - whitney tests were conducted . to compare 
 functionality and usability among the three sizes of smartphone screens , if significant differences were noted among the three sizes , a 
 mann - whitney test was conducted to separately compare the two sizes . the significant values 
 in the kruskal - wallis and mann - whitney tests were set to 0.05 and 0.016 , respectively . to 
 compare the functionality and usability between dominant hand and non - dominant hand 
 operations , no significant differences were noted in the general characteristics of non - dominant and 
 dominant hand users ( table 1 ) . usability 
 differences among the three screen sizes were not found for non - dominant hand users ; 
 however , in dominant hand users , differences were found ( p<0.016 ) among the three screen 
 sizes for sections 311 , 111 , and 210 . usability differences between dominant and 
 non - dominant hand users were found in three sections of the 5.6 inch screen , four sections 
 of the 4.5 inch screen , and six sections on the 4.2 inch screen ( p<0.05 ) ( table 3table 3.the usability according to the size of smartphone and comparison between dominant 
 and non - dominant hand user group4.2 inch4.5 inch5.6 inch13total1.380.511.380.511.920.95non - dominant1.800.451.600.552.600.89dominant1.130.351.250.461.500.7657total1.380.511.540.522.001.22non - dominant1.500.452.000.003.001.22dominant1.130.351.250.461.370.74911total1.380.511.540.522.001.22non - dominant1.800.452.000.003.401.34dominant2.371.061.370.522.000.75210total1.850.902.151.213.770.44non - dominant2.800.453.200.843.800.45dominant1.250.461.500.933.750.4619total2.921.123.381.123.850.38non - dominant3.800.453.800.454.000.00dominant2.371.063.121.363.750.46311total2.381.262.231.093.460.52non - dominant3.600.893.200.843.800.45dominant1.630.741.630.743.250.46111total2.540.972.310.953.690.48non - dominant3.400.552.801.094.000.00dominant2.000.752.000.753.500.5339total3.080.863.001.003.850.38non - dominant3.600.893.600.894.000.00dominant2.750.712.630.923.750.46 significant difference at 0.016 between 4.2 and 4.5 inch . * significant difference at 0.05 between dominant hand use group and non - dominant hand 
 use group ) . * significant difference at 0.05 between dominant hand use group and non - dominant hand 
 use group no differences in completion time were found among the three screen sizes in the 
 non - dominant hand users ; however , for dominant hand users , completion time differences were 
 found between the operations performed on the 4.2 and 5.6inch screens and between the 
 operations performed on the 4.5 and 5.6 inch screens ( p<0.016 ) . among the three screen 
 sizes , no differences in frequency errors were found in both dominant and non - dominant hand 
 users ( p>0.016 ) . completion time differences between non - dominant and dominant hand users 
 were found for all screen sizes ( p<0.05 ) . significant differences in frequency of errors 
 between non - dominant and dominant hand users were found when 4.2 and 4.5 inch screens were 
 used ( p<0.05 ) , but not when 5.6 inch screens were used ( p>0.05 ) ( table 4table 4.the functionality according to the size of smartphone4.2 inch4.5 inch5.6 inchtime ( sec.)total8.373.987.453.0410.064.87non - dominant11.273.2210.602.7214.165.30dominant7.502.245.500.485.310.42number of errorstotal1.151.190.761.091.231.16non - dominant2.802.951.601.342.403.29dominant0.130.350.250.460.500.53 significant difference at 0.016 between 4.2 and 4.5 inch . * significant difference at 0.05 between dominant hand use group and non - dominant hand 
 use group ) . * significant difference at 0.05 between dominant hand use group and non - dominant hand 
 use group when using a smartphone , users typically prefer using one - hand instead of both hands . the 
 size of the smartphone is a key factor in determining whether users operate their 
 smartphones with one hand or both hands9 . 
 because of hemiparalysis this study investigated smartphone usability and functionality for stroke 
 patients and considered three sizes of smartphone screens and whether the patients used 
 their pre - dominant hand or not . analysis on usability among the three smartphones screen sizes for dominant hand users 
 showed that stroke patients experienced significantly more discomfort in only three 
 sections : 311 , 111 , and 210 . im8 reported that users operating their 
 smartphones with one hand were satisfied with all input modes when using a 3.5 inch screen , 
 some input modes when using a 4.0 , 4.5 , or 5.0 inch screen , but dissatisfied with most input 
 modes when using a 5.5 inch screen . however , the result of this study indicated that the 
 smaller the smartphone screen , the larger the difference in usability between the dominant 
 and non - dominant hand . it should be interpreted that the smaller the smartphone size , the 
 more it required thumb sensitivity . regardless of the size of the smartphone , the completion time and usability between 
 dominant and non - dominant hands were significantly different . it was considered that the 
 pre - non - dominant hand user was not skillful at using a smartphone than the pre - dominant hand 
 user . both hands must be assessed because the performance of the dominant and non - dominant 
 hands is different , as reported by perry and hourcade10 . to the best of our knowledge , this is the first study to analyze 
 smartphone functionality and usability for stroke patients while considering both the 
 pre - dominant and pre - non - dominant hand . when 4.2 and 4.5 inch screens were used , a significant difference in the frequency of 
 errors was found between non - dominant and dominant hand users , but not when 5.6 inch screens 
 were used . it assessed functionality and usability while the 
 smartphone was being held in the vertical position ; horizontal position was not considered . many variables such as flexibility of the thumb , smartphone grip patterns , and smartphone 
 weight6 , were not considered in this 
 study . in the future , studies on smartphone functionality and usability of patients with 
 stroke using only pre - non dominant hand need to be conducted .
[ purpose ] the effect of screen size on smartphone functionality and usability for 
 patients with stroke , considering both the non - dominant and dominant hand smartphone 
 usage , was investigated in this study . 
 [ subjects and methods ] thirteen patients with 
 stroke participated in this study  five pre - non - dominant hand users and eight pre - dominant 
 hand users . 
 the smartphone screen sizes used were 4.2 , 4.5 , and 5.6 inches . 
 usability was 
 assessed in terms of discomfort experienced during dragging operations , which was 
 self - reported using a four - point likert scale . 
 functionality was assessed in terms of 
 completion time and the frequency of errors in the task requiring users to quickly touch 
 numbers 0 through 9 in order on the keypad . 
 [ results ] for all three screen sizes , a 
 significant difference between the dominant and non - dominant hands was found in usability , 
 completion time , and frequency of errors . for dominant hand users , differences in 
 usability and completion time 
 were found among the three screen sizes . among the three 
 screen sizes , 
 no difference in the frequency of errors was found in either of the groups . 
 [ conclusion ] this study will be useful as basic research on usability and functionality 
 with stroke patients using only pre - non - dominant or pre - dominant hand .