# Abstract

 

## Objective Internet-delivered interventions can effectively change health risk behaviors and their determinants, but adherence to intervention websites once they are accessed is very low. This study tests whether and how social presence elements can increase website use. 

## Methods A website about Hepatitis A, B, and C virus infections was used in a preparatory lab-based eye-tracking study assessing whether social presence elements attract participants' attention, because this is a prerequisite for affecting website use. In the following field study, 482 participants representative of the Dutch population were randomized to either a website with or a website without social presence elements. Participants completed a questionnaire of validated measures regarding user perceptions immediately after exposure to the website. Server registrations were used to assess website use. 

## Results Participants in the experimental condition focused on the social presence elements, both in terms of frequency (*F*(1, 98) = 40.34, *p*\<.001) and duration (*F*(1, 88) = 39.99, *p*\<.001), but did not differ in website use in comparison with the control condition; neither in terms of the number of pages visited (*t*(456) = 1.44, *p* = .15), nor in terms of time on the website (*t*(456) = 0.01, *p* = .99). 

## Conclusions Adding social presence elements did not affect actual use of an intervention website within a public health context. Possible reasons are limited attention for these elements in comparison with the main text and the utilitarian value of intervention websites. # Results 

## Participants Of those 982 potential participants that were invited, 458 participated in the study (47%). Half of the participants were female and the mean age of participants was 49 years (*SD* = 16). Of the participants, 30% had a low level of highest completed education (equivalent to primary school/junior high school), 38% an intermediate level (equivalent to senior high school/junior college), and 32% a high level (equivalent to college/university). Those 458 that participated were invited to complete the follow-up measure and 402 of them did so (88%). There was no selective dropout regarding gender (χ2 (1, N = 458) = 0.3, *p* = .57), level of education (χ2 = 5.0, *p* = .08), or Hepatitis knowledge at baseline (*t*(456) = 1.83, *p* = .07). Furthermore, dropout did not differ between the two conditions (χ2 (1, N = 458) = 3.2, *p* = .08). Those who dropped out, however, were younger (*M* = 43 vs 50 years, (*t*(456) = 3.19, *p* = .002). 

## Manipulation check Participants in the experimental condition scored higher on perceived social presence than the control condition (*M* = 4.9 vs. 4.4, *t*(456) = 4.11, *p*\<.001, Cohen's d = 0.38), which indicates that the manipulation did succeed. This effect can be classified as small. 

## Website use and Hepatitis knowledge Participants in the experimental condition did not differ in website use in comparison with the control condition; neither in terms of the number of pages visited, nor in terms of time on the website ([Table 1](#)). Effect sizes were trivial. Thus, there is no support for Hypothesis 1. The increase in Hepatitis knowledge between pre-test and post-test did not differ between both conditions (*F*(1, 400) = 0.72, *p* = .40), but there was a significant increase regarding Hepatitis knowledge between pre-test and post-test across conditions (*M* = 6.4 vs. 8.3, *F*(1,400) = 172.98, *p*\<.001, Cohen's d = 0.65), which can be defined as a moderate effect size. ::::table-wrap

10.1371/journal.pone.0057067.t001

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## Differences in website use between conditions.

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Variable Experimental condition Control condition *t* *p* Cohen's d

______________________________________________________________________

```
                        M                        SD                  M       SD                         
```

Number of pages (0--12) 7.5 4.0 8.0 3.8 1.44 .15 0.14
Time on website (sec) 151.0 117.4 150.8 107.8 0.01 .99 0.00:::: 

## User perceptions There were no differences between conditions in terms of efficiency (*F*(1, 456) = 0.84, *p* = .36), effectiveness (*F*(1, 456) = 0.03, *p* = .87), enjoyment (*F*(1, 456) = 0.08, *p* = .78), active trust (*F*(1, 456) = 0.03, *p* = .87) and interest (*F*(1, 456) = 0.07, *p* = .80). [Figure 5](#) illustrates the final structural equation model testing the associations between user perceptions and website use across conditions, because there were no differences on both measures of website use. The final model is mostly in line with Hypothesis 2: Efficiency (*M* = 6.5, *SD* = 0.84), effectiveness (*M* = 6.4, *SD* = 0.87), and enjoyment (*M* = 5.6, *SD* = 1.21) were positively associated with website use and these associations were partly mediated by active trust (*M* = 5.8, *SD* = 1.23). The association between efficiency and website use, however, was fully mediated by active trust. Since there were no differences between conditions in terms of website use, there is neither support for Hypothesis 3a nor for Hypothesis 3b. Interest (*M* = 5.9, *SD* = 1.06), however, was positively associated with and contributed to explaining variance in website use besides efficiency, effectiveness, enjoyment, and active trust. The explained variance (R^2^) of the number of pages visited and time on the website is .63 and .51 respectively. The CFI and TLI are .98 and .97, respectively; RMSEA and SRMR are .06 and .04, respectively. All of these fit indices indicate a close fit for the final model. <figure> 10.1371/journal.pone.0057067.g005 <p><img src="" /></p> <figcaption>Final model including standardized betas of significant paths within the model.</figcaption> </figure>


Extracted trial result:
Outcome: website use in terms of the number of pages visited (continuous)
Intervention: website with social presence elements.
Comparator: website without social presence elements.
Intervention mean: 7.5
Intervention standard deviation: 4
Comparator mean: 8
Comparator standard deviation: 3.8
Notes: Cannot find the group sizes in the text or table.