Comparison of spirometry performed in TN practices and UC practices in the first six months

The effect of the order of intervention on recruitment in the second period had been anticipated during the design of the intervention study and an a priori decision had been made to compare outcome data on the models of spirometry in practices using the first period intervention data only.

6.2.1 Recruitment

Total study recruitment in the first six-month period was 956 participants in eight practices. TN practices recruited 805 participants of whom 531 participants in the target group had spirometry and 252 participants declined spirometry. UC practices recruited 151 participants, of whom 87 participants were in the target group (Figure 5.1). Both study arms recruited fewer participants for spirometry than had been anticipated in sample size calculations during the study design. In TN practices it was assumed nurses would each recruit 30 participants per week. The actual

recruitment was 805, an average of 15.5 participants per week, with 10.2 spirometry tests being performed on participants in the target group per week. The poor level of recruiting in practice 8 was responsible for loss of around 25% from the anticipated level. In addition, pre-study estimates had not taken into account differences in practice sizes and population. If all practices had recruited at the level of the highest recruiting practice, the study would have recruited around 70% of the pre-study estimate.

6.2.2 Comparison of number of spirometry tests in the target group in the TN and UC models

In a comparison of the absolute number of spirometry tests carried out on

participants in the target group, TN intervention practices tested over six times more patients than UC practices, performing 531 opportunistic tests compared to 87 tests.

6.2.3. Proportions of the target group undergoing spirometry in TN and UC models

In order to calculate the number of potential participants eligible for spirometry in each arm of the study, estimates of the eligible population comprising the

denominator were made in TN and UC models using the following methods.

6.2.3.1 Proportion of target group undergoing spirometry TN model practices In TN practices, the total eligible population (NTN) consisted of all patients aged 35 or older who had ever smoked and who were attending the practices for any reason during opportunistic spirometry sessions. It was assumed that all potential

participants would have the opportunity to participate, however early experience in some practices indicated that not all patients in the target group received an invitation from the receptionists, thereby invalidating this assumption. Recruitment procedures were changed where necessary to ensure an invitation was offered to every patient in the target group who attended. Trained nurses and receptionists asked all patients in the waiting rooms. Data on patients attending were collected. The number of people booked to attend during opportunistic spirometry sessions (Nb)couldbe divided into the numbers in categories: agreeing to spirometry (ns), refusing (nr),life long non- smokers (nn), under 35 years old (ny) plus the number previously asked (np) and missed an invitation to participate (nm).

Nb= ns + nr + nn + ny +np + nm

Data collected during spirometry sessions were used to calculate the proportions of people in the five categories. The proportion unaccounted for were assumed to have missed an invitation. The mean proportions are shown in Table 6.4. The calculation of potential participants who missed an invitation to participate could not be

performed for practice 8, as data were lacking. As discussed in section 6.1.1, the demographic profile of patients attending practice 8 differed from the other practices. Fewer patients were in the target group and only limited data were obtained on

patients during spirometry sessions, therefore the average proportion from the other practices was used.

The number of patients in the target group who missed an invitation to participate (Nm) during six months was calculated as:

Nm = (Ns + Nr) x % missed/100

The size of the overall target population in each practice was calculated as the sum of patients having spirometry (Ns), patients refusing spirometry (Nr) and patients in the target group who missed an invitation to participate (Nm) during six months:

NTN = Ns + Nr + Nm

The calculations of NTN and the proportion of the eligible total that underwent spirometry (PTN) were performed for each practice and four practices overall (Table 6.5).

Overall 58.7% of the eligible target group underwent spirometry in TN practices. The average practice proportion of the eligible target group that underwent spirometry in the four practices was 64.4% (13.8).

In addition to opportunistic recruitment during sessions, spirometry was advertised in practices using posters and this strategy was responsible for recruiting 13

participants. A doctor or other health professional, requested spirometry for eight participants.

Sensitivity analysis was performed in which participants recruited by advertising and referral were excluded. The number of target group participants who had

opportunistic spirometry (Nsos) in TN practices during six months was:

Nsos = 531-8-13= 510 NTN = 904

On this basis the proportion of the eligible target group that underwent opportunistic spirometry (POSTN) was:

Table 6.4: Percentages of patients attending practices during spirometry sessions in six months by categories: under 35 years old, life-long non-smoker, previously asked, agree to spirometry, refuse spirometry and missed invitation.

(NK=not known)

Proportions of all attending patients:

Practice < 35 years Never smoked Asked before Accept Refuse Missed

1 23.8 22.2 14.3 7.2 10.7 21.8

3 26.5 19.6 29.3 8.9 5.5 10.2

5 21.5 22.6 19.5 15.1 9.4 12.7

8 65.0 NK NK NK NK 18.0

Table 6.5: Number of patients in the target group participating in the study in TN practices in six months and percentage undergoing spirometry.

Practice Participants 1 3 5 8 Total Spirometry test (Ns) 193 179 145 14 531 Refused test (Nr) 104 113 34 1 252 Total Ns + Nr 297 292 179 15 783 Missed invitation (Nm) 65 30 23 2 110

Target group total (NTN) 362 323 202 17 904

6.2.3.2 Proportion of target group undergoing spirometry in UC practices

In UC practices all patients aged 35 or older who had ever smoked were eligible for spirometry if they consulted a GP at least once during the six-month study period (NUC).

This data was not collected during the study in UC practices nor was it feasible to obtain it retrospectively from practices through a search of practice computer records. Reliance on practice records alone would probably have yielded an underestimate as these are known to be substantially incomplete for data such as patients’ smoking status.

Two methods were used to arrive at an estimate of the total number of target group patients who had at least one consultation during the six-month study period. This involved removing from the total number of consultations occurring during this period, those for whom it was a second or subsequent consultation. Two methods of calculating the number of repeat consultations were used and compared. Both methods used data collected on the demographic profile of patients attending the practices during six months when a trained nurse was visiting.

Figure 6.2: Methods used to estimate the eligible number of target group patients with at least one consultation in a practice during six months

Target group patients: