Initial factor solution

Items relating to the HBM a priori constructs were entered into PCA. Five factors with eigenvalues >1.00 were extracted, explaining 33.9%, 13.5%, 11.2%, 8.8% and 8.5% of variance in item scores respectively. Eigenvalues represent the amount of variation that is explained by the factors identified through PCA and it has been recommended that factors with eigenvalues over 1 represent a significant amount of variation (Kaiser 1960). In order to aid interpretation of the factor solution, a Varimax rotation was performed. Varimax rotation was performed to maximise the dispersion of loadings on factors, therefore to maximising high correlations and

93 minimising low correlations between factors (Tabachnick and Fidell 2007). Varimax rotation loads a smaller number of variables (with a higher loading) on each factor resulting in more interpretable clusters of variables on each factor (Field 2005). As shown in Table 4.2, all a priori items loaded in line with theoretical expectations, apart from the item “Using a self-sample kit is convenient because it can be done at home and means that I would not have to make arrangements (e.g. going to the GP surgery/taking time off work/arranging childcare”. This item was expected to load onto component III with the interpretative label of perceived benefits to HPV sampling, but actually loaded onto component I with the interpretative label of self-efficacy. This item was removed from component I and from the whole analysis on conceptual grounds because it did not significantly load on the benefits scale.

Two a priori items loaded >0.36 on two components (Table 4.2). Loading strength and conceptual issues were considered when deciding which a priori item should be retained on each component.

94 Factors were labelled as follows: Factor I perceived self-efficacy, Factor II perceived barriers, Factor III perceived benefits, Factor IV perceived susceptibility, Factor V perceived severity.

Table 4.2: Initial PCA of extended Health Belief Model constructs relating to HPV self-sampling.

Item Factor I II III IV V

How certain are you that you would be able to place the swab into the tube? .898 How certain are you that you would be able to carry out the self-sampling procedure despite other

commitments?

.892

How certain are you that you would be able to carry out the sampling procedure? .857 How certain are you that you would be able to send off the completed test within the time allowed? .857 Using a self-sampling kit is convenient because it can be done at home and means I would not have to

make arrangements (e.g. going to GP surgery/talking time off work/arranging childcare).

.798

How certain are you that you would do the test well enough? .669 -.407

I wouldn’t trust the results of the self-sampling kit. .840

I would be worried about the self-sampling kit getting lost in the post and not reaching the laboratory. .702 .424

I am worried that I would hurt myself using the self-sample kit. -.354 .586

Using a self-sampling kit would be less embarrassing than having a GP or nurse do a smear test. .816 Using a self-sampling kit would mean that no-one will know that I am having cervical screening. .716 Compared with most women your age, how likely do you think it is that you will come into contact

with HPV?

.829

How serious an infection do you think HPV is? .909

95 4.6.1.2 Final factor solution

The final PCA using Varimax rotation and excluding the item “Using a self-sample kit is convenient because it can be done at home and means that I would not have to make arrangements (e.g. going to the GP surgery/taking time off work/arranging childcare” extracted five factors with eigenvalues >1.00, explaining 34.9%, 14.2%, 9.9%, 9.2% and 8.5% of variance in item scores (Table 4.3). Inspection of the scree plot (Figure 4.1) complemented findings based on Kaiser’s criterion outlining a break following the first two components and then a further break following the fifth component.

Figure 4.1: Scree plot

Nine items strongly loaded on one component independently. Three items loaded on two components each. Statistical and theoretical considerations were

undertaken when deciding which item should be retained on which factor. The item

“I am worried that I would hurt myself using the self-sample kit” will be used to exemplify this process. It was decided that this item would be incorporated into component II because its factor loading was higher on component II than I, and the remaining variables in component II were theoretically related to the item. The same principles were applied to the other items that loaded onto more than one

96 component. Overall, the results of the final rotated PCA supported the five a priori constructs and their related items. Table 4.4 presents the final factor-derived scales and items.

97

Item Factor I II III IV V

How certain are you that you would be able to place the swab into the tube? .890 How certain are you that you would be able to carry out the self-sampling procedure despite other

commitments?

.884

How certain are you that you would be able to carry out the sampling procedure? .877 How certain are you that you would be able to send off the completed test within the time allowed? .836

How certain are you that you would do the test well enough? .703 -.378

I wouldn’t trust the results of the self-sampling kit. .834

I would be worried about the self-sampling kit getting lost in the post and not reaching the laboratory.

.710 .417

I am worried that I would hurt myself using the self-sample kit. -.376 .576

Using a self-sampling kit would be less embarrassing than having a GP or nurse do a smear test. .818 Using a self-sampling kit would mean that no-one will know that I am having cervical screening. .738 Compared with most women your age, how likely do you think it is that you will come into contact

with HPV?

.837

How serious an infection do you think HPV is? .910

Factors were labelled as follows: Factor I perceived self-efficacy, Factor II perceived barriers, Factor III perceived benefits, Factor IV perceived susceptibility, Factor V perceived severity.

Table 4.3: Final rotated PCA of Health Belief Model constructs relating to HPV self-sampling.

98 Component number and

corresponding HBM construct

Item/s loading on component

Component 1

Perceived Self-Efficacy

How certain are you that you would do the test well enough?

How certain are you that you would be able to carry out the sampling procedure (placing swab in vagina)?

How certain are you that you would be able to place the swab into the tube containing the special liquid without touching or dropping the swab?

How certain are you that you would be able to carry out the self-sampling procedure despite other commitments (e.g. work/children)?

How certain are you that you would be able to send off the completed test within the time allowed (2 weeks)?

Component 2

Perceived barriers to HPV self-sampling

I am worried that I would hurt myself using the self-sample kit. Please circle a number.

I wouldn’t trust the results of the self-sample kit.

I would be worried about the self-sampling kit getting lost in the post and not reaching the laboratory.

Component 3 Using a self-sample kit would mean that no-one will know that I am having cervical screening.

99 Table 4.4: Final factor-derived scales and items

Perceived benefits to HPV self-sampling

Using a self-sample kit would be less embarrassing than having a GP or nurse do a smear test.

Component 4

Perceived susceptibility to HPV infection

Compared to most women your age, how likely do you think it is that you will come into contact with HPV?

Component 5

Perceived severity of HPV infection

How serious an infection do you think HPV is?

100 4.6.1.3 Internal consistency of factor-derived scales

Benefits and barriers to HPV self-sampling

Internal consistency of the two perceived benefits items was low (Cronbach’s α=0.555). The inter-item correlation was r=.386, within the accepted range of 0.2 and 0.4 (Briggs and Cheek 1986). Items were combined to form a perceived benefits scale, with a score range of 2 to 10 (a higher score indicating more perceived

benefits of HPV self-sampling).

Perceived barriers items had a Cronbach’s α of 0.582. Inspection of the mean inter-item correlation r=0.315 suggested that the three inter-items exhibited internal

consistency and were aggregated into a perceived barriers to HPV self-sampling scale, with a score range of 3 to 15 (a higher score indicating more perceived barriers).

Perceived benefits and perceived barriers to cervical smear tests

Perceived benefits of cervical smear tests scale initially consisted of three items (Table 4.4, component 3). Items had a moderate Cronbach’s alpha value of 0.690 with an inter-item correlation of r=0.416. Removing the item “Going for cervical smear tests means that cervical abnormalities would be found early on” improved the internal consistency of the scale (α=0.805, r=0.674). Therefore, the scale was formed with two items, with a score range of 2 to 10.

Perceived barriers to cervical smear tests scale consisted of four items (Table 4.4, component 2). Internal consistency of perceived barriers items was low (α=0.448, r=.173). The scale was comprised of four items with a score range of 4 to 20.

101 Self-efficacy in relation to HPV self-sampling

Perceived self-efficacy consisted of five items (Table 4.4) with high internal consistency (α=0.900, r=.664). Inter-item correlation indicated that Cronbach’s α would be slightly higher if item “How certain are you that you would do the test well enough?” was removed (0.917). Exploratory cross-tabulation indicated that

responses to this item exhibited variation when compared to the other self-efficacy item responses. However, self-efficacy in relation to HPV self-sampling is a

combination of both a general belief that one would be able to carry out self-sampling (as measured by this item) as well as the succession of tasks associated with actually carrying out the self-sampling procedure (the other self-efficacy items). It was therefore decided to retain item “How certain are you that you would do the test well enough?” in the self-efficacy scale to reflect the complex nature of perceived self-efficacy. The self-efficacy scale therefore consisted of 5 items with a score range of 5 to 25 (a higher score indicating higher self-efficacy).

The self-efficacy scale was recoded into a binary scale to help differentiate between individuals who perceived higher versus lower self-efficacy in their ability to

conduct HPV self-sampling. Group one reflected lower self-efficacy (respondents who scored lower 1, 2, or 3 on any of the self-efficacy items), whilst group two reflected higher self-efficacy (individuals who scored consistently 4 or 5 on every self-efficacy item). As shown in Table 4.5, the recoded variables were then grouped to make up the self-efficacy scale (ranging from 5 to 10). Women who scored 10 (therefore were in group two for each question) were defined as having a higher self-efficacy, whilst women scoring between 5-9 were defined has having a lower self-efficacy.

102

Recoded self-efficacy scale value

Frequency Valid

%

Cumulative % Higher/Lower self-efficacy

5 17 8.9 8.9 Lower self-efficacy

Table 4.5: Development of binary self-efficacy scale.

Intention to HPV self-sample

Intention to HPV self-sample was measured using four items (Table 4.1, component 1).

Internal consistency of the four intentions items was high (Cronbach’s α=0.916) with a mean inter-item correlation of r=0.749. Excluding the item “How likely would you be to use the self-sampling kit instead of going for a smear test?” would

increase the Cronbach’s alpha value to α=.939, as well as the mean item correlation r=0.841. Exploratory cross-tabulations identified that responses to this item were not consistent compared with response to the other intention items. Therefore, it was decided to exclude this item. The intention scale was computed from three items, scored from 3 to 15 (a higher score indicating higher intention).

The intention scale was negatively skewed, with the majority of respondents being in favour of HPV self-sampling. A binary intention variable was created: those who had a higher intention to HPV self-sample scored 4 or 5 on all three intention items, and those who were less likely to HPV self-sample scored 3 or under on any

intention item. As shown in Table 4.6, a score of 1, 2 or 3 on the 5 point scale was recoded as 1, whilst a score of 4 or 5 was recoded as 2. The recoded variables were then computed to develop a scale (from 3 to 6). Women who scored 6 consistently answered 4 or 5 on all three intention items, whilst women scoring 3-5 scored either inconsistently between the three items or scored lower on all items.

103

Recoded Intention Scale Value

Frequency Valid % Cumulative % Higher/Lower Intention

3 25 13 13 Lower Intention

4 17 8.9 21.9

5 17 8.9 30.7

6 133 69.3 100 Higher Intention

Table 4.6: Development of binary intention variable.

In document Women’s intentions to Human Papillomavirus self-sample: development of an intervention to increase self-sampling intentions (Page 110-121)